Time arithmetic
Subtract time calculator
Subtract a duration from a 24-hour clock time and show any previous-day rollover.
How to use this calculator
Enter Starting hour (0–23), Starting minute (0–59), Hours to subtract and Minutes to subtract. Subtract a duration from a 24-hour clock time and show any previous-day rollover. The answer updates when you change an input.
Understanding the result
The result is ordinary clock arithmetic without a calendar date, timezone or daylight-saving adjustment. Previous-day rollover is stated explicitly.
Common questions
What assumptions does this result use?
Inputs are whole non-negative duration values; the starting time uses a 24-hour clock.
Are intermediate values rounded?
No. The calculation retains JavaScript number precision internally and formats only the displayed result unless the stated method requires a discrete whole value.