Time Duration Calculator

Calculate elapsed date/time differences, overnight shifts or a date/time after adding or subtracting a duration. Deduct breaks and copy the result.

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How to Use the Time Duration Calculator

Choose date/time difference, time-only shift, add duration or subtract duration. Enter the relevant start/end values. Elapsed modes allow a break deduction; add/subtract modes use duration days, hours and minutes. Choose 24-hour or 12-hour result display. All values use UTC or the same explicitly entered fixed UTC offset, with no automatic daylight-saving adjustment.

Formula and Explanation

Elapsed minutes = (end timestamp − start timestamp) / 60,000
Time-only: add 24 hours when end time is earlier than start
Net minutes = elapsed minutes − break minutes
Decimal hours = net minutes / 60
Calendar-day difference = difference between civil date midnights
New timestamp = start timestamp ± duration minutes × 60,000

Date/time values are interpreted in a fixed-offset civil time system, never the browser’s local timezone. UTC is the default; an offset such as +420 minutes labels both endpoints UTC+07:00. No regional daylight-saving rule is inferred. Elapsed duration measures hours/minutes, while calendar-day difference counts midnight boundaries before break deduction. Equal time-only endpoints mean zero hours, not a 24-hour shift.

Fixed UTC offsets do not model daylight-saving transitions or named regional timezones. For a shift crossing an offset change, convert both endpoints to UTC outside this tool before entering them. It does not model leap seconds, payroll rules or business-day calendars. Date inputs support years 0001–9999 and minute precision; fractional duration or break minutes may produce seconds in results. A break cannot exceed elapsed time.

Worked Example

An overnight shift from 22:00 to 06:00 spans 480 minutes. Deduct a 30-minute break to get 450 minutes, 7.5 decimal hours. From 2024-02-28 12:00 to 2024-03-01 12:00 in UTC is 48 hours because 2024 has February 29. Adding 90 minutes to 2025-01-31 23:30 gives 2025-02-01 01:00.

Frequently Asked Questions

Will daylight-saving changes be handled automatically?

No. Both endpoints use UTC or one fixed offset. To measure an interval crossing a daylight-saving change, first convert its actual endpoints to UTC. The tool does not silently use the browser’s timezone.

How does an overnight time-only shift work?

If the end clock time is earlier than the start, the end is treated as the next day. Equal clock times mean zero duration. Use date/time mode for intervals of 24 hours or longer.

Why can calendar days differ from elapsed days?

Calendar-day difference counts midnight boundaries between the dates. A two-hour interval from 23:00 to 01:00 crosses one calendar day but is only two elapsed hours. Break deduction changes elapsed totals, not those date boundaries.

Can breaks or subtraction make the result invalid?

A break larger than the elapsed interval is rejected. Subtracting a duration from a date is supported, but its resulting date must stay within years 0001–9999. Add/subtract mode does not also deduct breaks.