About this tool
This calculator adds or subtracts two durations, each entered as days, hours, minutes, and seconds, and automatically handles the base-60 carrying (60 seconds to a minute, 60 minutes to an hour, 24 hours to a day) that makes time math error-prone by hand. Everything runs in your browser.
How to use the Duration Calculator
- Fill in Duration 1 using its four boxes: Days, Hours, Min and Sec. A blank box counts as zero.
- Pick the Operation: Add (+) or Subtract (−).
- Fill in Duration 2 the same way.
- Read the Result, written as days, hours, minutes and seconds (for example 1d 2h 5m 0s), and the line below it with the total in seconds, minutes and hours.
Worked example
A project has 1 day 2 hours left before its deadline, and the next task will take 3 hours 30 minutes. To find the time left after that task, enter 1 day and 2 hours as Duration 1, choose Subtract (−), and enter 3 hours and 30 minutes as Duration 2. The result is 22h 30m 0s, and the totals line reads Total: 81000s · 1350.00 min · 22.50 hr. The calculator converts both durations to seconds (93,600 and 12,600), subtracts, then splits the answer back into hours and minutes.
Not the same as elapsed time between two clock times
This tool combines two durations you already have — like 2 hours 30 minutes plus 1 hour 45 minutes. If you instead need to find how much time passed between two specific clock times, like 9:00 AM and 5:30 PM, that's a different calculation — use the Time Duration Calculator for that instead.
Real-world use cases
- Payroll and timesheets: summing multiple work shifts into a total
- Video and audio editing: adding clip lengths to check a total runtime against a time slot
- Software and server logs: subtracting timestamps to find a request duration or job runtime
- Event planning: stacking segment durations to build a run-of-show schedule
Why time math breaks a normal calculator
Ordinary arithmetic runs on base 10, but time runs on base 60 for seconds and minutes (and base 24 for hours in a day) — so 45 minutes plus 30 minutes isn't 75, it's 1 hour 15 minutes. A regular calculator has no idea time works this way, which is exactly the class of error this tool eliminates by converting everything to a common unit, doing the math, and converting back with the correct carrying.
Things to watch out for
Subtracting a larger duration from a smaller one produces a negative result, shown with a minus sign — this is mathematically correct but worth double-checking that you entered the durations in the order you intended. This tool doesn't account for calendar specifics like different month lengths, since it works in pure days/hours/minutes/seconds rather than calendar dates.
Adding and subtracting durations
Durations are measured in hours, minutes and seconds, which use base 60 rather than base 10. That is why 1 hour 45 minutes plus 1 hour 30 minutes is 3 hours 15 minutes, and why reading those inputs as the decimals 1.45 + 1.30 gives the wrong answer of 2.75. To use a duration in pay or billing, convert to decimal hours by dividing minutes by 60: 45 minutes is 0.75 hours. Watch for sums above 24 hours, which are still valid durations and not clock times.
Frequently asked questions
This tool adds or subtracts two duration values you already have — like 2 hours 30 minutes plus 1 hour 45 minutes. Finding the elapsed time between two clock times, like 9:00 AM to 5:30 PM, is a different calculation — use the Time Duration Calculator for that instead.
Time uses base-60 math, not base-10 — 60 minutes make an hour, so 75 minutes automatically converts ("carries over") into 1 hour 15 minutes. This tool handles that conversion automatically so you don't have to do it by hand.
Yes, when subtracting a larger duration from a smaller one — the result is shown with a minus sign, representing a negative total duration.