A shift that starts at 08:15 and ends at 16:45 runs 8 hours 30 minutes. That same subtraction fails the moment a night flight crosses midnight, a timesheet spans a DST change, or a departure and arrival sit in two time zones. The number you get is only right when both times live on the same calendar day in the same place.
How to calculate elapsed time on the same day
When start and end share a date, subtract the start from the end.
- Subtract the hours: 16 − 8 = 8 hours.
- Subtract the minutes: 45 − 15 = 30 minutes.
- Result: 8 hours 30 minutes.
If the end minutes are smaller than the start minutes, borrow one hour (60 minutes). From 09:45 to 14:20: 20 − 45 does not work. Borrow 60 minutes from the hour: 14:20 becomes 13:80. Now 80 − 45 = 35 minutes. Hours: 13 − 9 = 4 hours. Result: 4 hours 35 minutes.
Book meetings and log billable blocks this way. The method breaks when the end time lands on the next calendar day.
How to calculate elapsed time across midnight
When the end time is earlier in the day than the start time, the end belongs to the next day. A night shift from 22:30 to 06:15:
- Add 24 hours to the end time: 06:15 becomes 30:15.
- Subtract the start from the adjusted end: 30:15 − 22:30.
- Borrow 60 minutes: 30:15 becomes 29:75. 75 − 30 = 45 minutes. 29 − 22 = 7 hours.
- Result: 7 hours 45 minutes.
For any span under 24 hours, that is all you need. For longer spans, add the full days in between. Tuesday 22:30 to Thursday 06:15: one full day (24 hours) plus 7 hours 45 minutes = 31 hours 45 minutes.
How to calculate elapsed time with the duration tool
Manual subtraction works for a single pair. It gets slow with multiple entries, partial days, or decimal-hour conversion.
Open the Duration Calculator. Enter a start time and an end time, including dates. The tool returns the elapsed time in hours, minutes, and seconds. It handles same-day, cross-midnight, and multi-day spans.
For payroll or billing, the same calculator converts the result to decimal hours. The conversion is always minutes ÷ 60:
- 30 minutes = 0.50 decimal hours
- 15 minutes = 0.25 decimal hours
- 45 minutes = 0.75 decimal hours
- 7 minutes = 0.1167 decimal hours (exactly 7/60)
- 13 minutes = 0.2167 decimal hours (exactly 13/60)
- 40 minutes = 0.6667 decimal hours (exactly 40/60)
How to calculate elapsed time on a flight with local times
Flight schedules show departure in the departure city's local time and arrival in the arrival city's local time. Subtracting those two numbers gives you the wall-clock difference, not the flight duration.
A flight leaves London at 14:00 BST (UTC+1 in summer) and arrives in New York at 17:00 EDT (UTC−4 in summer). London is 5 hours ahead. Direct subtraction: 17:00 − 14:00 = 3 hours. Wrong. The actual flight time is 3 hours plus the 5-hour offset = 8 hours.
The correct method: convert both times to UTC first. London 14:00 BST = 13:00 UTC. New York 17:00 EDT = 21:00 UTC. Subtract: 21:00 − 13:00 = 8 hours.
Red-eye flights add a date change. Depart Los Angeles at 22:00 PDT (UTC−7) and arrive New York at 06:00 EDT (UTC−4). Convert to UTC: Los Angeles 22:00 PDT = 05:00 UTC the next day. New York 06:00 EDT = 10:00 UTC. Elapsed time: 10:00 − 05:00 = 5 hours. The clock jumps forward 8 hours, but the air time is 5.
Enter both cities and times into the Time Zone Converter. It does the UTC conversion and returns the elapsed time.
How to calculate elapsed time for sports and events
Race timing uses elapsed time from the starting gun to the finish line. A marathon starts at 07:00 and a runner crosses at 10:43. Subtract: 3 hours 43 minutes. No date change, no zone offset.
Event planning works backwards. A conference session must end at 16:30 and lasts 90 minutes. Start time: 16:30 minus 1 hour 30 minutes = 15:00. Use the Time Subtraction Calculator to back-calculate in one step.
For multi-day events, track each session's elapsed time and sum them. Three conference days with sessions of 6 hours 15 minutes, 7 hours, and 5 hours 45 minutes total 19 hours. Sum them with the Time Addition Calculator instead of carrying minutes manually.
How to calculate elapsed time when DST changes
A DST transition breaks the 24-hour day. In spring, clocks jump forward one hour at 02:00 local time. That day has 23 hours. In autumn, clocks fall back one hour at 02:00 local time. That day has 25 hours.
A night shift from 22:00 to 06:00 on the spring-forward day: clocks go from 01:59 to 03:00, skipping 02:00 entirely. Elapsed time is 7 hours, not 8. The same shift on the fall-back day covers 9 hours because 02:00 happens twice.
Open the Duration Calculator and enter the time zone for both start and end. The tool accounts for the transition. If you skip the zone, the calculator treats every hour as a standard 60-minute hour and returns the wrong result on transition days.
Most payroll systems ignore DST for local shifts because the physical time worked matches the clock. For travel, project planning, or any calculation that spans a transition, you must specify the zone. The Time Zone Help page lists which regions observe DST and when the transitions occur.