diff --git a/pnpm-lock.yaml b/pnpm-lock.yaml
index c046a2c..fb61688 100644
--- a/pnpm-lock.yaml
+++ b/pnpm-lock.yaml
@@ -67,6 +67,9 @@ importers:
       solid-js:
         specifier: ^1.9.5
         version: 1.9.13
+      stripe:
+        specifier: ^22.1.1
+        version: 22.1.1(@types/node@25.9.1)
       tailwindcss:
         specifier: ^4.0.0
         version: 4.3.0
@@ -3130,6 +3133,15 @@ packages:
   strip-literal@3.1.0:
     resolution: {integrity: sha512-8r3mkIM/2+PpjHoOtiAW8Rg3jJLHaV7xPwG+YRGrv6FP0wwk/toTpATxWYOW0BKdWwl82VT2tFYi5DlROa0Mxg==}
 
+  stripe@22.1.1:
+    resolution: {integrity: sha512-cmodIYP27tBkJ8G7DuGgWw0PFuemlFZbuF3Wwr1TrjFjUa3T7NIgCe6TVwX8BO2ynu+xtTuDGfHafNDCPt9lXA==}
+    engines: {node: '>=18'}
+    peerDependencies:
+      '@types/node': '>=18'
+    peerDependenciesMeta:
+      '@types/node':
+        optional: true
+
   supports-color@10.2.2:
     resolution: {integrity: sha512-SS+jx45GF1QjgEXQx4NJZV9ImqmO2NPz5FNsIHrsDjh2YsHnawpan7SNQ1o8NuhrbHZy9AZhIoCUiCeaW/C80g==}
     engines: {node: '>=18'}
@@ -6431,6 +6443,10 @@ snapshots:
     dependencies:
       js-tokens: 9.0.1
 
+  stripe@22.1.1(@types/node@25.9.1):
+    optionalDependencies:
+      '@types/node': 25.9.1
+
   supports-color@10.2.2: {}
 
   supports-color@7.2.0:
diff --git a/web/.env.example b/web/.env.example
index 1baeffc..e3e51e8 100644
--- a/web/.env.example
+++ b/web/.env.example
@@ -1 +1,8 @@
 DATABASE_URL="postgresql://postgres:postgres@localhost:5432/shieldai"
+
+# Stripe (get test keys from https://dashboard.stripe.com/test/apikeys)
+STRIPE_SECRET_KEY="sk_test_..."
+STRIPE_WEBHOOK_SECRET="whsec_..."
+STRIPE_PRICE_BASIC="price_basic"
+STRIPE_PRICE_PLUS="price_plus"
+STRIPE_PRICE_PREMIUM="price_premium"
diff --git a/web/package.json b/web/package.json
index c51806a..f63a5fe 100644
--- a/web/package.json
+++ b/web/package.json
@@ -28,6 +28,7 @@
     "jose": "^5",
     "pg": "^8.21.0",
     "solid-js": "^1.9.5",
+    "stripe": "^22.1.1",
     "tailwindcss": "^4.0.0",
     "three": "^0.184.0",
     "valibot": "^0.29.0",
diff --git a/web/src/routes/api/stripe/webhook.ts b/web/src/routes/api/stripe/webhook.ts
new file mode 100644
index 0000000..9773a65
--- /dev/null
+++ b/web/src/routes/api/stripe/webhook.ts
@@ -0,0 +1,27 @@
+import type { APIEvent } from "@solidjs/start/server";
+import { stripe } from "~/server/stripe";
+import { handleWebhookEvent } from "~/server/services/billing.service";
+
+export async function POST(event: APIEvent) {
+  const body = await event.request.text();
+  const signature = event.request.headers.get("stripe-signature");
+
+  if (!signature) {
+    return new Response("Missing stripe-signature header", { status: 400 });
+  }
+
+  try {
+    const webhookEvent = stripe.webhooks.constructEvent(
+      body,
+      signature,
+      process.env.STRIPE_WEBHOOK_SECRET ?? "",
+    );
+
+    await handleWebhookEvent(webhookEvent);
+
+    return new Response("OK", { status: 200 });
+  } catch (err) {
+    const message = err instanceof Error ? err.message : "Webhook error";
+    return new Response(message, { status: 400 });
+  }
+}
diff --git a/web/src/server/api/root.ts b/web/src/server/api/root.ts
index adeb0f5..980f2b9 100644
--- a/web/src/server/api/root.ts
+++ b/web/src/server/api/root.ts
@@ -1,10 +1,12 @@
 import { exampleRouter } from "./routers/example";
 import { userRouter } from "./routers/user";
+import { billingRouter } from "./routers/billing";
 import { createTRPCRouter } from "./utils";
 
 export const appRouter = createTRPCRouter({
   example: exampleRouter,
   user: userRouter,
+  billing: billingRouter,
 });
 
 export type AppRouter = typeof appRouter;
diff --git a/web/src/server/api/routers/billing.test.ts b/web/src/server/api/routers/billing.test.ts
new file mode 100644
index 0000000..4a5319e
--- /dev/null
+++ b/web/src/server/api/routers/billing.test.ts
@@ -0,0 +1,241 @@
+import { describe, it, expect, vi, beforeEach } from "vitest";
+import { initTRPC, TRPCError } from "@trpc/server";
+import { wrap } from "@typeschema/valibot";
+import {
+  CreateCheckoutSessionSchema,
+  CreatePortalSessionSchema,
+  CancelSubscriptionSchema,
+  ReactivateSubscriptionSchema,
+  ListInvoicesSchema,
+} from "../schemas/billing";
+
+vi.mock("~/server/services/billing.service", () => ({
+  getOrCreateCustomer: vi.fn(),
+  createCheckoutSession: vi.fn(),
+  createPortalSession: vi.fn(),
+  cancelSubscription: vi.fn(),
+  reactivateSubscription: vi.fn(),
+  listInvoices: vi.fn(),
+}));
+
+const { mockFindFirst } = vi.hoisted(() => ({
+  mockFindFirst: vi.fn(),
+}));
+
+vi.mock("~/server/db", () => ({
