JavaScript Date setUTCSeconds() Method

What You’ll Learn

setUTCSeconds() writes the second (0–59) on a Date in UTC, with optional milliseconds. This guide covers syntax, minute snaps, combined second/ms overload, overflow, and comparisons with local setSeconds().

Introduction

ISO timestamps and server logs often need precise UTC second fields. After reading the UTC second with getUTCSeconds(), setUTCSeconds() writes it back without local timezone offsets.

Like setSeconds(), it mutates the Date and returns epoch milliseconds. Use UTC getters and setters together—do not mix local setSeconds with UTC getUTCSeconds in one step.

Understanding the setUTCSeconds() Method

Date.prototype.setUTCSeconds(second [, millisecond]) accepts a UTC second and an optional UTC millisecond. When you pass only the second, UTC milliseconds stay the same unless overflow normalization rolls the clock.

Verify results with toISOString() or UTC getters. For a full UTC time including ms in one call, use setUTCHours(h, m, s, ms) or setUTCMinutes(m, s, ms).

📝 Syntax

dateObj.setUTCSeconds(second)
dateObj.setUTCSeconds(second, millisecond)

Parameters

• second — Integer 0–59 in UTC time (overflow normalizes).
• millisecond (optional) — 0–999 UTC.

Return value

• Updated epoch milliseconds after the change.
• NaN if the Date was invalid before the call.

Examples Gallery

Open DevTools Console (F12) or use Try-it links. Examples use Date.UTC() for predictable UTC times.

const date = new Date(Date.UTC(2026, 2, 1, 12, 15, 5));
date.setUTCSeconds(30);

console.log(date.getUTCMinutes());  // 15
console.log(date.getUTCSeconds());  // 30
console.log(date.toISOString());    // "2026-03-01T12:15:30.000Z"

15
30
2026-03-01T12:15:30.000Z

const date = new Date(Date.UTC(2026, 2, 1, 12, 15, 42, 750));
date.setUTCSeconds(0, 0);

console.log(date.getUTCMinutes());         // 15
console.log(date.getUTCSeconds());         // 0
console.log(date.getUTCMilliseconds());    // 0
console.log(date.toISOString());           // "2026-03-01T12:15:00.000Z"

15
0
0
2026-03-01T12:15:00.000Z

const date = new Date(Date.UTC(2026, 2, 1, 9, 0, 0, 0));
date.setUTCSeconds(45, 500);

console.log(date.getUTCSeconds());         // 45
console.log(date.getUTCMilliseconds());    // 500
console.log(date.toISOString());           // "2026-03-01T09:00:45.500Z"

45
500
2026-03-01T09:00:45.500Z

const original = new Date(Date.UTC(2026, 2, 1, 12, 15, 10));
const adjusted = new Date(original);
adjusted.setUTCSeconds(55);

console.log("Original s:", original.getUTCSeconds());  // 10
console.log("Adjusted s:", adjusted.getUTCSeconds());  // 55

Original s: 10
Adjusted s: 55

const date = new Date(Date.UTC(2026, 2, 1, 12, 30, 45));
date.setUTCSeconds(90);

console.log(date.getUTCMinutes());  // 31
console.log(date.getUTCSeconds());  // 30

31
30

🚀 Common Use Cases

• UTC log alignment — setUTCSeconds(0, 0) for minute buckets.
• ISO timestamps — apply second/ms from parsed UTC strings.
• Test fixtures — pin exact UTC second/ms with Date.UTC().
• Cron alignment — snap events to :00 at UTC minute boundaries.
• API sync — align server timestamps to UTC second precision.
• Clone + mutate — keep originals when tweaking sub-minute UTC fields.

📝 Notes

• setUTCSeconds() adjusts the second hand in UTC (0–59 typical range).
• Mutates the original Date—clone with new Date(date) when needed.
• Returns epoch ms, not the Date—no fluent chaining on the return value.
• Overflow normalizes (second 90 → next UTC minute + 30 seconds).
• Omitting the ms argument does not reset milliseconds to zero.
• Use setSeconds for local clocks; setUTCSeconds for ISO/server rules.

💡 Best Practices