diff --git a/apps/mobile/src/features/usage/UsageRouteScreen.tsx b/apps/mobile/src/features/usage/UsageRouteScreen.tsx
index 817e6d7f9543..6086d4c39f72 100644
--- a/apps/mobile/src/features/usage/UsageRouteScreen.tsx
+++ b/apps/mobile/src/features/usage/UsageRouteScreen.tsx
@@ -9,6 +9,7 @@ import {
   formatPercent,
   formatTokens,
   formatUsd,
+  makeMonthToDateWindow,
   makeWindow,
 } from "@t3tools/shared/usageFormat";
 import { useMemo, useState } from "react";
@@ -25,24 +26,32 @@ import type { UsageChartMetric } from "./usageChartData";
 import { PROVIDER_LABEL, useProviderColors } from "./usageProviders";
 
 const WINDOW_OPTIONS = [
-  { days: 1, label: "Past 24h" },
-  { days: 7, label: "7 days" },
-  { days: 30, label: "30 days" },
-  { days: 90, label: "90 days" },
+  { value: 1, label: "Past 24h" },
+  { value: 7, label: "7 days" },
+  { value: "mtd", label: "MTD" },
+  { value: 30, label: "30 days" },
+  { value: 90, label: "90 days" },
 ] as const;
 
+type WindowPeriod = (typeof WINDOW_OPTIONS)[number]["value"];
+
+function makeWindowForPeriod(period: WindowPeriod) {
+  if (period === "mtd") return makeMonthToDateWindow();
+  return makeWindow(period, undefined, period === 1 ? "hour" : "day");
+}
+
 const CHART_HEIGHT = 180;
 
 export function UsageRouteScreen() {
   const navigation = useNavigation();
   const insets = useSafeAreaInsets();
   const [windowSelection, setWindowSelection] = useState(() => ({
-    days: 30,
+    period: 30 as WindowPeriod,
     window: makeWindow(30),
   }));
   const [metric, setMetric] = useState<UsageChartMetric>("cost");
-  const { days: windowDays, window } = windowSelection;
-  const isPast24Hours = windowDays === 1;
+  const { period: windowPeriod, window } = windowSelection;
+  const isPast24Hours = windowPeriod === 1;
   const { merged, environments, isPending, isPartial, refresh } = useUsage(window);
 
   const days = useMemo(
@@ -73,14 +82,14 @@ export function UsageRouteScreen() {
   // before. The initial scan renders its own placeholder, and an unreachable
   // environment stays pending forever — neither may pin the spinner on.
   const refreshing = environments.some((entry) => entry.isPending && entry.summary !== null);
-  const selectWindow = (days: number) => {
+  const selectWindow = (period: WindowPeriod) => {
     setWindowSelection({
-      days,
-      window: makeWindow(days, undefined, days === 1 ? "hour" : "day"),
+      period,
+      window: makeWindowForPeriod(period),
     });
   };
   const refreshWindow = () => {
-    const nextWindow = makeWindow(windowDays, undefined, isPast24Hours ? "hour" : "day");
+    const nextWindow = makeWindowForPeriod(windowPeriod);
     if (
       nextWindow.sinceDay === window.sinceDay &&
       nextWindow.untilDay === window.untilDay &&
@@ -89,7 +98,7 @@ export function UsageRouteScreen() {
     ) {
       refresh();
     } else {
-      setWindowSelection({ days: windowDays, window: nextWindow });
+      setWindowSelection({ period: windowPeriod, window: nextWindow });
     }
   };
 
@@ -110,8 +119,8 @@ export function UsageRouteScreen() {
         refreshControl={<RefreshControl refreshing={refreshing} onRefresh={refreshWindow} />}
       >
         <SegmentedControl
-          options={WINDOW_OPTIONS.map((option) => ({ value: option.days, label: option.label }))}
-          selected={windowDays}
+          options={WINDOW_OPTIONS}
+          selected={windowPeriod}
           onSelect={selectWindow}
         />
 
