# Time Duration Calculator

> Add, subtract and average durations written as 1h 30m, 90:00 or 1:30:00.

A duration calculator adds, subtracts or averages spans of time written in any common form — 1h 30m, 1:30:00, 90m or a bare number of minutes. The result is shown as HH:MM:SS, in words, as decimal hours for timesheets, and as an ISO 8601 duration.

**URL:** https://convertto.tech/t/duration-calculator
**Category:** Date & Time Tools (https://convertto.tech/c/date-time-tools)
**Privacy:** Runs entirely in the browser; no upload
**Cost:** Free, no sign-up
**Last updated:** 2026-08-01

## Key facts

- **Privacy:** Runs entirely in your browser — nothing is uploaded
- **Cost:** Free, unlimited, no sign-up

## How to use

1. Enter or paste your durations.
2. Choose the calculate.
3. Choose the show as.
4. The result appears immediately — copy or download it.

## FAQ

### Why do timesheets use decimal hours?

Because payroll multiplies hours by a rate, and 7 hours 30 minutes cannot be multiplied directly. As 7.5 it can. That is why converting between the two is the most common timesheet operation there is.

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