diff --git a/src/lib/format.test.mjs b/src/lib/format.test.mjs
new file mode 100644
index 0000000..fe95b5c
--- /dev/null
+++ b/src/lib/format.test.mjs
@@ -0,0 +1,21 @@
+import assert from 'node:assert/strict';
+import test from 'node:test';
+
+import { formatPace } from './format.ts';
+
+test('carries rounded seconds into the next minute', () => {
+  assert.equal(formatPace(299.6, 1000), '5:00 /km');
+});
+
+test('zero-pads pace seconds', () => {
+  assert.equal(formatPace(305, 1000), '5:05 /km');
+});
+
+test('uses metric and imperial pace suffixes', () => {
+  assert.equal(formatPace(300, 1000, 'metric'), '5:00 /km');
+  assert.equal(formatPace(300, 1609.344, 'imperial'), '5:00 /mi');
+});
+
+test('keeps normal pace values unchanged', () => {
+  assert.equal(formatPace(272, 1000), '4:32 /km');
+});
diff --git a/src/lib/format.ts b/src/lib/format.ts
index c52f2f0..8e035d0 100644
--- a/src/lib/format.ts
+++ b/src/lib/format.ts
@@ -28,7 +28,8 @@ export function formatDuration(seconds: number): string {
 export function formatPace(seconds: number, meters: number, unit: DistanceUnit = 'metric'): string {
   if (meters <= 0) return '--';
   const perUnit = unit === 'imperial' ? (seconds / (meters / 1000 / KM_PER_MILE)) : seconds / (meters / 1000);
-  const m = Math.floor(perUnit / 60);
-  const s = Math.round(perUnit % 60);
+  const rounded = Math.round(perUnit);
+  const m = Math.floor(rounded / 60);
+  const s = rounded % 60;
   return `${m}:${String(s).padStart(2, '0')} /${unit === 'imperial' ? 'mi' : 'km'}`;
 }