diff --git a/src/utils/__tests__/formatRemaining.test.ts b/src/utils/__tests__/formatRemaining.test.ts
new file mode 100644
index 00000000..b1e8e5d4
--- /dev/null
+++ b/src/utils/__tests__/formatRemaining.test.ts
@@ -0,0 +1,143 @@
+import { describe, expect, it } from 'vitest';
+import { formatRemaining } from '../formatRemaining';
+
+const ONE_SECOND_MS = 1000;
+const ONE_MINUTE_MS = 60 * ONE_SECOND_MS;
+const ONE_HOUR_MS = 60 * ONE_MINUTE_MS;
+const ONE_DAY_MS = 24 * ONE_HOUR_MS;
+
+describe('formatRemaining', () => {
+  describe('matured case (diffMs <= 0)', () => {
+    it('returns matured status when current time equals maturity time', () => {
+      const baseTime = 1_700_000_000_000;
+      expect(formatRemaining(baseTime, baseTime)).toEqual({
+        text: 'Matured',
+        status: 'matured',
+      });
+    });
+
+    it('returns matured status when maturity time is in the past', () => {
+      const current = 1_700_000_000_000;
+      const maturity = current - 5 * ONE_MINUTE_MS;
+      expect(formatRemaining(maturity, current)).toEqual({
+        text: 'Matured',
+        status: 'matured',
+      });
+    });
+
+    it('uses Date.now by default when maturity timestamp is in the past', () => {
+      const pastTime = Date.now() - 10_000;
+      expect(formatRemaining(pastTime)).toEqual({
+        text: 'Matured',
+        status: 'matured',
+      });
+    });
+  });
+
+  describe('threshold boundaries', () => {
+    const current = 1_700_000_000_000;
+
+    it('returns critical status when remaining time is exactly one day', () => {
+      const maturity = current + ONE_DAY_MS;
+      expect(formatRemaining(maturity, current)).toEqual({
+        text: '1d 0h 0m',
+        status: 'critical',
+      });
+    });
+
+    it('returns critical status when remaining time is less than one day', () => {
+      const maturity = current + ONE_DAY_MS - 1;
+      expect(formatRemaining(maturity, current)).toEqual({
+        text: '23h 59m',
+        status: 'critical',
+      });
+    });
+
+    it('returns critical status for small remaining durations under one hour', () => {
+      const maturity = current + 30 * ONE_MINUTE_MS;
+      expect(formatRemaining(maturity, current)).toEqual({
+        text: '30m',
+        status: 'critical',
+      });
+    });
+
+    it('returns warning status when remaining time is slightly greater than one day', () => {
+      const maturity = current + ONE_DAY_MS + 1;
+      expect(formatRemaining(maturity, current)).toEqual({
+        text: '1d 0h 0m',
+        status: 'warning',
+      });
+    });
+
+    it('returns warning status when remaining time is between one and seven days', () => {
+      const maturity = current + 3 * ONE_DAY_MS + 4 * ONE_HOUR_MS + 15 * ONE_MINUTE_MS;
+      expect(formatRemaining(maturity, current)).toEqual({
+        text: '3d 4h 15m',
+        status: 'warning',
+      });
+    });
+
+    it('returns warning status when remaining time is exactly seven days', () => {
+      const maturity = current + 7 * ONE_DAY_MS;
+      expect(formatRemaining(maturity, current)).toEqual({
+        text: '7d 0h 0m',
+        status: 'warning',
+      });
+    });
+
+    it('returns healthy status when remaining time is strictly greater than seven days', () => {
+      const maturity = current + 7 * ONE_DAY_MS + 1;
+      expect(formatRemaining(maturity, current)).toEqual({
+        text: '7d 0h 0m',
+        status: 'healthy',
+      });
+    });
+
+    it('returns healthy status for long remaining durations', () => {
+      const maturity = current + 14 * ONE_DAY_MS + 2 * ONE_HOUR_MS + 5 * ONE_MINUTE_MS;
+      expect(formatRemaining(maturity, current)).toEqual({
+        text: '14d 2h 5m',
+        status: 'healthy',
+      });
+    });
+  });
+
+  describe('formatting branches (lines 33-35)', () => {
+    const current = 1_700_000_000_000;
+
+    it('includes days prefix and hours when days > 0 and hours > 0', () => {
+      const maturity = current + 4 * ONE_DAY_MS + 6 * ONE_HOUR_MS + 20 * ONE_MINUTE_MS;
+      const result = formatRemaining(maturity, current);
+      expect(result.text).toBe('4d 6h 20m');
+      expect(result.status).toBe('warning');
+    });
+
+    it('includes 0h when days > 0 and hours === 0', () => {
+      const maturity = current + 2 * ONE_DAY_MS + 45 * ONE_MINUTE_MS;
+      const result = formatRemaining(maturity, current);
+      expect(result.text).toBe('2d 0h 45m');
+      expect(result.status).toBe('warning');
+    });
+
+    it('omits days and includes hours when days === 0 and hours > 0', () => {
+      const maturity = current + 5 * ONE_HOUR_MS + 12 * ONE_MINUTE_MS;
+      const result = formatRemaining(maturity, current);
+      expect(result.text).toBe('5h 12m');
+      expect(result.status).toBe('critical');
+    });
+
+    it('omits days and hours when days === 0 and hours === 0', () => {
+      const maturity = current + 42 * ONE_MINUTE_MS;
+      const result = formatRemaining(maturity, current);
+      expect(result.text).toBe('42m');
+      expect(result.status).toBe('critical');
+    });
+
+    it('formats 0m when diff is less than one minute', () => {
+      const maturity = current + 45 * ONE_SECOND_MS;
+      const result = formatRemaining(maturity, current);
+      expect(result.text).toBe('0m');
+      expect(result.status).toBe('critical');
+    });
+  });
+});
diff --git a/src/utils/formatRemaining.ts b/src/utils/formatRemaining.ts
index 1dab7b9f..b04a3810 100644
--- a/src/utils/formatRemaining.ts
+++ b/src/utils/formatRemaining.ts
@@ -5,9 +5,16 @@ export interface RemainingMaturity {
   status: MaturityStatus;
 }
 
+/**
+ * Calculates human-readable remaining time until maturity and determines urgency status.
+ *
+ * @param maturityTimestamp - Target maturity epoch timestamp in milliseconds.
+ * @param currentTimestamp - Current epoch timestamp in milliseconds, defaulting to Date.now().
+ * @returns Object containing formatted remaining time string and urgency status.
+ */
 export const formatRemaining = (
   maturityTimestamp: number,
-  currentTimestamp: number = Date.now()
+  currentTimestamp: number = Date.now(),
 ): RemainingMaturity => {
   const diffMs = maturityTimestamp - currentTimestamp;
 
@@ -29,7 +36,7 @@ export const formatRemaining = (
     status = 'warning';
   }
 
-  const timeParts = [];
+  const timeParts: string[] = [];
   if (days > 0) timeParts.push(`${days}d`);
   if (hours > 0 || days > 0) timeParts.push(`${hours}h`);
   timeParts.push(`${minutes}m`);
@@ -38,4 +45,4 @@ export const formatRemaining = (
     text: timeParts.join(' '),
     status,
   };
-};
\ No newline at end of file
+};