diff --git a/apps/web/src/components/usage/UsagePage.test.tsx b/apps/web/src/components/usage/UsagePage.test.tsx
index 8e86b521e890..92d353642bbb 100644
--- a/apps/web/src/components/usage/UsagePage.test.tsx
+++ b/apps/web/src/components/usage/UsagePage.test.tsx
@@ -16,7 +16,7 @@ vi.mock("react", async (importOriginal) => {
     useState: vi.fn((initial: unknown) => [
       typeof initial === "function"
         ? {
-            days: 1,
+            period: 1,
             window: {
               sinceDay: "2026-08-10",
               untilDay: "2026-08-11",
diff --git a/apps/web/src/components/usage/UsagePage.tsx b/apps/web/src/components/usage/UsagePage.tsx
index 7474bb9d6120..28ad74abcfc3 100644
--- a/apps/web/src/components/usage/UsagePage.tsx
+++ b/apps/web/src/components/usage/UsagePage.tsx
@@ -17,6 +17,7 @@ import {
   formatPercent,
   formatTokens,
   formatUsd,
+  makeMonthToDateWindow,
   makeWindow,
 } from "@t3tools/shared/usageFormat";
 import { Button } from "../ui/button";
@@ -35,21 +36,29 @@ import { UsageProviderChart, type UsageChartMetric } from "./UsageProviderChart"
 import { PROVIDER_ORDER, PROVIDER_PRESENTATION, providersWithUsage } from "./usageProviders";
 
 const WINDOW_OPTIONS = [
-  { days: 1, label: "Past 24h" },
-  { days: 7, label: "7 days" },
-  { days: 30, label: "30 days" },
-  { days: 90, label: "90 days" },
+  { value: 1, label: "Past 24h" },
+  { value: 7, label: "7 days" },
+  { value: "mtd", label: "MTD" },
+  { value: 30, label: "30 days" },
+  { value: 90, label: "90 days" },
 ] as const;
 
+type WindowPeriod = (typeof WINDOW_OPTIONS)[number]["value"];
+
+function makeWindowForPeriod(period: WindowPeriod) {
+  if (period === "mtd") return makeMonthToDateWindow();
+  return makeWindow(period, undefined, period === 1 ? "hour" : "day");
+}
+
 export function UsagePage() {
   const [windowSelection, setWindowSelection] = useState(() => ({
-    days: 30,
+    period: 30 as WindowPeriod,
     window: makeWindow(30),
   }));
   const [metric, setMetric] = useState<UsageChartMetric>("cost");
   const [breakdown, setBreakdown] = useState<"model" | "time">("model");
-  const { days: windowDays, window } = windowSelection;
-  const isPast24Hours = windowDays === 1;
+  const { period: windowPeriod, window } = windowSelection;
+  const isPast24Hours = windowPeriod === 1;
   const { merged, environments, isPending, isPartial, refresh } = useUsage(window);
 
   // Hold the content until every environment is terminal. Rendering merged
@@ -86,14 +95,14 @@ export function UsagePage() {
   const activeProviders = useMemo(() => providersWithUsage(merged.providers), [merged.providers]);
   const timeValueColumnWidth = `${60 / (activeProviders.length + 2)}%`;
 
-  const selectWindow = (days: number) => {
+  const selectWindow = (period: WindowPeriod) => {
     setWindowSelection({
-      days,
-      window: makeWindow(days, undefined, days === 1 ? "hour" : "day"),
+      period,
+      window: makeWindowForPeriod(period),
     });
   };
   const refreshWindow = () => {
-    const nextWindow = makeWindow(windowDays, undefined, isPast24Hours ? "hour" : "day");
+    const nextWindow = makeWindowForPeriod(windowPeriod);
     if (
       nextWindow.sinceDay === window.sinceDay &&
       nextWindow.untilDay === window.untilDay &&
@@ -102,7 +111,7 @@ export function UsagePage() {
     ) {
       refresh();
     } else {
-      setWindowSelection({ days: windowDays, window: nextWindow });
+      setWindowSelection({ period: windowPeriod, window: nextWindow });
     }
   };
   const windowLabel =
@@ -139,14 +148,15 @@ export function UsagePage() {
         <ToggleGroup
           aria-label="Usage period"
           variant="segmented"
-          value={[String(windowDays)]}
+          value={[String(windowPeriod)]}
           onValueChange={(next) => {
             const value = next[0];
-            if (value) selectWindow(Number(value));
+            const option = WINDOW_OPTIONS.find((candidate) => String(candidate.value) === value);
+            if (option) selectWindow(option.value);
           }}
         >
           {WINDOW_OPTIONS.map((option) => (
-            <Toggle key={option.days} value={String(option.days)}>
+            <Toggle key={option.value} value={String(option.value)}>
               {option.label}
             </Toggle>
           ))}
@@ -175,7 +185,13 @@ export function UsagePage() {
             <SelectItem value="tokens">Tokens</SelectItem>
           </SelectPopup>
         </Select>
-        <Select value={String(windowDays)} onValueChange={(value) => selectWindow(Number(value))}>
+        <Select
+          value={String(windowPeriod)}
+          onValueChange={(value) => {
+            const option = WINDOW_OPTIONS.find((candidate) => String(candidate.value) === value);
+            if (option) selectWindow(option.value);
+          }}
+        >
           <SelectTrigger
             aria-label="Usage period"
             size="compact"
@@ -183,12 +199,12 @@ export function UsagePage() {
             className="w-auto min-w-0"
           >
             <SelectValue>
-              {WINDOW_OPTIONS.find((option) => option.days === windowDays)?.label}
+              {WINDOW_OPTIONS.find((option) => option.value === windowPeriod)?.label}
             </SelectValue>
           </SelectTrigger>
           <SelectPopup align="end" alignItemWithTrigger={false}>
             {WINDOW_OPTIONS.map((option) => (
-              <SelectItem key={option.days} value={String(option.days)}>
+              <SelectItem key={option.value} value={String(option.value)}>
                 {option.label}
               </SelectItem>
             ))}
diff --git a/docs/user/usage.md b/docs/user/usage.md
index ff38c730c1cd..945d3ba591a1 100644
--- a/docs/user/usage.md
+++ b/docs/user/usage.md
@@ -9,5 +9,6 @@ Grok Build totals come from persisted session updates. Interactive turns that ne
 completed-turn record will not appear.
 
