What Is a Unix Timestamp? — Complete Explanation with Examples

Published August 2026 · 5 min read

The Definition

A Unix timestamp counts seconds since January 1, 1970, 00:00:00 UTC (the "epoch"). No timezones, no calendars, no leap-year logic — just one number that means the same instant everywhere on Earth.

Seconds vs Milliseconds

The most common bug in timestamp handling:

1754520000      → seconds (10 digits)  → Aug 6, 2025
1754520000000   → milliseconds (13 digits) → same instant, JS-style

JavaScript's Date.now() returns milliseconds; most server APIs return seconds. Mixing them gives dates 55,000 years in the future.

The Year 2038 Problem

32-bit signed integers max out at 2,147,483,647 = January 19, 2038, 03:14:07 UTC. Systems still storing timestamps as 32-bit ints will overflow and wrap to 1901. Modern systems use 64-bit — safe for 292 billion years.

Converting in Every Language

// JavaScript
new Date(1754520000000)
// Python
datetime.fromtimestamp(1754520000, tz=timezone.utc)
// Bash
date -d @1754520000

Try It Live

Our Timestamp Converter auto-detects seconds vs milliseconds and shows ISO, UTC, local, and relative formats — plus reverse conversion.

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