Add Time Calculator
Adding a duration to a start time sounds trivial until the result crosses midnight or you need to subtract instead. This calculator takes a start time and an amount of hours and minutes to add, then returns the resulting clock time on the 24-hour clock along with how many whole days the result rolled forward or back. Enter negative hours or minutes to subtract, which is useful for working backwards from a deadline. It is built for scheduling tasks: finding an end time from a start and a length, timing cooking steps, or planning arrivals after a journey.
Add time formula
start minutes = hour * 60 + minute
added minutes = hours to add * 60 + minutes to add
total = start minutes + added minutes
day change = floor(total / 1440)
result clock = total mod 1440 (wrapped to 0 to 1439)
Everything is done in minutes. The day change counts whole 1,440-minute days crossed, positive for forward and negative for backward, and the result is wrapped to a valid time of day.
Add time notes
- Results are shown on the 24-hour clock (00:00 to 23:59).
- Use negative values to subtract time and work backwards.
- A day change of plus one means the result is on the next day.
- A day change of minus one means the result is on the previous day.
- The calculation works to the minute.
Add time: frequently asked questions
How do I add hours and minutes to a time?
Convert the start time and the amount to add into minutes, add them, then convert back to hours and minutes. For example, 14:30 plus 2 hours 45 minutes is 870 minutes plus 165 minutes, which is 1,035 minutes, or 17:15.
Can I subtract time as well?
Yes. Enter negative values for the hours or minutes to add to subtract instead. For example, adding minus 3 hours to 02:00 wraps back to 23:00 on the previous day, which the calculator reports as a day change of minus one.
What does the day change output mean?
Adding time can push the result past midnight into the next day or back into the previous day. The day change shows how many whole days the result moved: plus one means the next day, minus one means the day before, and zero means the same day.
Does it use a 24-hour clock?
The result is shown on the 24-hour clock, where hours run 00 to 23, so 5 in the afternoon appears as 17:00. This avoids any ambiguity between morning and afternoon that a 12-hour clock with AM and PM can introduce.
What is this useful for?
It is handy for scheduling: working out an end time from a start time and a duration, finding when a timer or cooking step finishes, planning arrival times after a journey, or adding a meeting length to a start time across a midnight boundary.
Official sources
- International Organization for Standardization: ISO 8601 date and time format.
- NIST Time and Frequency Division: Time and Frequency.
Reviewed by the CalculatorHub team, edited by James Graham, 17 June 2026. See our methodology.