Time Duration Calculator
Calculate how much time passes between a start time and an end time. Get the duration in hours and minutes, decimal hours, total minutes and seconds, with support for periods that cross midnight.
Calculate Time Duration
Enter two clock times and choose how overnight periods should be handled.
09:00 to 17:30 on the same day.
How the Time Duration Calculator Works
The calculator converts both clock times into the number of minutes after midnight. It then subtracts the start value from the end value.
Duration = End time − Start time
For example, 09:00 is 540 minutes after midnight and 17:30 is 1,050 minutes after midnight:
510 minutes = 8 hours 30 minutes
When the end time is earlier than the start time and overnight mode is enabled, the calculator adds 24 hours before finding the difference.
Calculating a Duration Across Midnight
Clock-time subtraction needs special handling when a period begins late on one day and finishes after midnight on the following day.
Suppose a period starts at 23:00 and ends at 02:00. Simply subtracting 23:00 from 02:00 would produce a negative value, even though the intended elapsed time is three hours.
Midnight → 02:00 = 2 hours
Total duration = 3 hours
Keep Allow overnight duration enabled when the end time belongs to the following day. If it is disabled, an end time earlier than the start time is treated as an invalid same-day range.
Time Duration Examples
| Start | End | Duration | Total Minutes |
|---|---|---|---|
| 08:00 | 16:00 | 8 hours | 480 |
| 09:00 | 17:30 | 8 hours 30 minutes | 510 |
| 09:15 | 12:45 | 3 hours 30 minutes | 210 |
| 13:20 | 18:05 | 4 hours 45 minutes | 285 |
| 22:00 | 01:00 | 3 hours overnight | 180 |
| 23:30 | 06:15 | 6 hours 45 minutes overnight | 405 |
Hours and Minutes vs Decimal Hours
A duration can be written in several equivalent forms. For example, 8 hours 30 minutes is the same elapsed time as 8.5 decimal hours or 510 minutes.
Minutes are converted to the fractional part of an hour by dividing them by 60:
8 hours + 0.5 hour = 8.5 hours
This is important because clock notation and decimal notation are not the same. For example, 7 hours 45 minutes is 7.75 hours, not 7.45 hours.
12-Hour and 24-Hour Time
The calculator input uses your browser’s native time control, while the result can be displayed using either 24-hour notation or 12-hour AM/PM notation.
For example:
- 09:00 = 9:00 AM
- 12:00 = 12:00 PM
- 17:30 = 5:30 PM
- 23:00 = 11:00 PM
- 00:00 = 12:00 AM
Changing the display format does not change the duration. It only changes how the start and end clock times are presented in the result.
When a Time Duration Calculator Is Useful
A clock-time duration calculator is useful whenever you know a start time and end time but want the elapsed period without manually subtracting hours and minutes.
- Checking the length of a work or study session
- Measuring a meeting, appointment or event window
- Calculating travel time from scheduled departure and arrival times
- Checking overnight time periods
- Planning exercise or training sessions
- Comparing available time slots during a day
- Converting an hours-and-minutes duration into decimal hours
For calculations involving full calendar dates rather than clock times alone, use ToolZippy’s Date Difference Calculator or Days Between Dates Calculator.
Important Limitations
This calculator measures elapsed clock time from the values entered. It does not automatically subtract meal breaks, rest periods or other interruptions.
It also does not apply payroll rules, overtime rules, rounding policies or employment regulations. If you are calculating paid working hours, those rules may need to be applied separately.
Because this tool uses clock times without a date or timezone, it also does not model daylight-saving clock changes. For a period affected by a timezone or daylight-saving transition, the actual elapsed time may differ from simple clock subtraction.
Browser-Based Calculation
The duration calculation on this page is designed to run in your browser with JavaScript. The start and end times are converted into minutes and the difference is calculated directly on the page.
The tool does not require an account. For important employment, transport, legal or other records, compare the calculated duration with the relevant official schedule, timesheet or source record.
Time Duration Calculator FAQs
How do I calculate the duration between two times?
Enter the start time and end time, then select Calculate Duration. The tool subtracts the start from the end and shows the elapsed hours, minutes, decimal hours, total minutes and seconds.
Can the calculator handle times that cross midnight?
Yes. Keep the overnight option enabled. If the end time is earlier than the start time, the calculator treats the end as occurring on the following day.
How long is 9:00 AM to 5:30 PM?
The elapsed duration is 8 hours 30 minutes, which is 8.5 decimal hours or 510 total minutes.
How long is 11:00 PM to 2:00 AM?
When 2:00 AM is on the following day, the duration is 3 hours.
What happens if the start and end times are identical?
You can choose whether identical times represent zero elapsed time or a full 24-hour period.
What are decimal hours?
Decimal hours express minutes as a fraction of an hour. For example, 30 minutes equals 0.5 hour, so 8 hours 30 minutes equals 8.5 hours.
Is 7 hours 45 minutes equal to 7.45 hours?
No. Forty-five minutes is 45 divided by 60, or 0.75 hour. Therefore, 7 hours 45 minutes equals 7.75 decimal hours.
Does the calculator subtract breaks?
No. It calculates the full elapsed period between the entered clock times. Meal breaks, rest breaks or other deductions must be handled separately.
Does the calculator account for daylight saving time?
No. The tool uses clock times without dates or timezones, so it does not model daylight-saving or timezone transitions.
Can I display times in AM and PM?
Yes. Select the 12-hour display option to show the entered start and end times using AM and PM notation. The calculated duration itself remains the same.