Time Duration Calculator
Use this free Time Duration Calculator to find the hours and minutes between two times, add or subtract time, or total up a timesheet's worked hours.
Find the duration between a start time and an end time. Check the box if the end time is the next day (like an overnight shift).
Add or subtract a duration from a starting time.
Enter durations in H:MM format, separated by commas, like a timesheet (e.g. 8:30, 7:45, 6:15).
How to Use the Time Duration Calculator
Pick a mode
Choose "Time Between Two Times" for a simple duration, "Add/Subtract Time" to project a new time, or "Add Multiple Durations" for a timesheet-style total.
Enter your times
Use the time picker for single times, or type comma-separated H:MM durations for the timesheet mode.
Click Calculate
Get your result instantly in hours and minutes, plus a decimal hours figure for payroll or billing use.
How This Time Duration Calculator Works
A time duration calculator handles a type of math most people get wrong without realizing it: time isn't base 10. Sixty minutes make an hour, not a hundred, which means normal subtraction and addition rules quietly break unless you borrow and carry in units of 60 instead of 10.
Finding the Duration Between Two Times
This mode converts both times into total minutes since midnight, subtracts the earlier from the later, then converts the result back into hours and minutes. This sidesteps the base-60 borrowing problem entirely.
Example: From 9:15 AM to 2:40 PM. Converting to minutes: 9:15 is 555 minutes, 2:40 PM is 880 minutes. Difference: 880 − 555 = 325 minutes, which converts back to 5 hours 25 minutes.
Handling Overnight Shifts
When a shift or event ends after midnight, the end time is technically "earlier" on the clock than the start time, even though it comes later chronologically. This time duration calculator handles that with an overnight checkbox, which adds a full 24 hours (1,440 minutes) to the calculation so the duration comes out correct instead of negative.
Example: A shift from 10:00 PM to 6:00 AM. Without adjusting for the overnight crossing, this would incorrectly calculate as a negative duration. With the adjustment, it correctly returns 8 hours.
Adding or Subtracting Time
This mode takes a starting time and a duration (hours and minutes), then adds or subtracts that duration to project a new time. It also flags whether the result crosses into the next day or the previous day, which matters for scheduling across midnight.
Totaling a Timesheet With a Time Duration Calculator
The "Add Multiple Durations" mode is built for timesheets, adding up several shift lengths (like 8:30, 7:45, 6:15) into one total. Each entry is converted to minutes, summed together, and converted back to hours and minutes, along with a decimal hours figure since payroll systems typically expect decimal format (like 7.5 hours instead of 7 hours 30 minutes) rather than H:MM.
Why Time Math in Base 60 Trips People Up
Standard timekeeping divides an hour into 60 minutes and a minute into 60 seconds, a system with roots in ancient Babylonian mathematics, as documented by resources like Encyclopedia Britannica's explanation of the sexagesimal system. Because everyday arithmetic is taught in base 10, people naturally try to subtract times the same way they'd subtract regular numbers, which produces wrong answers whenever borrowing is needed. This time duration calculator avoids that entirely by converting everything to a single unit (minutes) before doing any math, then converting back at the end.
Why Use Our Time Duration Calculator
Instant Results
Get your answer the moment you click Calculate, no waiting or reloading.
3 Calculation Modes
Time difference, add/subtract, and timesheet totals, all in one place.
100% Private
Everything runs in your browser. Your times are never stored or sent anywhere.
Works on Any Device
Fully responsive design, so it's just as easy to use on mobile as on desktop.
Overnight-Safe
Correctly handles shifts and durations that cross midnight.
Completely Free
No sign-up and no limits. Use it as often as you need, at no cost.
Frequently Asked Questions
Use the "Time Between Two Times" mode of this time duration calculator. Enter a start and end time, and it converts both to minutes to find the exact difference.
Check the "End time is the next day" box, and the calculator adds a full 24 hours to the duration so overnight shifts calculate correctly instead of returning a negative number.
Enter each duration as H:MM (hours:minutes), separated by commas, like 8:30, 7:45, 6:15. The calculator adds them all up and gives both an H:MM total and a decimal hours total.
Payroll and billing systems typically expect decimal hours (like 7.5) rather than hours and minutes (like 7 hours 30 minutes), so both formats are shown for convenience.
Yes, use the "Add/Subtract Time" mode and select subtract from the dropdown to calculate a time that many hours and minutes before your starting time.
No. All calculations happen locally in your browser, and nothing you enter is stored or transmitted.
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