Time Duration Adder

What this tool does

The Time Duration Adder sums a list of time durations. You add a row for each length of time — entered as hh:mm:ss or hh:mm — and the tool keeps a running total, shown three ways at once: as a clock-style hh:mm:ss figure, as a plain number of total minutes, and as decimal hours. Any row can be switched to subtract instead of add, so you can deduct breaks or corrections.

It loads with three sample durations already entered and totalled, so you can see the format and the result immediately.

When you would use it

This is a tool for anyone who has to add up scattered chunks of time, which is slower and more error-prone by hand than it looks because of the base-60 carrying. Freelancers and consultants total their billable sessions for an invoice — three hours here, forty-five minutes there — and need both the clock total and the decimal hours to apply an hourly rate.

Video editors and podcasters add up clip and segment lengths to check a final runtime against a target. Anyone filling in a timesheet sums the day’s or week’s logged blocks. Musicians total track lengths to fit an album or a set within a time limit. Athletes and coaches add interval or lap times. Project leads tally estimates across tasks. In every case the subtract mode helps too — removing a lunch break from a shift, or trimming a deleted scene from a runtime.

How to use it

1. In each row, type a duration as hh:mm:ss or hh:mm. A bare number is read as minutes.
2. Leave a row on + to add it, or switch it to − to subtract it from the total.
3. Press Add duration for another row, or use the × button to remove one. The label beside each row confirms how your entry was read.
4. The total updates instantly. Read it as hh:mm:ss, total minutes, or decimal hours, whichever your next step needs.
5. Use Copy total to put a one-line summary on your clipboard.

How it works

The tool converts each row into a number of seconds, then adds or subtracts those second counts depending on the row’s toggle. Working in seconds avoids the carrying mistakes people make adding minutes by hand — 45 minutes plus 30 minutes correctly becomes 1:15, not 0:75. The total in seconds is then formatted back into hh:mm:ss, divided by 60 for total minutes, and divided by 3600 for decimal hours. Rows that cannot be understood are skipped and flagged rather than silently breaking the total.

How to read the result

The large hh:mm:ss figure is the headline. The total-minutes card is best for systems that store time as minutes. The decimal-hours card is the one to use for billing — multiply it by a rate to get a fee. If the total is negative, because subtractions outweigh additions, it is shown with a leading minus sign in a warning colour so the result is clear.

For the gap between two clock times or dates, the date difference calculator is the right tool instead.

Privacy

Every calculation runs in your browser. The durations you enter are never uploaded, never stored, and never logged. Close the tab and the list is gone, so even sensitive billable time stays entirely on your device.