 Use **Past 24h** for an hourly chart covering the exact rolling 24-hour period. The **7 days**,
-**30 days**, and **90 days** ranges use daily resolution. Cost and token toggles update both the
-headline and chart, and refreshing rescans every connected environment.
+**30 days**, and **90 days** ranges use daily resolution. **MTD** covers the first day of the current
+month through today in your local time zone. Cost and token toggles update both the headline and
+chart, and refreshing rescans every connected environment.
diff --git a/packages/shared/src/usageFormat.test.ts b/packages/shared/src/usageFormat.test.ts
index fb231fbacb20..4c1183c83e32 100644
--- a/packages/shared/src/usageFormat.test.ts
+++ b/packages/shared/src/usageFormat.test.ts
@@ -6,6 +6,7 @@ import {
   formatDateTimeShort,
   formatHourShort,
   formatRelativeHourShort,
+  makeMonthToDateWindow,
   makeWindow,
 } from "./usageFormat.ts";
 
@@ -55,6 +56,26 @@ describe("hourly usage formatting", () => {
     expect(window.untilTime).toBe("2026-08-11T12:37:00.000Z");
   });
 
+  it("builds a month-to-date request in the viewer's time zone", () => {
+    const resolved = new Intl.DateTimeFormat().resolvedOptions();
+    const resolvedOptions = vi
+      .spyOn(Intl.DateTimeFormat.prototype, "resolvedOptions")
+      .mockReturnValue({ ...resolved, timeZone: "America/Los_Angeles" });
+
+    try {
+      const window = makeMonthToDateWindow(new Date("2026-09-01T06:30:00.000Z"));
+
+      expect(window).toMatchObject({
+        sinceDay: "2026-08-01",
+        untilDay: "2026-08-31",
+        timeZone: "America/Los_Angeles",
+        resolution: "day",
+      });
+    } finally {
+      resolvedOptions.mockRestore();
+    }
+  });
+
   it("degrades an unknown resolved zone to UTC instead of crashing", () => {
     const resolved = new Intl.DateTimeFormat().resolvedOptions();
     const resolvedOptions = vi
diff --git a/packages/shared/src/usageFormat.ts b/packages/shared/src/usageFormat.ts
index bd751829dd87..acea30126f64 100644
--- a/packages/shared/src/usageFormat.ts
+++ b/packages/shared/src/usageFormat.ts
@@ -230,3 +230,12 @@ export function makeWindow(
     resolution,
   };
 }
+
+/** The current calendar month through today in the viewer's own time zone. */
+export function makeMonthToDateWindow(now = new Date()): UsageSummaryInput {
+  const window = makeWindow(1, now);
+  return {
+    ...window,
+    sinceDay: UsageDay.make(`${window.untilDay.slice(0, 7)}-01`),
+  };
+}