Time Duration Calculator
This Time Duration Calculator works out how long a period lasts across dates — in days, hours, minutes and seconds.
- Spans any range — hours, days, months or years, using the real calendar.
- Leap years handled — February 2024 is 29 days, February 2025 is 28.
- Free, no signup — the maths runs in your browser, nothing is sent anywhere.
Calculation details
Need to calculate something else?
Enter a start and an end
The result updates as you type.
About the Time Duration Calculator
The Time Duration Calculator measures how much time sits between two points on the calendar. Give it a start date and time and an end date and time, and it returns the length of that period broken into days, hours and minutes — plus the same span expressed as decimal days, total hours, total minutes and total seconds.
It is the tool to reach for when a period runs past midnight or across several dates. For two clock times on a single day, the Time Difference Calculator is quicker.
How to calculate a duration
- Enter the start date and time — when the period began.
- Enter the end date and time — when it finished.
- Read the result. It updates as you type; nothing is submitted anywhere.
Duration formula
Both points are converted to a single number — milliseconds since a fixed reference — then subtracted:
days = total ÷ 86,400,000 → take the whole number
hours = remainder ÷ 3,600,000 · minutes = remainder ÷ 60,000
Because both points carry a real calendar date, month lengths and leap days are handled by the calendar itself rather than by an assumption that every month is 30 days.
Worked examples
| Start | End | Duration |
|---|---|---|
| 18 Aug 2026, 9:00 AM | 21 Aug 2026, 5:00 PM | 3d 8h 0m |
| 15 Jan 2026, 9:15 AM | 15 Jan 2026, 5:45 PM | 0d 8h 30m |
| 31 Dec 2026, 10:00 PM | 1 Jan 2027, 6:00 AM | 0d 8h 0m |
| 1 Feb 2024, 12:00 PM | 1 Mar 2024, 12:00 PM | 29d 0h 0m |
| 1 Feb 2025, 12:00 PM | 1 Mar 2025, 12:00 PM | 28d 0h 0m |
The last two rows are the same dates a year apart. February 2024 has 29 days because 2024 is a leap year, so the duration is a full day longer — the kind of thing a fixed 30-day month would get wrong.
Durations that cross months and years
A period running from 20 December to 5 January crosses a month boundary and a year boundary at once. Both are handled the same way: the calculator works from the two real dates, so no manual adjustment is needed for month lengths, year ends or leap days.
Frequently asked questions
How do I calculate the duration between two dates and times?
Enter a start date and time and an end date and time. The result appears immediately as days, hours and minutes, with decimal days, total hours and total minutes underneath.
Does it handle leap years and different month lengths?
Yes. The calculation is made from the two real calendar dates, so February’s length and any leap day are accounted for automatically.
How is this different from the Time Difference Calculator?
The Time Difference Calculator compares two clock times within a single day or overnight. This one takes full dates as well, so it can measure a period lasting days, months or years.
Can I see the total in hours or minutes only?
Yes. Alongside the days-hours-minutes breakdown, the result shows the same period as decimal days, total hours and total minutes.
What if the end is earlier than the start?
The calculator tells you the end falls before the start rather than showing a negative number, so you can correct the dates.
Is my data stored?
No. Everything runs locally in your browser. Nothing you type is sent to a server, and no account is required.