diff --git a/src/lib/doctor-report/collect.ts b/src/lib/doctor-report/collect.ts
index 901a4f885..05fa74ec1 100644
--- a/src/lib/doctor-report/collect.ts
+++ b/src/lib/doctor-report/collect.ts
@@ -61,7 +61,7 @@ import { loadDenseMeasurementBuckets } from "./dense-buckets";
 import { summariseDenseBuckets } from "./measurement-series";
 import { emptyGlucoseClinical } from "./glucose-panel";
 import { buildAdministrationLedger, buildGlp1Block } from "./medications";
-import { validTimezoneOr, DEFAULT_TIMEZONE } from "@/lib/tz/format";
+import { userDayKey, validTimezoneOr, DEFAULT_TIMEZONE } from "@/lib/tz/format";
 import {
   loadAllergies,
   loadAnamnesis,
@@ -148,6 +148,12 @@ export async function collectDoctorReportData(
     },
   });
   const reportTz = validTimezoneOr(userProfile?.timezone, DEFAULT_TIMEZONE);
+  // `startsOn` / `endsOn` are calendar dates (stored as UTC midnight), so
+  // they compare against the window's first and last day in the report zone,
+  // not its instants: west of UTC the window starts hours after UTC midnight,
+  // and a course that ended on the first day read as over before it began.
+  const firstDay = new Date(`${userDayKey(start, reportTz)}T00:00:00.000Z`);
+  const lastDay = new Date(`${userDayKey(end, reportTz)}T00:00:00.000Z`);
 
   const aggregateDenseTypes = days > DENSE_REPORT_RAW_WINDOW_DAYS;
   const densePulse = aggregateDenseTypes && !excluded.includes("PULSE");
@@ -202,7 +208,7 @@ export async function collectDoctorReportData(
               AND: [
                 {
                   OR: [
-                    { startsOn: { lte: end } },
+                    { startsOn: { lte: lastDay } },
                     { startsOn: null, createdAt: { lte: end } },
                     {
                       intakeEvents: {
@@ -214,7 +220,7 @@ export async function collectDoctorReportData(
                     },
                   ],
                 },
-                { OR: [{ endsOn: null }, { endsOn: { gte: start } }] },
+                { OR: [{ endsOn: null }, { endsOn: { gte: firstDay } }] },
               ],
             },
             include: {
diff --git a/tests/integration/doctor-report-fixed-window.test.ts b/tests/integration/doctor-report-fixed-window.test.ts
index 72116145a..e42ceb95c 100644
--- a/tests/integration/doctor-report-fixed-window.test.ts
+++ b/tests/integration/doctor-report-fixed-window.test.ts
@@ -138,4 +138,46 @@ describe("doctor report with a fixed end date", () => {
     expect(glp1?.currentDose?.value).toBe(0.25);
     expect(glp1?.lastInjection?.date).toBe("2026-03-20T08:05:00.000Z");
   });
+  it("compares a course's start and end dates as days in the report zone", async () => {
+    // West of UTC the window's instants sit hours after UTC midnight, and the
+    // course dates are calendar days stored as UTC midnight.
+    const prisma = getPrismaClient();
+    const user = await prisma.user.create({
+      data: {
+        username: "west-window",
+        email: "west-window@example.test",
+        timezone: "America/New_York",
+      },
+    });
+    const course = (name: string, startsOn: string, endsOn: string | null) =>
+      prisma.medication.create({
+        data: {
+          userId: user.id,
+          name,
+          dose: "1 mg",
+          startsOn: new Date(`${startsOn}T00:00:00.000Z`),
+          endsOn: endsOn ? new Date(`${endsOn}T00:00:00.000Z`) : null,
+          createdAt: new Date("2025-06-01T00:00:00.000Z"),
+        },
+      });
+    await course("Ended on the first day", "2025-10-01", "2026-01-01");
+    await course("Ended the day before", "2025-10-01", "2025-12-31");
+    await course("Started on the last day", "2026-03-31", null);
+    await course("Started the day after", "2026-04-01", null);
+
+    const data = await collectDoctorReportData(
+      user.id,
+      {
+        start: new Date("2026-01-01T05:00:00.000Z"),
+        end: new Date("2026-04-01T03:59:59.999Z"),
+        days: 90,
+      },
+      selectionFromLeaves(ALL_LEAF_IDS),
+    );
+
+    expect(data.medications?.map((m) => m.name).sort()).toEqual([
+      "Ended on the first day",
+      "Started on the last day",
+    ]);
+  });
 });