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
- Enter the first duration across days, hours, minutes, and seconds.
- Choose add or subtract.
- Enter the second duration — the result updates instantly.
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.
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.