Timestamp Help & Guide

What is a Unix Timestamp?

A Unix timestamp is the number of seconds that have elapsed since January 1, 1970 (UTC)—the "Unix epoch". It's a simple way for computers to represent dates and times.

Seconds vs Milliseconds

JavaScript: Uses milliseconds (Date.now() returns ms)

Unix/Python/Go: Uses seconds

API quirks: Twitter API uses seconds, Java uses milliseconds, PHP's time() returns seconds.

Time Zones

Timestamps are timezone-independent—they always represent the same moment. The "local time" you see is just the timestamp converted to your timezone.

Issue: Off by 1000x

Symptom: Date shows year 1970 or 2038.

Cause: Mixing up seconds and milliseconds.

Fix: Divide by 1000 if converting ms to seconds, multiply if going the other way.

Issue: DST Showing Wrong Time

Cause: Using local time instead of UTC, or timezone offset issues.

Fix: Always store and transmit in UTC, convert to local only for display.

Issue: 2038 Problem

Cause: 32-bit signed integers overflow at 2,147,483,647 (January 19, 2038).

Fix: Use 64-bit integers, or switch to modern timestamp formats.

Common Timestamp Formats

• Unix seconds: 1699234567
• Unix milliseconds: 1699234567000
• ISO 8601: 2024-11-05T12:56:07Z
• RFC 2822: Mon, 05 Nov 2024 12:56:07 +0000

Best Practice: Store in UTC

Always store timestamps in UTC. It's unambiguous and makes debugging easier.

// Store this in database
const utcTimestamp = new Date().toISOString();
// "2024-11-05T12:56:07.000Z"

// Not this (ambiguous without timezone)
const localString = new Date().toLocaleString();
// "11/5/2024, 12:56:07 PM"

Quick Conversions

• JS ms to Unix seconds: Math.floor(Date.now() / 1000)
• Unix seconds to JS Date: new Date(seconds * 1000)