From a calendar value to an instant
Choose UTC or a named IANA time zone before converting. The input uses an unambiguous year-month-day control, so values such as 03/04/26 cannot silently change between regional date conventions. The selected zone determines the instant; changing only the output unit does not.
Seconds or milliseconds?
Seconds are common in Unix utilities and many backend systems. Milliseconds are the native unit for JavaScript Date. Microseconds and nanoseconds are used by some databases and event pipelines; choosing a finer unit adds zeros when the source input has only millisecond precision.
Daylight-saving caveat
Named-zone wall times can be missing or repeated during daylight-saving transitions. The converter rejects a nonexistent time during the spring-forward gap. If the clock repeats a local time in autumn, it shows both UTC offsets and asks you to choose the intended instant.
How to use this tool
Enter a calendar date and time, select the zone in which that clock reading was observed, then choose the output unit and press Convert. The source zone interprets the date; it is not merely a label applied to a result.
Worked input and output
| Input or setting | Expected result |
|---|---|
2023-11-14 22:13:20 · UTC · s | 1700000000 |
2023-11-15 06:13:20 · Asia/Shanghai · ms | 1700000000000 |
2023-11-14 22:13:20.123 · UTC · ms | 1700000000123 |
Checks before using the result
During a daylight-saving overlap, select the earlier or later offset explicitly. A skipped wall time is rejected. Whole-second output rounds down if the source has a fraction; choose milliseconds or a finer unit to retain supported input precision. Use the DST examples to distinguish a missing time from an invalid calendar date.