+  db: {
+    query: {
+      subscriptions: {
+        findFirst: mockFindFirst,
+      },
+    },
+  },
+}));
+
+import {
+  createCheckoutSession,
+  createPortalSession,
+  cancelSubscription,
+  reactivateSubscription,
+  listInvoices,
+} from "~/server/services/billing.service";
+import { db } from "~/server/db";
+
+const mockCreateCheckoutSession = vi.mocked(createCheckoutSession);
+const mockCreatePortalSession = vi.mocked(createPortalSession);
+const mockCancelSubscription = vi.mocked(cancelSubscription);
+const mockReactivateSubscription = vi.mocked(reactivateSubscription);
+const mockListInvoices = vi.mocked(listInvoices);
+const mockDb = vi.mocked(db);
+
+type User = {
+  id: string; email: string; name: string | null; image: string | null;
+  role: "user" | "family_admin" | "family_member" | "support"; emailVerified: Date | null; deletedAt: Date | null;
+  stripeCustomerId: string | null;
+  createdAt: Date; updatedAt: Date;
+};
+
+type Ctx = { db: object; user: User | null; apiKey: string | null };
+
+const baseUser: User = {
+  id: "user-1", email: "a@b.com", name: "Test", image: null,
+  role: "user", emailVerified: null, deletedAt: null,
+  stripeCustomerId: "cus_123",
+  createdAt: new Date(), updatedAt: new Date(),
+};
+
+function makeUser(overrides: Partial<User> = {}): User {
+  return { ...baseUser, ...overrides };
+}
+
+function createCaller(user: User | null) {
+  const t = initTRPC.context<Ctx>().create();
+  const isAuthed = t.middleware(({ ctx, next }) => {
+    if (!ctx.user) throw new TRPCError({ code: "UNAUTHORIZED" });
+    return next({ ctx: { ...ctx, user: ctx.user } });
+  });
+
+  const router = t.router({
+    getSubscription: t.procedure.use(isAuthed)
+      .query(async () => {
+        const sub = await mockFindFirst();
+        return sub ?? null;
+      }),
+    createCheckoutSession: t.procedure.use(isAuthed)
+      .input(wrap(CreateCheckoutSessionSchema))
+      .mutation(async ({ ctx, input }) => {
+        const i = input as { priceId: string; successUrl: string; cancelUrl: string };
+        return mockCreateCheckoutSession(ctx.user.id, ctx.user.email, i.priceId, i.successUrl, i.cancelUrl);
+      }),
+    createPortalSession: t.procedure.use(isAuthed)
+      .input(wrap(CreatePortalSessionSchema))
+      .mutation(async ({ ctx, input }) => {
+        const i = input as { returnUrl: string };
+        if (!ctx.user.stripeCustomerId) {
+          throw new TRPCError({ code: "NOT_FOUND", message: "No Stripe customer found" });
+        }
+        return mockCreatePortalSession(ctx.user.stripeCustomerId, i.returnUrl);
+      }),
+    cancelSubscription: t.procedure.use(isAuthed)
+      .input(wrap(CancelSubscriptionSchema))
+      .mutation(async ({ input }) => {
+        const i = input as { subscriptionId: string };
+        return mockCancelSubscription(i.subscriptionId);
+      }),
+    reactivateSubscription: t.procedure.use(isAuthed)
+      .input(wrap(ReactivateSubscriptionSchema))
+      .mutation(async ({ input }) => {
+        const i = input as { subscriptionId: string };
+        return mockReactivateSubscription(i.subscriptionId);
+      }),
+    listInvoices: t.procedure.use(isAuthed)
+      .input(wrap(ListInvoicesSchema))
+      .query(async ({ ctx, input }) => {
+        if (!ctx.user.stripeCustomerId) {
+          return { invoices: [], hasMore: false };
+        }
+        const i = input as { limit?: string; startingAfter?: string };
+        return mockListInvoices(ctx.user.stripeCustomerId, parseInt(i.limit ?? "10", 10), i.startingAfter);
+      }),
+  });
+
+  const caller = t.createCallerFactory(router);
+  return caller({ db: {} as never, user, apiKey: null });
+}
+
+beforeEach(() => {
+  vi.clearAllMocks();
+});
+
+describe("billing.getSubscription", () => {
+  it("returns subscription for authenticated user", async () => {
+    const now = new Date();
+    (mockDb.query.subscriptions.findFirst as ReturnType<typeof vi.fn>).mockResolvedValue({
+      id: "sub-1", userId: "user-1", stripeId: "sub_stripe_1",
+      tier: "premium", status: "active",
+      currentPeriodStart: now, currentPeriodEnd: now,
+      cancelAtPeriodEnd: false,
+      createdAt: now, updatedAt: now,
+    });
+
+    const api = createCaller(makeUser());
+    const result = await api.getSubscription();
+    expect(result).not.toBeNull();
+    expect(result!.tier).toBe("premium");
+    expect(result!.status).toBe("active");
+  });
+
+  it("returns null when user has no subscription", async () => {
+    (mockDb.query.subscriptions.findFirst as ReturnType<typeof vi.fn>).mockResolvedValue(undefined);
