How do I calculate the time between two times?

Convert both to minutes after midnight by multiplying the hour by 60 and adding the minute, then subtract. For 9:00 to 17:30 that is 1,050 minus 540, giving 510 minutes or 8 hours 30 minutes.

What happens when the end time is earlier than the start time?

The duration crosses midnight, so add a full day of 1,440 minutes to the result. A start of 22:00 and an end of 6:00 is 8 hours overnight rather than a negative number, and this calculator flags that it has made this assumption.

How do I convert decimal hours to hours and minutes?

Multiply the decimal hours by 60 and the result is the total minutes. Divide that by 60 for the hours and take the remainder for the minutes. So 8.5 decimal hours is 510 minutes, which is 8 hours 30 minutes.

Is 1.30 one hour and thirty minutes?

Not when read as a decimal. In clock notation 1:30 means one hour and thirty minutes, but written as the number 1.30 it means one point three hours, which is 1 hour and 18 minutes. This ambiguity is why decimal hours should always be written with a decimal point and clock times with a colon.

How do I add time to a clock time?

Convert to minutes after midnight, add your minutes, then divide by 60 and take the remainder for minutes. Adding 90 minutes to 09:00 gives 630 minutes, which is 10 hours 30 minutes, so 10:30.

What is the maximum duration two clock times can express?

Just under 24 hours, specifically 1,439 minutes between 00:00 and 23:59. Any longer duration needs days recorded separately, because a single pair of clock readings cannot span more than one day.

How do I calculate hours worked across a midnight shift?

Enter the shift start and shift end. If the end is earlier than the start the calculator adds the full day automatically and reports 8 hours for a 22:00 to 06:00 shift, rather than the minus 16 hours a raw subtraction would give.

Does this calculator handle seconds?

It accepts hours and minutes, and reports the total in seconds for convenience. If your source data includes seconds, convert them into the minutes field as a decimal first, which this calculator accepts.

What is the percentage of a day figure?

It is your duration expressed as a percentage of a full 24 hour day, which is 1,440 minutes. A 12 hour shift is 50 percent of the day, and this can be useful for capacity and utilisation calculations.

Why does my timesheet need decimal hours?

Payroll and invoicing systems usually store time as a decimal so arithmetic on hours works directly. Converting 8 hours 30 minutes to 8.5 avoids the classic error of entering 8.30, which would be billed as 8 hours and 18 minutes.

How to Use the Time Duration Calculator

Enter two clock times to get the duration between them in six different formats, or switch to the second mode to add or subtract time from a single clock time.

Step-by-Step Instructions

1 Enter the start time as an hour between 0 and 23 and a minute between 0 and 59.
2 Enter the end time the same way. Use 24 hour values, so 18:30 means six thirty in the evening.
3 Read the duration in words, minutes, hours and minutes, decimal hours, seconds and as a percentage of the day.
4 If the end is earlier than the start, the calculator has assumed you are measuring across midnight and tells you so.
5 For the other direction, tick Add or subtract time and enter a number of minutes, using a negative value to go backwards.

Understanding the Inputs

Start time

The starting clock time as an hour and a minute. Hours run 0 to 23 and minutes 0 to 59 in 24 hour format.

How to find it: Shift rosters, meeting times, journey departures, timers and recipe preparation times. Anything expressed as a point on the 24 hour clock.

Why it matters: Every duration calculation needs a starting point, and using 24 hour form removes the ambiguity of a bare number like 9, which could mean morning or evening.

Type: text · Default: 09:00

End time

The finishing clock time in the same 24 hour format. An end earlier than the start means the span crosses midnight.

How to find it: The end of a shift, the arrival time of a journey, or a deadline. If you are counting elapsed days rather than measuring a span, add the days separately.

Why it matters: The comparison against the start time is what determines whether midnight wrapping is needed, and getting it wrong turns a nine hour night shift into a negative number.

Type: text · Default: 17:30

Tips & Best Practices

✓ Enter 24 hour times so there is no doubt about morning and evening.
✓ Read the hours and minutes form aloud to check it, since that catches transcription errors fastest.
✓ Use decimal hours for billing and keep the colon form for schedules, and never mix them.
✓ Tick the add or subtract mode rather than doing the arithmetic by hand when times wrap midnight.

Try the Time Duration Calculator

by CalculatorPro Tools · Updated 10-12-2026