Three simple steps
How to use the Time Calculator
- 01
Enter the starting time in 24-hour format.
- 02
Choose add or subtract and enter a duration.
- 03
Read the resulting time and day offset.
Everyday time tool
Time Calculator
Add or subtract a duration from a clock time and see whether the result falls on the same, previous or following day.
Instant calculation Runs in your browser
Resulting time
12:15Same day
Duration applied2 h 45 min
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Worked example
Add 2 hours 45 minutes to 09:30
Calculation09:30 + 02:45
Result12:15 on the same day
The method
How it works
Convert to minutes
The starting time and duration are converted to minutes so addition or subtraction stays exact.
Wrap at midnight
Results are normalised to a 24-hour clock, with a separate offset showing how many day boundaries were crossed.
Durations over 24 hours
Large hour values are supported and may move the result several days forward or backward.
Helpful answers
Frequently asked questions
Can I subtract past midnight?
Yes. The clock result wraps correctly and the day label shows a negative offset.
Does it use 12-hour or 24-hour time?
Inputs and results use an unambiguous 24-hour clock.
Does it account for time zones?
No. This is clock arithmetic and does not apply time zones or daylight-saving rules.