Time Calculator
What this time calculator does
This tool covers four related time calculations in one place: adding a duration to a clock time, subtracting a duration from a clock time, finding the duration between two clock times, and normalizing a raw duration (days/hours/minutes) into its total minutes, hours, and days. Switch between them using the tabs above — each mode keeps its own inputs, so switching back and forth doesn't lose what you typed.
How to use it
For add/subtract, enter a starting clock time and how many hours and minutes to add or subtract — the result shows the new time, and notes if it lands on a different day. For time between, enter a start and end clock time; if the end time is earlier than the start, it's treated as crossing into the next day rather than producing a negative result. For duration, enter days/hours/minutes directly to see the equivalent total in minutes, hours, and days.
Adding time
On the "Add time" tab, 2:35 PM plus 1 hour 45 minutes lands at 4:20 PM the same day.
Subtracting time
On the "Subtract time" tab, 2:35 PM minus 1 hour 45 minutes lands at 12:50 PM the same day.
Time between two times
On the "Time between" tab, the time between 9:15 AM and 5:45 PM is 8 hours 30 minutes. If the end time is earlier in the day than the start — an overnight range like 10:00 PM to 6:00 AM — it's treated as crossing into the next day rather than as an error.
Hours and minutes calculations
Time arithmetic works in base 60, not base 10 — 45 minutes plus 30 minutes is 75 minutes, which carries into 1 hour 15 minutes the same way 75 cents carries into a dollar. The calculator handles that carrying, and borrowing when subtracting, automatically, including rolling over into the next or previous calendar day when a result crosses midnight.
Common use cases
- Working out what time a task will finish if it starts now and takes a known duration
- Finding how long something lasted between a start and end clock time
- Converting a mixed days/hours/minutes duration into decimal hours or total minutes
- Double-checking overnight or cross-midnight time math by hand
Frequently asked questions
How do I add hours and minutes?
Switch to the "Add time" tab, enter a starting clock time, then enter how many hours and minutes to add — the result shows the new time and notes if it lands on a different day.
How do I subtract time?
Switch to "Subtract time" and enter a starting time plus the hours and minutes to subtract, the same way as adding.
How do I calculate the time between two clock times?
Use "Time between," enter a start and end clock time, and the calculator shows the duration between them.
Can the calculator cross midnight?
Yes — if adding or subtracting rolls past midnight, or the end time in "Time between" is earlier than the start time, it's treated as landing on the next day rather than producing a negative or incorrect result.
Does it support AM/PM?
Yes, times are entered and displayed in standard 12-hour clock format.