Time arithmetic
Add time calculator
Add a duration to a 24-hour clock time and show any day rollover.
How to use this calculator
Enter Starting hour (0–23), Starting minute (0–59), Hours to add and Minutes to add. Add a duration to a 24-hour clock time and show any day rollover. The answer updates when you change an input.
Understanding the result
Clock arithmetic is performed as a duration without attaching a date or timezone. Day rollover is reported separately so the resulting clock time remains clear.
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.