+    const api = createCaller(makeUser());
+    const result = await api.getSubscription();
+    expect(result).toBeNull();
+  });
+
+  it("rejects unauthenticated users", async () => {
+    const api = createCaller(null);
+    await expect(api.getSubscription()).rejects.toThrow(TRPCError);
+  });
+});
+
+describe("billing.createCheckoutSession", () => {
+  it("creates checkout session and returns URL", async () => {
+    mockCreateCheckoutSession.mockResolvedValue({
+      url: "https://checkout.stripe.com/session_123",
+      sessionId: "session_123",
+    });
+
+    const api = createCaller(makeUser());
+    const result = await api.createCheckoutSession({
+      priceId: "price_basic",
+      successUrl: "https://example.com/success",
+      cancelUrl: "https://example.com/cancel",
+    });
+
+    expect(result.url).toBe("https://checkout.stripe.com/session_123");
+  });
+});
+
+describe("billing.createPortalSession", () => {
+  it("creates portal session for user with stripeCustomerId", async () => {
+    mockCreatePortalSession.mockResolvedValue({
+      url: "https://billing.stripe.com/portal/session_456",
+    });
+
+    const api = createCaller(makeUser());
+    const result = await api.createPortalSession({
+      returnUrl: "https://example.com/return",
+    });
+
+    expect(result.url).toBe("https://billing.stripe.com/portal/session_456");
+  });
+
+  it("throws NOT_FOUND when user has no stripeCustomerId", async () => {
+    const api = createCaller(makeUser({ stripeCustomerId: null }));
+    await expect(api.createPortalSession({ returnUrl: "https://example.com/return" })).rejects.toThrow(TRPCError);
+  });
+});
+
+describe("billing.cancelSubscription", () => {
+  it("cancels subscription", async () => {
+    mockCancelSubscription.mockResolvedValue({ cancelAtPeriodEnd: true });
+
+    const api = createCaller(makeUser());
+    const result = await api.cancelSubscription({ subscriptionId: "sub_123" });
+
+    expect(result.cancelAtPeriodEnd).toBe(true);
+  });
+});
+
+describe("billing.reactivateSubscription", () => {
+  it("reactivates subscription", async () => {
+    mockReactivateSubscription.mockResolvedValue({ cancelAtPeriodEnd: false });
+
+    const api = createCaller(makeUser());
+    const result = await api.reactivateSubscription({ subscriptionId: "sub_123" });
+
+    expect(result.cancelAtPeriodEnd).toBe(false);
+  });
+});
+
+describe("billing.listInvoices", () => {
+  it("lists invoices for user with stripeCustomerId", async () => {
+    mockListInvoices.mockResolvedValue({
+      invoices: [{ id: "in_1" }, { id: "in_2" }] as never,
+      hasMore: false,
+    });
+
+    const api = createCaller(makeUser());
+    const result = await api.listInvoices({});
+
+    expect(result.invoices).toHaveLength(2);
+  });
+
+  it("returns empty list when user has no stripeCustomerId", async () => {
+    const api = createCaller(makeUser({ stripeCustomerId: null }));
+    const result = await api.listInvoices({});
+
+    expect(result.invoices).toHaveLength(0);
+    expect(result.hasMore).toBe(false);
+  });
+});
diff --git a/web/src/server/api/routers/billing.ts b/web/src/server/api/routers/billing.ts
new file mode 100644
index 0000000..75e76b5
--- /dev/null
+++ b/web/src/server/api/routers/billing.ts
@@ -0,0 +1,100 @@
+import { TRPCError } from "@trpc/server";
+import { eq } from "drizzle-orm";
+import { wrap } from "@typeschema/valibot";
+import { createTRPCRouter, protectedProcedure } from "../utils";
+import {
+  CreateCheckoutSessionSchema,
+  CreatePortalSessionSchema,
+  CancelSubscriptionSchema,
+  ReactivateSubscriptionSchema,
+  ListInvoicesSchema,
+} from "../schemas/billing";
+import {
+  getOrCreateCustomer,
+  createCheckoutSession,
+  createPortalSession,
+  cancelSubscription,
+  reactivateSubscription,
+  listInvoices,
+} from "~/server/services/billing.service";
+import { db } from "~/server/db";
+import { subscriptions } from "~/server/db/schema/subscription";
+
+export const billingRouter = createTRPCRouter({
+  getSubscription: protectedProcedure.query(async ({ ctx }) => {
+    const sub = await db.query.subscriptions.findFirst({
+      where: eq(subscriptions.userId, ctx.user.id),
+    });
+    return sub ?? null;
+  }),
+
+  createCheckoutSession: protectedProcedure
+    .input(wrap(CreateCheckoutSessionSchema))
+    .mutation(async ({ ctx, input }) => {
+      const allowedPrices = [
+        process.env.STRIPE_PRICE_BASIC,
+        process.env.STRIPE_PRICE_PLUS,
+        process.env.STRIPE_PRICE_PREMIUM,
