⏱️ Development
Unix Timestamp Converter
Turn a Unix timestamp into a readable date, or a date into seconds and milliseconds since 1970. Choose a direction, enter the value, then press Convert.
About the Unix Timestamp Converter
Unix time counts the seconds since 00:00:00 UTC on 1 January 1970, excluding leap seconds. It is timezone-free: the same timestamp is 12:00 in London and 07:00 in New York, but it denotes the same instant. This converter shows both the UTC and local renderings so the offset is visible.
Milliseconds are the same count multiplied by 1,000. JavaScript's Date.now() returns milliseconds, while most Unix command-line tools and databases store seconds. If a timestamp looks about a thousand times too large, it is almost certainly in milliseconds.
How the calculation works
- Unix seconds = milliseconds ÷ 1,000.
- Date → timestamp: Date.UTC(year, month − 1, day, h, m, s) ÷ 1,000.
- Leap seconds are not counted in Unix time.
- 1 day = 86,400 Unix seconds.
Reference values
| Timestamp | UTC date | What it marks |
|---|---|---|
| 0 | 1970-01-01 00:00:00 | Unix epoch |
| 1,000,000,000 | 2001-09-09 01:46:40 | A famous round number |
| 1,700,000,000 | 2023-11-14 22:13:20 | Late 2023 |
| 1,767,225,600 | 2026-01-01 00:00:00 | Start of 2026 |
| 2,000,000,000 | 2033-05-18 03:33:20 | 2033 |
Worked example: one instant, three time zones
The timestamp 1,700,000,000 is 14 November 2023 at 22:13:20 UTC. In New York (UTC−5) it is 17:13; in Tokyo (UTC+9) it is 07:13 the next day. A millisecond timestamp such as 1,700,000,000,000 is the same instant; divide by 1,000 before formatting.
That is the practical value of Unix time: it stores an instant without a time zone. The local rendering is a display choice, not part of the number. When a log entry looks about a thousand times too large, it is almost certainly in milliseconds, a common JavaScript convention.
Time zones, daylight saving and local time
Unix time is always UTC, so the number itself never shifts when a country changes its clocks. The local rendering does shift, and twice a year a local time can be ambiguous: when clocks go back, 01:30 occurs twice, and when they go forward, 01:30 does not occur at all. Converting a stored local time back to a timestamp therefore needs the time-zone rules, not just an offset.
Use the IANA time-zone database, usually through your language's standard library, rather than a fixed offset. Offsets change when governments alter daylight-saving policy, sometimes at short notice, and a hard-coded −05:00 will silently misplace events in New York by an hour for half the year.
Frequently asked questions
Sources and standards
Unix time counts seconds from 1 January 1970 UTC and ignores leap seconds. The conversion follows RFC 3339 for the textual form and IANA zone data for local offsets, so a timestamp near a daylight-saving change is handled correctly.