Duration Calculator Free Online
Convert any duration between milliseconds, seconds, minutes, hours, days, and weeks. Or calculate the exact difference between two datetimes. Runs entirely in your browser.
Pro — ISO 8601 duration format, duration arithmetic, API access
API access · Priority queue · Team workspace
How It Works
Enter a Value
Type any duration value and choose its unit from the dropdown — milliseconds, seconds, minutes, hours, days, or weeks. Or switch to the Date Difference tab and pick two datetimes.
Instant Conversion
All 6 units update in real time as you type. A human-readable breakdown (e.g. "2 days, 3 hours, 15 minutes") is also shown so the duration is immediately understandable at a glance.
Copy Any Unit
Click Copy next to any unit to put its value on your clipboard. Copy seconds for an API parameter, hours for a report, or the human-readable string for a UI label.
Duration Calculator Features
6-unit conversion, date difference, and human-readable output in one tool
6 Time Units
Milliseconds, seconds, minutes, hours, days, and weeks — all converted simultaneously from a single input. No need to run multiple conversions.
Human-Readable Output
A natural breakdown like "2 days, 3 hours, 15 minutes, 30 seconds" is generated automatically, making the duration immediately understandable for any audience.
Date Difference
Switch to the Date Difference tab, pick a start and end datetime, and get the absolute elapsed time in every unit. Accounts for timezone offsets and DST.
Real-Time Output
Results in unit-converter mode update as you type — no submit button needed. This makes it fast to experiment with different input values and units.
One-Click Copy
Each unit result has its own Copy button so you can grab exactly the value you need — seconds for a server config, hours for a spreadsheet, or ms for a benchmark.
100% Offline
All calculations run locally in your browser. No data is ever sent to a server, making it safe for sensitive time data from internal systems or audit logs.
Free vs Pro
| Feature | Free | Pro |
|---|---|---|
| Unit conversion (6 units) | ||
| Date difference calculator | ||
| Human-readable output | ||
| Duration arithmetic (add/subtract) | — | |
| ISO 8601 duration format (P1Y2M…) | — | |
| REST API access | — |
Frequently Asked Questions
Milliseconds, seconds, minutes, hours, days, and weeks — all shown simultaneously from a single input value. A human-readable breakdown is also generated automatically.
The human-readable field breaks the total duration into its largest meaningful components, e.g. "2 days, 3 hours, 15 minutes, 30 seconds" instead of a single large number in one unit.
Select a start and end datetime using the date/time pickers, then click Calculate. The tool computes the absolute difference and shows it in all 6 units plus the human-readable breakdown.
Yes. The Date Difference calculation uses JavaScript's Date object, which handles leap years, DST transitions, and timezone offsets automatically. The result reflects the actual elapsed wall-clock time.
ISO 8601 durations look like P1Y2M3DT4H5M6S (1 year, 2 months, 3 days, 4 hours, 5 minutes, 6 seconds). This compact, machine-readable format is used in many APIs and data formats. It is supported in the Pro plan.
No. All calculations run locally in your browser using JavaScript. Nothing is transmitted to any server, making it safe for private or sensitive time data.