+      ].filter(Boolean);
+
+      if (!allowedPrices.includes(input.priceId)) {
+        throw new TRPCError({
+          code: "BAD_REQUEST",
+          message: "Invalid price ID",
+        });
+      }
+
+      return createCheckoutSession(
+        ctx.user.id,
+        ctx.user.email,
+        input.priceId,
+        input.successUrl,
+        input.cancelUrl,
+      );
+    }),
+
+  createPortalSession: protectedProcedure
+    .input(wrap(CreatePortalSessionSchema))
+    .mutation(async ({ ctx, input }) => {
+      const user = ctx.user;
+      const stripeCustomerId = user.stripeCustomerId;
+
+      if (!stripeCustomerId) {
+        throw new TRPCError({
+          code: "NOT_FOUND",
+          message: "No Stripe customer found",
+        });
+      }
+
+      return createPortalSession(stripeCustomerId, input.returnUrl);
+    }),
+
+  cancelSubscription: protectedProcedure
+    .input(wrap(CancelSubscriptionSchema))
+    .mutation(async ({ input }) => {
+      return cancelSubscription(input.subscriptionId);
+    }),
+
+  reactivateSubscription: protectedProcedure
+    .input(wrap(ReactivateSubscriptionSchema))
+    .mutation(async ({ input }) => {
+      return reactivateSubscription(input.subscriptionId);
+    }),
+
+  listInvoices: protectedProcedure
+    .input(wrap(ListInvoicesSchema))
+    .query(async ({ ctx, input }) => {
+      const user = ctx.user;
+      const stripeCustomerId = user.stripeCustomerId;
+
+      if (!stripeCustomerId) {
+        return { invoices: [], hasMore: false };
+      }
+
+      return listInvoices(
+        stripeCustomerId,
+        parseInt(input.limit ?? "10", 10),
+        input.startingAfter,
+      );
+    }),
+});
diff --git a/web/src/server/api/routers/user.test.ts b/web/src/server/api/routers/user.test.ts
index 5b3d229..d38afda 100644
--- a/web/src/server/api/routers/user.test.ts
+++ b/web/src/server/api/routers/user.test.ts
@@ -30,6 +30,7 @@ const mockUpdateMemberRole = vi.mocked(updateMemberRole);
 type User = {
   id: string; email: string; name: string | null; image: string | null;
   role: "user" | "family_admin" | "family_member" | "support"; emailVerified: Date | null; deletedAt: Date | null;
+  stripeCustomerId: string | null;
   createdAt: Date; updatedAt: Date;
 };
 type Ctx = { db: object; user: User | null; apiKey: string | null };
@@ -97,6 +98,7 @@ function createCaller(user: User | null) {
 const baseUser: User = {
   id: "user-1", email: "a@b.com", name: "Test", image: null,
   role: "user", emailVerified: null, deletedAt: null,
+  stripeCustomerId: null,
   createdAt: new Date(), updatedAt: new Date(),
 };
 
diff --git a/web/src/server/api/schemas/billing.ts b/web/src/server/api/schemas/billing.ts
new file mode 100644
index 0000000..ed1bf19
--- /dev/null
+++ b/web/src/server/api/schemas/billing.ts
@@ -0,0 +1,24 @@
+import { object, string, url, minLength, optional, picklist } from "valibot";
+
+export const CreateCheckoutSessionSchema = object({
+  priceId: string([minLength(1)]),
+  successUrl: string([url()]),
+  cancelUrl: string([url()]),
+});
+
+export const CreatePortalSessionSchema = object({
+  returnUrl: string([url()]),
+});
+
+export const CancelSubscriptionSchema = object({
+  subscriptionId: string([minLength(1)]),
+});
+
+export const ReactivateSubscriptionSchema = object({
+  subscriptionId: string([minLength(1)]),
+});
+
+export const ListInvoicesSchema = object({
+  limit: optional(string(), "10"),
+  startingAfter: optional(string()),
+});
diff --git a/web/src/server/db/schema.test.ts b/web/src/server/db/schema.test.ts
index 2f438a7..0c7b17b 100644
--- a/web/src/server/db/schema.test.ts
+++ b/web/src/server/db/schema.test.ts
@@ -76,17 +76,18 @@ describe("users table", () => {
     expect(colNames).toContain("name");
     expect(colNames).toContain("image");
     expect(colNames).toContain("role");
+    expect(colNames).toContain("stripe_customer_id");
     expect(colNames).toContain("deleted_at");
     expect(colNames).toContain("created_at");
     expect(colNames).toContain("updated_at");
   });
 
-  it("has 9 columns", () => {
-    expect(config.columns).toHaveLength(9);
+  it("has 10 columns", () => {
+    expect(config.columns).toHaveLength(10);
   });
 
-  it("has 2 indexes", () => {
-    expect(config.indexes.length).toBe(2);
+  it("has 3 indexes", () => {
+    expect(config.indexes.length).toBe(3);
   });
 });
 
diff --git a/web/src/server/db/schema/auth.ts b/web/src/server/db/schema/auth.ts
index eb104e8..be9d211 100644
--- a/web/src/server/db/schema/auth.ts
+++ b/web/src/server/db/schema/auth.ts
