Can the total be negative?

Yes. If the durations you subtract are larger than the durations you add, the total is shown with a minus sign so you can see the shortfall.

How accurate is the calculation?

It is exact integer arithmetic. Each duration is converted to whole seconds, summed with its sign, and re-expanded to hours, minutes and seconds with no rounding loss.

Are my durations sent anywhere?

No. The tool is privacy-first — every value you type stays in your browser and is never uploaded to a server.

What is decimal hours and why is it shown?

Decimal hours expresses the total as a single number of hours — for example 2 hours 30 minutes is 2.5 hours. It is the form most billing and payroll systems expect.

How many durations can I add?

As many as you like. Use Add duration to insert new rows, and remove any row with its delete button; the total updates instantly.

Can minutes or seconds exceed 60?

Yes. You can enter 90 minutes or 120 seconds and the tool normalises the total correctly — 90 minutes becomes 1 hour 30 minutes in the result.

What is this useful for?

Totalling billable time, summing audio or video clip lengths, adding training-session times, and netting project hours against a budget.

Time Duration Adder — Gera Tools

Time duration adder

This tool adds and subtracts a list of hours-minutes-seconds durations and gives the combined total in three forms. It is handy for billing time, editing audio and video, logging training, and netting project hours against a budget.

How it works

Each row has an add/subtract toggle and hours, minutes, seconds fields. The tool converts every row to whole seconds (h × 3600 + m × 60 + s), negating it if the row is set to subtract, then sums all rows. The total seconds are re-expanded into HH:MM:SS, and also shown as a plain second count and as decimal hours:

total seconds = Σ (±(h × 3600 + m × 60 + s))
HH:MM:SS      = expand(total seconds)
decimal hours = total seconds ÷ 3600

All of it is exact integer arithmetic, so there is no rounding loss. Inputs are not capped at 60, so 90 minutes normalises correctly.

Example

Add 1:30:00 and 0:45:00, then subtract 0:15:00: the seconds are 5400 + 2700 − 900 = 7200. That expands to 02:00:00, which is 7,200 seconds and 2 decimal hours. If you subtract more than you add, the result carries a minus sign to show the shortfall.

It is privacy-first: every duration you enter stays in your browser and is never sent anywhere.