JS Date & Timezone Guide

Get the Current Unix Timestamp in JavaScript

To get the current Unix timestamp in seconds, use Math.floor(Date.now() / 1000); Date.now() alone gives milliseconds. Part of Unix Timestamps & Epoch Conversion.

Why this scenario is tricky

JavaScript counts the epoch in milliseconds, but Unix time, database epoch functions, and JWT exp/iat claims count whole seconds. Emit the milliseconds where a millisecond value is expected and the seconds where seconds are — mixing them puts a token's expiry a thousand-fold too far in the future.

Milliseconds vs whole secondsDate.now() is ms; JWT exp is secondsMilliseconds vs whole secondsDate.now() as 'exp'expiry ~year 56 000Math.floor(Date.now()/1000)correct secondsDivide by 1000 and floor whenever a seconds-based system is on the other end.

Minimal working solution

const ms = Date.now();                 // 1710513000123 (milliseconds)
const seconds = Math.floor(ms / 1000); // 1710513000 (whole seconds)

Now to secondsRead ms, floor to whole secondsNow to secondsDate.now()ms/ 1000floorseconds

Full production version

// Name the unit so callers cannot mix them up.
export const nowMs = () => Date.now();
export const nowSeconds = () => Math.floor(Date.now() / 1000);
export const nowInstant = () => nowMs(); // pass ms to new Date()

Unit-named helpersExpose ms and seconds explicitlyUnit-named helpersDate.now()nowMs()nowSeconds()named unit

Verification snippet

Get the Current Unix Timestamp in JavaScript — assertionsKey cases assert correctlyAssertions that prove the edge casenowSeconds() digits10nowMs() digits13ratio~1000xJWT exp usesseconds

Common pitfalls

Current Unix Timestamp pitfallsCommon mistakes and their fixesWrongRightsend Date.now() as exp1000x too largefloor(Date.now()/1000)secondsparse seconds with new Date()lands in 1970name variables by unitno mixups

Frequently Asked Questions

How do I get the current Unix timestamp in seconds?

Use Math.floor(Date.now() / 1000). Date.now() returns milliseconds since the epoch, and Unix time is measured in whole seconds, so you divide by 1000 and floor to drop the millisecond remainder.

Why does my JWT expire immediately or never?

You likely passed Date.now() (milliseconds) where the exp claim expects seconds, or vice versa. JWT exp and iat are Unix seconds, so use Math.floor(Date.now() / 1000) when signing and compare against seconds when validating.