@@ -8,12 +8,14 @@ export const users = pgTable("users", {
   name: text("name"),
   image: text("image"),
   role: userRole("role").default("user").notNull(),
+  stripeCustomerId: text("stripe_customer_id"),
   deletedAt: timestamp("deleted_at", { withTimezone: true, mode: "date" }),
   createdAt: timestamp("created_at", { withTimezone: true, mode: "date" }).defaultNow().notNull(),
   updatedAt: timestamp("updated_at", { withTimezone: true, mode: "date" }).defaultNow().notNull().$onUpdate(() => new Date()),
 }, (table) => ({
   emailIdx: index("users_email_idx").on(table.email),
   roleIdx: index("users_role_idx").on(table.role),
+  stripeCustomerIdIdx: index("users_stripe_customer_id_idx").on(table.stripeCustomerId),
 }));
 
 export const accounts = pgTable("accounts", {
diff --git a/web/src/server/services/billing.service.test.ts b/web/src/server/services/billing.service.test.ts
new file mode 100644
index 0000000..f23967e
--- /dev/null
+++ b/web/src/server/services/billing.service.test.ts
@@ -0,0 +1,338 @@
+import { describe, it, expect, vi, beforeEach } from "vitest";
+
+vi.mock("~/server/stripe", () => ({
+  stripe: {
+    customers: { create: vi.fn() },
+    checkout: { sessions: { create: vi.fn() } },
+    billingPortal: { sessions: { create: vi.fn() } },
+    subscriptions: { update: vi.fn(), retrieve: vi.fn() },
+    invoices: { list: vi.fn() },
+    webhooks: { constructEvent: vi.fn() },
+  },
+}));
+
+vi.mock("~/server/db", () => ({
+  db: {
+    select: vi.fn(),
+    insert: vi.fn(),
+    update: vi.fn(),
+    query: {
+      subscriptions: {
+        findFirst: vi.fn(),
+      },
+    },
+  },
+}));
+
+import { stripe } from "~/server/stripe";
+import { db } from "~/server/db";
+import {
+  getOrCreateCustomer,
+  createCheckoutSession,
+  createPortalSession,
+  cancelSubscription,
+  reactivateSubscription,
+  listInvoices,
+  handleWebhookEvent,
+} from "./billing.service";
+
+beforeEach(() => {
+  vi.clearAllMocks();
+});
+
+describe("getOrCreateCustomer", () => {
+  it("returns existing stripeCustomerId if present", async () => {
+    (db.select as ReturnType<typeof vi.fn>).mockReturnValue({
+      from: vi.fn().mockReturnValue({
+        where: vi.fn().mockReturnValue({
+          limit: vi.fn().mockResolvedValue([
+            { id: "u1", email: "a@b.com", stripeCustomerId: "cus_existing" },
+          ]),
+        }),
+      }),
+    });
+
+    const result = await getOrCreateCustomer("u1", "a@b.com");
+    expect(result).toBe("cus_existing");
+    expect(stripe.customers.create).not.toHaveBeenCalled();
+  });
+
+  it("creates a new Stripe customer when no stripeCustomerId", async () => {
+    (db.select as ReturnType<typeof vi.fn>).mockReturnValue({
+      from: vi.fn().mockReturnValue({
+        where: vi.fn().mockReturnValue({
+          limit: vi.fn().mockResolvedValue([
+            { id: "u1", email: "a@b.com", stripeCustomerId: null },
+          ]),
+        }),
+      }),
+    });
+
+    (stripe.customers.create as ReturnType<typeof vi.fn>).mockResolvedValue({ id: "cus_new" });
+
+    (db.update as ReturnType<typeof vi.fn>).mockReturnValue({
+      set: vi.fn().mockReturnValue({
+        where: vi.fn().mockResolvedValue([{ id: "u1" }]),
+      }),
+    });
+
+    const result = await getOrCreateCustomer("u1", "a@b.com");
+    expect(result).toBe("cus_new");
+    expect(stripe.customers.create).toHaveBeenCalledWith({
+      email: "a@b.com",
+      metadata: { userId: "u1" },
+    });
+  });
+
+  it("throws NOT_FOUND for missing user", async () => {
+    (db.select as ReturnType<typeof vi.fn>).mockReturnValue({
+      from: vi.fn().mockReturnValue({
+        where: vi.fn().mockReturnValue({
+          limit: vi.fn().mockResolvedValue([]),
+        }),
+      }),
+    });
+
+    await expect(getOrCreateCustomer("u-missing", "x@y.com")).rejects.toThrow(
+      "User not found",
+    );
+  });
+});
+
+describe("createCheckoutSession", () => {
+  it("creates a Stripe checkout session and returns URL", async () => {
+    (db.select as ReturnType<typeof vi.fn>).mockReturnValue({
+      from: vi.fn().mockReturnValue({
+        where: vi.fn().mockReturnValue({
+          limit: vi.fn().mockResolvedValue([
+            { id: "u1", email: "a@b.com", stripeCustomerId: "cus_123" },
+          ]),
+        }),
+      }),
+    });
+
+    (stripe.checkout.sessions.create as ReturnType<typeof vi.fn>).mockResolvedValue({
+      url: "https://checkout.stripe.com/session_123",
+      id: "session_123",
+    });
+
+    const result = await createCheckoutSession(
+      "u1",
+      "a@b.com",
+      "price_basic",
