diff --git a/apps/api/src/lib/helpers.ts b/apps/api/src/lib/helpers.ts
index b3ecac7..660adea 100644
--- a/apps/api/src/lib/helpers.ts
+++ b/apps/api/src/lib/helpers.ts
@@ -83,6 +83,37 @@ export async function createHouseholdWithDefaults(
   return { id: household!.id, name: household!.name };
 }
 
+/** När en användare går med i ett annat hushåll: ta bort deras auto-skapade
+ * sol-hushåll (enda ägaren, inget lager) så det delade blir aktivt. */
+export async function discardEmptySoloHouseholds(
+  db: Database,
+  userId: string,
+  keepHouseholdId: string,
+): Promise<void> {
+  const memberships = await db
+    .select({
+      householdId: schema.householdMembers.householdId,
+      role: schema.householdMembers.role,
+    })
+    .from(schema.householdMembers)
+    .where(eq(schema.householdMembers.userId, userId));
+  for (const m of memberships) {
+    if (m.householdId === keepHouseholdId || m.role !== "owner") continue;
+    const members = await db
+      .select({ userId: schema.householdMembers.userId })
+      .from(schema.householdMembers)
+      .where(eq(schema.householdMembers.householdId, m.householdId));
+    if (members.length !== 1) continue; // inte ensam medlem → rör inte
+    const [inv] = await db
+      .select({ id: schema.inventoryItems.id })
+      .from(schema.inventoryItems)
+      .where(eq(schema.inventoryItems.householdId, m.householdId))
+      .limit(1);
+    if (inv) continue; // har lager → rör inte
+    await db.delete(schema.households).where(eq(schema.households.id, m.householdId)); // cascade städar medlem + platser
+  }
+}
+
 /** Hämta användarens aktiva hushåll (första medlemskapet) eller null. */
 export async function getActiveHouseholdId(db: Database, userId: string): Promise<string | null> {
   const [member] = await db
diff --git a/apps/api/src/routes/households.ts b/apps/api/src/routes/households.ts
index f572c34..b349fe2 100644
--- a/apps/api/src/routes/households.ts
+++ b/apps/api/src/routes/households.ts
@@ -16,6 +16,7 @@ import { errors, parse } from "../lib/errors.js";
 import {
   audit,
   createHouseholdWithDefaults,
+  discardEmptySoloHouseholds,
   emitEvent,
   generateInviteCode,
   requireMembership,
@@ -142,6 +143,8 @@ export async function householdRoutes(app: FastifyInstance) {
       .values({ householdId: household.id, userId: req.userId, role: "adult" })
       .onConflictDoNothing();
 
+    await discardEmptySoloHouseholds(app.db, req.userId, household.id);
+
     await emitEvent(app.db, {
       type: "HOUSEHOLD_MEMBER_ADDED",
       payload: { householdId: household.id, newUserId: req.userId, role: "adult" },
diff --git a/apps/api/src/routes/onboarding.ts b/apps/api/src/routes/onboarding.ts
index 3920453..96f7825 100644
--- a/apps/api/src/routes/onboarding.ts
+++ b/apps/api/src/routes/onboarding.ts
@@ -4,7 +4,12 @@ import { z } from "zod";
 import { schema } from "@app/database";
 import { quickStartInputSchema, onboardingInputSchema } from "@app/validation";
 import { errors, parse } from "../lib/errors.js";
-import { audit, createHouseholdWithDefaults, getActiveHouseholdId } from "../lib/helpers.js";
+import {
+  audit,
+  createHouseholdWithDefaults,
+  discardEmptySoloHouseholds,
+  getActiveHouseholdId,
+} from "../lib/helpers.js";
 
 import { t } from "../lib/i18n.js";
 import { KNOWN_FLAGS } from "@app/feature-flags";
@@ -171,6 +176,7 @@ export async function onboardingRoutes(app: FastifyInstance) {
         .insert(schema.householdMembers)
         .values({ householdId: household.id, userId: req.userId, role: "adult" })
         .onConflictDoNothing();
+      await discardEmptySoloHouseholds(app.db, req.userId, household.id);
       householdId = household.id;
     }