How it works
What it reads
A number is a Unix timestamp: seconds since 1 January 1970 UTC, or milliseconds once it has twelve digits or more. Four digits on their own are a year. A date written as 2026-10-24 09:30 (with or without seconds, with a space or a T) has no zone, so it is read as a wall-clock time in your own time zone, or in the From zone on the Time zones tab.
Anything else the browser understands, such as an ISO 8601 date with Z or an offset, or an RFC 822 date from an email or HTTP header, is read as the exact instant it names. Until you type, the field follows the clock and shows the current Unix time.
Unix seconds = (instant − 1970-01-01T00:00:00Z) ÷ 1000 ms
Adding and subtracting
Minutes and hours are added as elapsed time. Days, weeks, months and years move the date on the calendar of your time zone and keep the same time of day, so adding a day across a daylight-saving change still lands at the same hour. A month added to 31 January stops at the last day of February.
The difference between start and end is shown as whole days, hours, minutes and seconds, and as total days and hours. You can also pick an end date directly and read the gap.
Time zones
Zone names and offsets come from the browser’s own time zone database (the IANA database, through Intl), so they follow daylight saving for the date shown, not for today. A wall-clock time that a daylight-saving jump skips, such as 02:30 on the morning clocks go forward, is moved to the next real time.