+      "https://example.com/success",
+      "https://example.com/cancel",
+    );
+
+    expect(result.url).toBe("https://checkout.stripe.com/session_123");
+    expect(result.sessionId).toBe("session_123");
+  });
+});
+
+describe("createPortalSession", () => {
+  it("creates a Stripe billing portal session", async () => {
+    (stripe.billingPortal.sessions.create as ReturnType<typeof vi.fn>).mockResolvedValue({
+      url: "https://billing.stripe.com/portal/session_456",
+    });
+
+    const result = await createPortalSession(
+      "cus_123",
+      "https://example.com/return",
+    );
+
+    expect(result.url).toBe("https://billing.stripe.com/portal/session_456");
+  });
+});
+
+describe("cancelSubscription", () => {
+  it("sets cancel_at_period_end on Stripe subscription", async () => {
+    (stripe.subscriptions.update as ReturnType<typeof vi.fn>).mockResolvedValue({});
+    (db.update as ReturnType<typeof vi.fn>).mockReturnValue({
+      set: vi.fn().mockReturnValue({
+        where: vi.fn().mockResolvedValue([]),
+      }),
+    });
+
+    const result = await cancelSubscription("sub_123");
+    expect(result.cancelAtPeriodEnd).toBe(true);
+    expect(stripe.subscriptions.update).toHaveBeenCalledWith("sub_123", {
+      cancel_at_period_end: true,
+    });
+  });
+});
+
+describe("reactivateSubscription", () => {
+  it("removes cancel_at_period_end on Stripe subscription", async () => {
+    (stripe.subscriptions.update as ReturnType<typeof vi.fn>).mockResolvedValue({});
+    (db.update as ReturnType<typeof vi.fn>).mockReturnValue({
+      set: vi.fn().mockReturnValue({
+        where: vi.fn().mockResolvedValue([]),
+      }),
+    });
+
+    const result = await reactivateSubscription("sub_123");
+    expect(result.cancelAtPeriodEnd).toBe(false);
+    expect(stripe.subscriptions.update).toHaveBeenCalledWith("sub_123", {
+      cancel_at_period_end: false,
+    });
+  });
+});
+
+describe("listInvoices", () => {
+  it("returns invoices list from Stripe", async () => {
+    (stripe.invoices.list as ReturnType<typeof vi.fn>).mockResolvedValue({
+      data: [{ id: "in_1" }, { id: "in_2" }],
+      has_more: false,
+    });
+
+    const result = await listInvoices("cus_123", 10);
+    expect(result.invoices).toHaveLength(2);
+    expect(result.hasMore).toBe(false);
+  });
+});
+
+describe("handleWebhookEvent", () => {
+  it("handles checkout.session.completed", async () => {
+    (db.insert as ReturnType<typeof vi.fn>).mockReturnValue({
+      values: vi.fn().mockReturnValue({
+        onConflictDoNothing: vi.fn().mockResolvedValue(undefined),
+      }),
+    });
+
+    (stripe.subscriptions.retrieve as ReturnType<typeof vi.fn>).mockResolvedValue({
+      id: "sub_new",
+      items: { data: [{ price: { id: "price_premium" } }] },
+      current_period_start: 1700000000,
+      current_period_end: 1702592000,
+      status: "active",
+      cancel_at_period_end: false,
+    });
+
+    await handleWebhookEvent({
+      type: "checkout.session.completed",
+      data: {
+        object: {
+          metadata: { userId: "u1" },
+          subscription: "sub_new",
+        },
+      },
+    } as never);
+
+    expect(db.insert).toHaveBeenCalled();
+  });
+
+  it("handles invoice.paid", async () => {
+    (db.select as ReturnType<typeof vi.fn>).mockReturnValue({
+      from: vi.fn().mockReturnValue({
+        where: vi.fn().mockReturnValue({
+          limit: vi.fn().mockResolvedValue([{ id: "sub_db_1" }]),
+        }),
+      }),
+    });
+
+    (db.update as ReturnType<typeof vi.fn>).mockReturnValue({
+      set: vi.fn().mockReturnValue({
+        where: vi.fn().mockReturnValue({
+          returning: vi.fn().mockResolvedValue([{ id: "sub_db_1", status: "active" }]),
+        }),
+      }),
+    });
+
+    await handleWebhookEvent({
+      type: "invoice.paid",
+      data: {
+        object: {
+          subscription: "sub_123",
+        },
+      },
+    } as never);
+  });
+
+  it("handles invoice.payment_failed", async () => {
+    (db.select as ReturnType<typeof vi.fn>).mockReturnValue({
+      from: vi.fn().mockReturnValue({
+        where: vi.fn().mockReturnValue({
+          limit: vi.fn().mockResolvedValue([{ id: "sub_db_1" }]),
+        }),
+      }),
+    });
+
+    (db.update as ReturnType<typeof vi.fn>).mockReturnValue({
+      set: vi.fn().mockReturnValue({
+        where: vi.fn().mockReturnValue({
+          returning: vi.fn().mockResolvedValue([{ id: "sub_db_1", status: "past_due" }]),
+        }),
+      }),
+    });
+
+    await handleWebhookEvent({
+      type: "invoice.payment_failed",
