Unix Timestamps: A Complete Developer's Guide

Table of Contents

• What is a Unix Timestamp?
• The Epoch Explained
• Milliseconds vs Seconds
• Year 2038 Problem
• Language Examples

What is a Unix Timestamp?

A Unix timestamp is the number of seconds that have elapsed since January 1, 1970, 00:00:00 UTC — known as the Unix epoch.

// Current timestamp (seconds)
const now = Math.floor(Date.now() / 1000);

// Convert timestamp to Date
const date = new Date(1708560000 * 1000);
console.log(date.toISOString()); // '2024-02-22T00:00:00.000Z'

The Epoch Explained

Why 1970? When Unix was developed, its creators picked January 1, 1970 as an arbitrary but convenient starting point. Unix time counts seconds elapsed, making date arithmetic trivially simple:

const ONE_DAY = 60 * 60 * 24; // 86400 seconds
const thirtyDaysAgo = Math.floor(Date.now() / 1000) - 30 * ONE_DAY;

Milliseconds vs Seconds

Quick check: 13 digits = milliseconds, 10 digits = seconds.

Year 2038 Problem

32-bit systems store Unix timestamps as a signed 32-bit integer, which overflows at 2,147,483,647 — January 19, 2038. Modern 64-bit systems won't have this problem for ~292 billion years.

Language Examples

import time
now = int(time.time())  # seconds

now := time.Now().Unix()  // seconds

use std::time::{SystemTime, UNIX_EPOCH};
let now = SystemTime::now().duration_since(UNIX_EPOCH).unwrap().as_secs();

Use the Timestamp Converter to convert any Unix timestamp to a human-readable date.