diff --git a/src/lib/measurements/__tests__/drain-per-sample-cumulative.test.ts b/src/lib/measurements/__tests__/drain-per-sample-cumulative.test.ts
index d391105e5..260a9c5b3 100644
--- a/src/lib/measurements/__tests__/drain-per-sample-cumulative.test.ts
+++ b/src/lib/measurements/__tests__/drain-per-sample-cumulative.test.ts
@@ -1,5 +1,14 @@
 import { describe, expect, it, vi } from "vitest";
 
+// The SUM drain now recomputes the affected DAY rollup bucket after each
+// per-day fold (so a drained day's stale double-counted sum self-heals).
+// Mock it: these are pure-logic tests over a Prisma mock with no DB, and
+// the real recompute issues raw SQL against the singleton client.
+vi.mock("@/lib/rollups/measurement-rollups", () => ({
+  recomputeBucketsForMeasurement: vi.fn().mockResolvedValue(undefined),
+}));
+import { recomputeBucketsForMeasurement } from "@/lib/rollups/measurement-rollups";
+
 import {
   bucketRowsByUserDay,
   canonicalDailyTimestamp,
@@ -444,6 +453,26 @@ describe("drainPerSampleCumulative — late-sync fold into existing total", () =
     const createArg = create.mock.calls[0]?.[0] as { data: { value: number } };
     expect(createArg.data.value).toBe(500);
   });
+
+  it("recomputes the DAY rollup bucket for the drained day so the stale sum self-heals", async () => {
+    vi.mocked(recomputeBucketsForMeasurement).mockClear();
+    const { prisma } = buildFoldMock(null);
+
+    await drainPerSampleCumulative(prisma, { log: () => {} });
+
+    // Without this the rollup tier keeps serving the pre-drain
+    // double-counted sumValue forever (it reads only deleted_at IS NULL).
+    expect(recomputeBucketsForMeasurement).toHaveBeenCalledTimes(1);
+    const [userId, type, canonicalTs] = vi.mocked(
+      recomputeBucketsForMeasurement,
+    ).mock.calls[0]!;
+    expect(userId).toBe("user-1");
+    expect(type).toBe("ACTIVITY_STEPS");
+    // Canonical local-noon of the Berlin day 2026-05-16 (CEST, UTC+2).
+    expect((canonicalTs as Date).toISOString()).toBe(
+      "2026-05-16T10:00:00.000Z",
+    );
+  });
 });
 
 // Root cause of the v1.18.10 bloat: a single day whose mint collided with the
diff --git a/src/lib/measurements/consolidate-legacy-steps.ts b/src/lib/measurements/consolidate-legacy-steps.ts
index 4c3f8dc81..5ddfe1519 100644
--- a/src/lib/measurements/consolidate-legacy-steps.ts
+++ b/src/lib/measurements/consolidate-legacy-steps.ts
@@ -39,6 +39,7 @@
  */
 import type { PrismaClient } from "@/generated/prisma/client";
 import { isP2002 as isUniqueConstraintViolation } from "@/lib/prisma-errors";
+import { recomputeBucketsForMeasurement } from "@/lib/rollups/measurement-rollups";
 
 import { dailyStatsExternalId } from "./apple-health-mapping";
 import {
@@ -259,6 +260,16 @@ export async function consolidateLegacySteps(
           });
           removed = del.count;
         });
+
+        // Re-aggregate the affected (user, type, day) rollup bucket after the
+        // soft-delete commits. The legacy granular rows that just dropped out
+        // of the live read were being summed alongside any existing daily-stats
+        // total, so the DAY rollup bucket carried a double-counted total. The
+        // rollup tier reads only `deleted_at IS NULL`; without this recompute
+        // the stale bucket persists forever. Mirrors the mean drain's
+        // post-write recompute exactly.
+        await recomputeBucketsForMeasurement(userId, type, canonicalTimestamp);
+
         return { kind: "written", sourceRowsRemoved: removed };
       } catch (err) {
         // A pre-existing row can collide on the second unique index
diff --git a/src/lib/measurements/drain-per-sample-cumulative.ts b/src/lib/measurements/drain-per-sample-cumulative.ts
index 9bd92ca3b..319b42933 100644
--- a/src/lib/measurements/drain-per-sample-cumulative.ts
+++ b/src/lib/measurements/drain-per-sample-cumulative.ts
@@ -34,6 +34,7 @@
 import { Prisma } from "@/generated/prisma/client";
 import type { MeasurementType, PrismaClient } from "@/generated/prisma/client";
 import { isP2002 as isUniqueConstraintViolation } from "@/lib/prisma-errors";
+import { recomputeBucketsForMeasurement } from "@/lib/rollups/measurement-rollups";
 
 import {
   CUMULATIVE_HK_TYPES,
@@ -355,6 +356,15 @@ export async function drainPerSampleCumulative(
         if (!isUniqueConstraintViolation(err)) throw err;
         removed = await foldOnce();
       }
+
+      // Re-aggregate the affected (user, type, day) rollup bucket after the
+      // fold commits — the per-sample rows are now gone and the canonical
+      // daily-sum row is the only live reading. The rollup tier reads only
+      // `deleted_at IS NULL`, so without this the day's DAY bucket keeps the
+      // stale pre-drain (double-counted) sumValue forever and never
+      // self-heals. Mirrors the mean drain's post-write recompute exactly.
+      await recomputeBucketsForMeasurement(userId, type, canonicalTimestamp);
+
       return { kind: "written", sourceRowsRemoved: removed };
     },
     recordBucket: ({