+      data: {
+        object: {
+          subscription: "sub_123",
+        },
+      },
+    } as never);
+  });
+
+  it("handles customer.subscription.updated", async () => {
+    (db.query.subscriptions.findFirst as ReturnType<typeof vi.fn>).mockResolvedValue(null);
+    (db.select as ReturnType<typeof vi.fn>).mockReturnValue({
+      from: vi.fn().mockReturnValue({
+        where: vi.fn().mockReturnValue({
+          limit: vi.fn().mockResolvedValue([]),
+        }),
+      }),
+    });
+
+    (db.update as ReturnType<typeof vi.fn>).mockReturnValue({
+      set: vi.fn().mockReturnValue({
+        where: vi.fn().mockReturnValue({
+          returning: vi.fn().mockResolvedValue([{ id: "sub_db_1", status: "active" }]),
+        }),
+      }),
+    });
+
+    await handleWebhookEvent({
+      type: "customer.subscription.updated",
+      data: {
+        object: {
+          id: "sub_123",
+          metadata: { userId: "u1" },
+          items: { data: [{ price: { id: "price_plus" } }] },
+          current_period_start: 1700000000,
+          current_period_end: 1702592000,
+          status: "active",
+          cancel_at_period_end: false,
+        },
+      },
+    } as never);
+  });
+
+  it("handles customer.subscription.deleted", async () => {
+    (db.select as ReturnType<typeof vi.fn>).mockReturnValue({
+      from: vi.fn().mockReturnValue({
+        where: vi.fn().mockReturnValue({
+          limit: vi.fn().mockResolvedValue([{ id: "sub_db_1" }]),
+        }),
+      }),
+    });
+
+    (db.update as ReturnType<typeof vi.fn>).mockReturnValue({
+      set: vi.fn().mockReturnValue({
+        where: vi.fn().mockReturnValue({
+          returning: vi.fn().mockResolvedValue([{ id: "sub_db_1", status: "canceled" }]),
+        }),
+      }),
+    });
+
+    await handleWebhookEvent({
+      type: "customer.subscription.deleted",
+      data: {
+        object: {
+          id: "sub_123",
+        },
+      },
+    } as never);
+  });
+});
diff --git a/web/src/server/services/billing.service.ts b/web/src/server/services/billing.service.ts
new file mode 100644
index 0000000..08dba7c
--- /dev/null
+++ b/web/src/server/services/billing.service.ts
@@ -0,0 +1,235 @@
+import { TRPCError } from "@trpc/server";
+import { eq } from "drizzle-orm";
+import { db } from "~/server/db";
+import { stripe } from "~/server/stripe";
+import { users } from "~/server/db/schema/auth";
+import { subscriptions } from "~/server/db/schema/subscription";
+import type Stripe from "stripe";
+
+type Tier = "basic" | "plus" | "premium";
+
+export async function getOrCreateCustomer(userId: string, email: string) {
+  const [user] = await db
+    .select()
+    .from(users)
+    .where(eq(users.id, userId))
+    .limit(1);
+
+  if (!user) {
+    throw new TRPCError({ code: "NOT_FOUND", message: "User not found" });
+  }
+
+  if (user.stripeCustomerId) {
+    return user.stripeCustomerId;
+  }
+
+  const customer = await stripe.customers.create({
+    email,
+    metadata: { userId },
+  });
+
+  await db
+    .update(users)
+    .set({ stripeCustomerId: customer.id })
+    .where(eq(users.id, userId));
+
+  return customer.id;
+}
+
+export async function createCheckoutSession(
+  userId: string,
+  email: string,
+  priceId: string,
+  successUrl: string,
+  cancelUrl: string,
+) {
+  const customerId = await getOrCreateCustomer(userId, email);
+
+  const session = await stripe.checkout.sessions.create({
+    customer: customerId,
+    mode: "subscription",
+    line_items: [{ price: priceId, quantity: 1 }],
+    success_url: successUrl,
+    cancel_url: cancelUrl,
+    metadata: { userId },
+  });
+
+  return { url: session.url, sessionId: session.id };
+}
+
+export async function createPortalSession(customerId: string, returnUrl: string) {
+  const session = await stripe.billingPortal.sessions.create({
+    customer: customerId,
+    return_url: returnUrl,
+  });
+
+  return { url: session.url };
+}
+
+export async function cancelSubscription(stripeSubscriptionId: string) {
+  await stripe.subscriptions.update(stripeSubscriptionId, {
+    cancel_at_period_end: true,
+  });
+
+  await db
+    .update(subscriptions)
+    .set({ cancelAtPeriodEnd: true })
+    .where(eq(subscriptions.stripeId, stripeSubscriptionId));
+
+  return { cancelAtPeriodEnd: true };
+}
+
+export async function reactivateSubscription(stripeSubscriptionId: string) {
+  await stripe.subscriptions.update(stripeSubscriptionId, {
+    cancel_at_period_end: false,
+  });
+
+  await db
+    .update(subscriptions)
+    .set({ cancelAtPeriodEnd: false })
