Unix timestamps, explained — and converted
A unix timestamp is a single number: the count of seconds elapsed since 00:00:00 UTC on January 1, 1970 — the epoch. No months, no timezones, no formatting ambiguity, which is exactly why APIs, databases, JWT tokens and log pipelines store time this way. The tradeoff is readability: 1750000000 tells a machine everything and a human nothing.
Converting by hand means dividing by 86,400 and counting leap years — nobody does that twice. The subtle parts are the unit (seconds or milliseconds, off by a factor of a thousand), and the timezone: a timestamp is always UTC, and only its display is local. This converter handles both directions, detects the unit automatically, and shows the same instant as ISO 8601, UTC, your local time and a relative phrase like "3 days ago".
Open the free Unix Timestamp Converter — no signup, runs entirely in your browser.
How to use it
- Paste an epoch value into the Unix to Date card — auto mode treats values of 1e12 and above as milliseconds, or force seconds/milliseconds yourself.
- Read the same instant four ways: ISO 8601, UTC, your local timezone, and a live-updating relative reading.
- Or go the other way: type an ISO date (zone-less strings are read as UTC) or use the picker, and copy the epoch seconds or milliseconds.
Why this one
- Automatic seconds-vs-milliseconds detection with explicit override for edge cases.
- Zone-less dates interpreted as UTC — no silent browser-timezone surprises.
- A live-ticking now strip with the current epoch in seconds, milliseconds and ISO 8601, one click to copy.
- Handles fractional seconds, pre-1970 negative timestamps, and dates across the full representable range.
Frequently asked questions
How do I know if my timestamp is in seconds or milliseconds?
Count the digits: a current timestamp in seconds has 10 digits, in milliseconds 13. The auto mode applies the same rule — absolute values of 1e12 and above are treated as milliseconds. For pre-2001 dates in milliseconds, pick the milliseconds unit explicitly since those values fall below the threshold.
What is the year 2038 problem?
Legacy systems store unix time as a signed 32-bit integer, which overflows at 2,147,483,647 — 03:14:07 UTC on January 19, 2038 — and wraps around to 1901. Any system still on 32-bit time_t needs migrating to 64-bit before then. Modern 64-bit timestamps are safe for roughly 292 billion years.
Do unix timestamps depend on timezones?
No — a timestamp names an absolute instant and is always UTC-based. Timezones only appear when you display it: the same value renders differently in Amsterdam and Tokyo. That is why this tool treats dates entered without an offset as UTC instead of guessing your local zone.
Why does unix time start in 1970?
The epoch is an arbitrary convention from early Unix development at Bell Labs — a recent, round date that kept the counters small. It stuck, and now everything from C libraries to JavaScript's Date measures time from that same midnight.
Can a unix timestamp be negative?
Yes. Negative values simply count seconds before the 1970 epoch: -1 is 23:59:59 UTC on December 31, 1969. They are fully valid, and this converter handles them in both directions.