Free Time Duration Calculator
Updated September 2026
Calculate the duration between a start and end date/time, down to the second, with results in hours, minutes, seconds, and decimal hours. Free online.
Time calculations — deadlines, scheduling across time zones, date arithmetic — are surprisingly error-prone when done manually. The Time Duration Calculator makes them instant and accurate.
Calculate the duration between a start and end date/time, down to the second, with results in hours, minutes, seconds, and decimal hours. Free online. Results are immediate — no waiting, no loading screens, no account required.
Who uses the Time Duration Calculator?
- Calculating exact worked hours from a single clock-in and clock-out time pair for payroll.
- Figuring out how long an event, flight, or task took given its start and end timestamps.
- Runners and cyclists computing elapsed time between a start and finish timestamp.
Common uses and search terms
The Time Duration Calculator is frequently used for: time duration, time difference, hours between. Whether you need a quick result or are working through a longer project, the tool handles all common variations without any configuration.
Why use Allio Tools's Time Duration Calculator?
Everything runs locally in your browser. No data is sent to a server, logged, or stored anywhere. The tool is completely free with no usage limits, no premium tiers, and no account required. Available in 11 languages and optimised for all screen sizes, the Time Duration Calculator works on desktop, tablet, and mobile with no app download needed.
See also:Time Zone Converter · Online Stopwatch · Date Calculator
How the Time Duration Calculator works
Enter a start date and time.
Enter an end date and time — if the end is before the start, the result is shown as negative with an "end before start" note rather than being auto-corrected.
Click Calculate Duration.
View the result in hours, minutes, seconds, and decimal hours, plus a combined total line.
Tips & tricks
- There's no "spans midnight" toggle or AM/PM format switch — enter full start and end dates (not just times) and the browser's native time input handles the rest.
- If your end date/time is earlier than your start, the result displays as negative with an "(end before start)" note instead of silently producing a wrong answer.
- There's no mode to add several separate durations into a running total, and no mode to compute an end time from a start time plus a duration — this tool is strictly start/end → duration.
- The decimal hours figure is what you want for payroll or billing calculations where hours get multiplied by a rate.
Frequently Asked Questions
How do I calculate time duration that crosses midnight?
Set the end date to the following calendar day (not just a later time on the same day) and enter the end time — since both fields include full dates, the tool naturally computes the correct duration across midnight without needing a separate toggle.
Is there a "spans midnight" checkbox?
No — there's no such toggle. Because you enter a full date and time for both start and end, crossing midnight is handled automatically by using different calendar dates, not by a special option.
Can I add multiple time durations together, like a running total from several entries?
No — this tool only computes the duration between one start and one end date/time pair per calculation. There's no running total or multi-entry addition mode.
What is decimal hours and when is it used?
Decimal hours express time as a decimal number: 1h 30m = 1.5 hours; 2h 45m = 2.75 hours. Decimal hours are used in time tracking, billing, and payroll systems where hours are multiplied by hourly rates.
Can I calculate an end time from a start time plus a duration (e.g. "3h 20m after 9:00")?
No — the tool only works in one direction: given a start and an end, it computes the duration between them. There's no "start + duration = end" mode.
Is my data safe when using the Time Duration Calculator?
Completely safe. The Time Duration Calculator processes everything locally in your browser. No input data, results, or usage information is ever transmitted to or stored on any server.
Does the Time Duration Calculator automatically account for daylight saving time?
Yes. The Time Duration Calculator uses your browser's built-in time zone data, which includes daylight saving time rules for all supported time zones, keeping results accurate year-round.
How does the Time Duration Calculator handle daylight saving time and leap years?
The Time Duration Calculator uses your browser's built-in Intl and Date APIs, which automatically account for daylight saving time transitions, leap years, and regional time zone rules. You do not need to make any manual adjustments for these calendar events.
Works with ChatGPT, Claude, Cursor, GitHub Copilot, VS Code, Poe and more — 106+ tools, zero data collection.