Time Calculator
Add or subtract a duration to a time, or find exactly how much time passes between two times of day.
If the end time is earlier than the start time, it's treated as happening the next day.
About the Time Calculator
Adding or subtracting durations by hand runs into the same problem every time: hours and minutes don't carry over in base 10 the way normal arithmetic does, so "2:45 PM plus 40 minutes" isn't simply adding 45 and 40. This tool handles the carrying correctly, including wrapping around midnight when a calculation crosses into the next (or previous) day.
Two distinct modes
"Add or subtract duration" answers questions like "what time will it be in 3 hours and 20 minutes?" — useful for scheduling, cooking timelines, or working out a departure time from a known arrival time. "Duration between two times" answers the reverse: given a start and end time, how much time actually elapsed — useful for logging work hours, tracking how long a task took, or checking flight/travel durations.
The midnight-crossing case
If the end time in "duration between two times" is earlier than the start time, the tool assumes it happened the next day rather than returning a negative or nonsensical result — so 10 PM to 2 AM correctly returns a 4-hour duration, not an error.
Frequently Asked Questions
What happens if I subtract more time than the start time has?
It wraps around to the previous day — for example, subtracting 2 hours from 01:00 gives 23:00, with a day offset shown.
Can I calculate duration across midnight?
Yes — in “Duration between two times,” if the end time is earlier than the start time, it's treated as happening the next day (e.g. 22:00 to 02:00 gives a 4-hour duration).