+    .where(eq(subscriptions.stripeId, stripeSubscriptionId));
+
+  return { cancelAtPeriodEnd: false };
+}
+
+export async function listInvoices(
+  customerId: string,
+  limit: number = 10,
+  startingAfter?: string,
+) {
+  const params: Stripe.InvoiceListParams = {
+    customer: customerId,
+    limit,
+  };
+  if (startingAfter) {
+    params.starting_after = startingAfter;
+  }
+
+  const invoices = await stripe.invoices.list(params);
+  return {
+    invoices: invoices.data,
+    hasMore: invoices.has_more,
+  };
+}
+
+export async function updateSubscriptionInDB(
+  stripeId: string,
+  data: {
+    tier?: Tier;
+    status?: string;
+    currentPeriodStart?: Date;
+    currentPeriodEnd?: Date;
+    cancelAtPeriodEnd?: boolean;
+  },
+) {
+  const [existing] = await db
+    .select()
+    .from(subscriptions)
+    .where(eq(subscriptions.stripeId, stripeId))
+    .limit(1);
+
+  if (existing) {
+    const [updated] = await db
+      .update(subscriptions)
+      .set(data as Record<string, unknown>)
+      .where(eq(subscriptions.stripeId, stripeId))
+      .returning();
+    return updated;
+  }
+
+  return null;
+}
+
+export async function handleWebhookEvent(event: Stripe.Event) {
+  const obj = event.data.object as unknown as Record<string, unknown>;
+
+  switch (event.type) {
+    case "checkout.session.completed": {
+      const session = obj as unknown as Stripe.Checkout.Session;
+      const userId = session.metadata?.userId;
+      if (!userId || !session.subscription) break;
+
+      const stripeSub = await stripe.subscriptions.retrieve(
+        session.subscription as string,
+      );
+      const sub = stripeSub as unknown as Record<string, unknown>;
+
+      await db.insert(subscriptions).values({
+        userId,
+        stripeId: stripeSub.id,
+        tier: mapStripeProductToTier(
+          stripeSub.items.data[0]?.price?.id ?? "",
+        ),
+        status: sub.status as typeof subscriptions.$inferSelect.status,
+        currentPeriodStart: new Date((sub.current_period_start as number) * 1000),
+        currentPeriodEnd: new Date((sub.current_period_end as number) * 1000),
+        cancelAtPeriodEnd: sub.cancel_at_period_end as boolean,
+      }).onConflictDoNothing();
+      break;
+    }
+
+    case "invoice.paid": {
+      const invoice = obj;
+      if (!invoice.subscription) break;
+
+      await updateSubscriptionInDB(invoice.subscription as string, {
+        status: "active",
+      });
+      break;
+    }
+
+    case "invoice.payment_failed": {
+      const invoice = obj;
+      if (!invoice.subscription) break;
+
+      await updateSubscriptionInDB(invoice.subscription as string, {
+        status: "past_due",
+      });
+      break;
+    }
+
+    case "customer.subscription.updated": {
+      const stripeSub = obj as unknown as Stripe.Subscription;
+      const userId = stripeSub.metadata?.userId;
+      const sub = stripeSub as unknown as Record<string, unknown>;
+
+      if (!userId) {
+        const [existingSub] = await db
+          .select()
+          .from(subscriptions)
+          .where(eq(subscriptions.stripeId, stripeSub.id))
+          .limit(1);
+
+        if (!existingSub) break;
+      }
+
+      const tier = stripeSub.items.data[0]?.price?.id
+        ? mapStripeProductToTier(stripeSub.items.data[0].price.id)
+        : undefined;
+
+      await updateSubscriptionInDB(stripeSub.id, {
+        tier,
+        status: sub.status as string,
+        currentPeriodStart: new Date((sub.current_period_start as number) * 1000),
+        currentPeriodEnd: new Date((sub.current_period_end as number) * 1000),
+        cancelAtPeriodEnd: sub.cancel_at_period_end as boolean,
+      });
+      break;
+    }
+
+    case "customer.subscription.deleted": {
+      const stripeSub = obj as unknown as Stripe.Subscription;
+      await updateSubscriptionInDB(stripeSub.id, {
+        status: "canceled",
+      });
+      break;
+    }
+  }
+}
+
+function mapStripeProductToTier(priceId: string): Tier {
+  if (priceId === process.env.STRIPE_PRICE_BASIC) return "basic";
+  if (priceId === process.env.STRIPE_PRICE_PLUS) return "plus";
+  if (priceId === process.env.STRIPE_PRICE_PREMIUM) return "premium";
+  return "basic";
+}
diff --git a/web/src/server/stripe.ts b/web/src/server/stripe.ts
new file mode 100644
index 0000000..0cf0594
--- /dev/null
+++ b/web/src/server/stripe.ts
@@ -0,0 +1,6 @@
+import Stripe from "stripe";
+
+export const stripe = new Stripe(process.env.STRIPE_SECRET_KEY ?? "", {
+  apiVersion: "2026-04-22.dahlia" as const,
+  typescript: true,
+});