What is a Unix Timestamp? How to Use Timestamps Correctly in Development

What is a Unix Timestamp?

A Unix timestamp (POSIX time / Epoch time) is the number of seconds elapsed since 1970-01-01 00:00:00 UTC — the Unix Epoch.

For example, 2026-04-01 00:00:00 UTC ≈ 1743465600 — about 1.7 billion seconds since the Epoch.

Why Use Timestamps?

1. Time-zone agnostic: Represents an absolute UTC moment — identical in Beijing, New York, and London. 2. Easy arithmetic:

``javascript

const sevenDaysAgo = Date.now() - 7 * 24 * 60 * 60 * 1000;

` 3. Storage efficiency: A 32-bit integer covers timestamps; more compact than strings with better index performance. 4. Easy comparison: Pure numbers — compare with > and < directly.

Seconds vs Milliseconds

The #1 source of timestamp bugs!

• Unix timestamp (seconds): 10 digits — 1743465600
• JavaScript timestamp (ms): 13 digits — 1743465600000

Best practice: label precision in field names — e.g. created_at_ms or created_at_sec.

Working with Timestamps in JavaScript

`javascript

// Current ms timestamp

const msTs = Date.now(); // 1743465600000

// Current second timestamp

const secTs = Math.floor(Date.now() / 1000); // 1743465600

// Timestamp → Date (JS needs ms)

const date = new Date(1743465600 * 1000); // multiply by 1000!

// Format for local timezone (Beijing)

const str = date.toLocaleString('zh-CN', { timeZone: 'Asia/Shanghai' });

// Normalise unknown precision

function normalizeTs(ts) {

return ts.toString().length >= 13 ? ts : ts * 1000;

}

`

The Year 2038 Problem

A 32-bit signed integer overflows at 2147483647` — 2038-01-19 03:14:07 UTC. The fix: 64-bit integer storage, which handles dates ~292 billion years into the future. Most modern systems already do this.

Quick Conversion Tool

Use our Timestamp Converter — real-time current timestamp display, plus two-way conversion between seconds/milliseconds and local time.