What is a Unix timestamp (epoch time)?

A Unix timestamp (also called epoch time) counts how many seconds - or sometimes milliseconds - have passed since 1970-01-01T00:00:00Z, the Unix epoch. APIs, databases, logs, and JWTs use these numbers constantly because they are compact, sortable, and timezone-agnostic at the storage layer.

What it looks like

A modern seconds timestamp is about 10 digits (for example 1710000000). The same instant in milliseconds is about 13 digits (1710000000000). Humans rarely read either form directly - converters turn them into ISO strings, UTC clocks, or local wall time.

Why systems store epoch time

• One number represents a single instant worldwide (always based on UTC)
• Easy to compare, sort, and compute durations
• Common in JSON APIs, SQL columns, Redis TTLs, and token claims
• Independent of how any one user's clock displays the day

Unix time vs calendar strings

ISO 8601 strings like 2026-08-06T15:30:00.000Z are readable and carry an explicit offset or Z for UTC. Epoch numbers are denser and avoid ambiguous locale formats. In practice you convert both ways while debugging: paste a number to see a date, or pick a date to get seconds and milliseconds.

UTC vs local (and DST)

The epoch value itself is UTC-based. Daylight saving and timezone offsets only change how that instant is displayed as local wall time. When you compare logs across regions, stick to UTC or ISO with an explicit offset so two people are not arguing about different clocks.

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Next reads: How to convert a Unix timestamp · Unix seconds vs milliseconds