What a Unix timestamp is
A Unix timestamp counts seconds since 1970-01-01 00:00:00 UTC (the "epoch"), ignoring leap seconds. It's timezone-less by design: the same instant is the same number everywhere on Earth, which is why databases, logs, and APIs love it. Milliseconds variants (13 digits instead of 10) are common in JavaScript and Java — the auto mode here tells them apart by length.
Milestones
| Timestamp | Moment |
|---|---|
| 0 | 1970-01-01 00:00:00 UTC — the epoch |
| 1,000,000,000 | 2001-09-09 — the billennium |
| 1,234,567,890 | 2009-02-13 |
| 1,500,000,000 | 2017-07-14 |
| 2,000,000,000 | 2033-05-18 |
| 2,147,483,647 | 2038-01-19 — signed 32-bit rollover ("Y2038") |
Frequently asked questions
- Does a timestamp have a timezone?
- No — it names an instant, not a wall-clock reading. Timezones only enter when you format it for humans, which is why this page shows UTC and your local time side by side.
- Seconds or milliseconds?
- Rule of thumb: 10 digits is seconds (until the year 2286), 13 digits is milliseconds. Auto mode uses that split; force the unit if you're working with unusual ranges.
- What is the year-2038 problem?
- Systems storing timestamps as signed 32-bit integers overflow at 2,147,483,647 — 2038-01-19. Modern systems use 64 bits, good for about 292 billion years.
- Can timestamps be negative?
- Yes — they count backward before 1970. −86,400 is 1969-12-31. This converter handles them fine.
- What about leap seconds?
- Unix time pretends they don't exist: days are always exactly 86,400 "seconds". For calendar math that's a feature; for sub-second astronomy, look up TAI.