Time Duration Calculator

What is a time duration calculator?

A time duration calculator finds how much time passes between a start time and an end time. It handles the hour, minute, and second subtraction for you and shows the same duration in several useful formats.

This calculator works entirely in your browser. It does not upload the times or dates you enter.

How to use the time duration calculator

1. Enter the Start and End times.
2. Turn on Add dates when the duration spans more than one day.
3. Read the duration, decimal hours, total minutes, and total seconds.

The calculator opens with an example and updates immediately. Use Now to capture the current local time for either endpoint, Swap to exchange the endpoints, or Reset to restore the example.

Time duration example

From 9:15 AM to 5:45 PM, the duration is:

8 hours 30 minutes
08:30:00
8.5 decimal hours
510 total minutes
30,600 total seconds

How time duration is calculated

The basic formula is:

Duration = End time − Start time

Hours, minutes, and seconds are converted to total seconds before subtraction. The result is then split back into days, hours, minutes, and seconds.

Calculating time across midnight

When dates are off and the End time is earlier than the Start time, the calculator treats the End as the next day.

10:00 PM → 6:00 AM = 8 hours

Equal Start and End times produce a duration of zero, not 24 hours.

Calculating a duration with dates

Turn on Add dates for a duration that spans multiple calendar days. Both date and time values are treated as wall-clock values in the same time zone. The End date and time must not be before the Start.

The calculator does not convert time zones or adjust the result for daylight saving time changes.

Hours, minutes, and decimal hours

Clock duration and decimal hours express the same length of time in different ways. For example, 30 minutes is half an hour, so 8 hours 30 minutes equals 8.5 hours.

Total minutes and total seconds are useful when another calculation or system expects a single unit. If the input includes seconds, the total-minute result can contain a decimal.

Time duration calculator FAQ

Does the calculator handle overnight times?

Yes. With dates off, an End time earlier than the Start is treated as the following day.

Can I calculate a duration longer than 24 hours?

Yes. Turn on Add dates and choose the Start and End dates.

Does the time input use a 12-hour or 24-hour clock?

The native time control follows your browser and device settings. The calculated duration is the same in either format.

Does the calculator handle time zones or daylight saving time?

No. It compares wall-clock values in one time zone and does not apply DST adjustments or time zone conversion.

Does Now keep updating?

No. Now captures the local date and time when you select it. This calculator is not a stopwatch or live timer.

Can I deduct breaks or calculate payroll hours?

No. This tool calculates one continuous duration and does not include breaks, wages, overtime, or timesheets.