Unix timestamp converter

What a Unix timestamp is

A Unix timestamp counts the seconds elapsed since 1970-01-01 00:00:00 UTC, a moment called the epoch. It carries no timezone: the same instant has the same timestamp everywhere on earth, which is exactly why systems store time this way and convert to a local calendar only when displaying it.

Seconds or milliseconds?

This is the single most common source of a “my date is in 1970” bug. Different platforms picked different units:

The quick check is length. A seconds value for any date near now has 10 digits; a milliseconds value has 13. Feeding a milliseconds value to something expecting seconds lands you somewhere around the year 57000; the reverse lands you in January 1970.

Getting the current timestamp

date +%s                      # shell, seconds

Date.now()                    // milliseconds
Math.floor(Date.now() / 1000) // seconds

import time; int(time.time())

SELECT EXTRACT(EPOCH FROM NOW());  -- PostgreSQL

The year 2038 problem

Systems that store the timestamp in a signed 32-bit integer overflow at 2147483647, which is 2038-01-19 03:14:07 UTC. The counter wraps to a large negative number and the date jumps to 1901. Modern 64-bit platforms are unaffected, but the issue still surfaces in embedded firmware, older file formats, and database columns declared as 32-bit.

A note on timezones

The timestamp itself is absolute, but the calendar date you convert it to is not. This converter shows both UTC and your browser’s local time, and they will differ whenever your offset is not zero, sometimes by a full calendar day. When you compare a converted date against another system’s, check you are comparing the same zone before assuming there is a bug.

Your data stays here

The conversion is arithmetic performed in your browser. Nothing you type is sent anywhere.