Calendar-aware
“One month” follows the calendar and clamps to the last valid day when needed. January 31 plus one month lands on the end of February.
How long?
What date?
Compare two moments, or move a date forward and back by calendar units. Leap years, short months, and your local time zone are handled on purpose.
Your dates stay here. Everything runs in this browser. No dates, schedules, or results are uploaded or saved.
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Choose what you want to calculate
Only your selected mode is remembered. The dates themselves are not.
Device time zone: . Daylight-saving changes can make an elapsed “day” contain 23 or 25 hours.
Calendar difference
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Exact elapsed days0
Uses 24-hour units.
Exact elapsed hours0
Includes daylight-saving changes.
Two honest answers
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02
03
Calendar time and elapsed time.
Exact totals
Elapsed days and hours come from the actual timestamps, so daylight-saving transitions are visible instead of quietly rounded away.
Local and forgetful
The math runs locally. Dates are not sent anywhere and disappear when you close or refresh the page.
Date math, explained.
Why can one calendar day be 23 or 25 hours?
When daylight-saving time begins or ends, the clock can jump forward or repeat an hour. The calendar difference can still say one day while the exact elapsed total reflects the clock change.
What happens to January 31 plus one month?
The result moves to the last valid day of February. This avoids JavaScript's surprising rollover into March and matches how people usually mean calendar-month math.
Does this handle time zones in other cities?
It uses the time zone configured on your device. It does not convert between two named world time zones; both inputs are interpreted in the same local zone.