Time Duration Calculator
Find out how much time sits between a start and an end, whether that is two clock times in a day, an overnight span, or two separate date-times.
Type times in 12h (9:30 pm) or 24h (21:30). An end that lands before the start is read as crossing midnight.
Your duration will appear here
Enter a start and end time to see the time between them, including spans that cross midnight.
Which time tool should you use?
- Want to add or subtract lengths of time instead of measuring a gap? Use the Time Calculator.
- Working out hours worked with a break deducted and decimal hours? Use the Hours Calculator.
Quick Answer
This calculator measures the difference between two points in time. Give it a start and an end and it returns the length in hours and minutes, handling spans that cross midnight, with an option for two full date-times when the gap runs across days.
How It Works: Formula & Variables
Duration = End − Start (if End < Start, add 24:00)
- Convert to 24h
- Add 12 to any PM time before subtracting.
- Borrow minutes
- If the minutes go negative, take 60 from the hours column.
- Across midnight
- When the end falls on the next day, add a full 24 hours.
Worked Examples
Example 1: Within one day
From 9:34 to 11:03. Hours give 11 − 9 = 2. The minutes 03 − 34 go negative, so borrow an hour: 63 − 34 = 29, and the hours drop to 1. The duration is 1 hour 29 minutes.
Example 2: Across midnight
From 8:00 PM to 5:00 AM. The end is earlier than the start, so it lands on the next day: 05:00 + 24:00 = 29:00, and 29:00 − 20:00 = 9 hours.
Key Concepts
Midnight is the tricky part: When a span runs overnight, the raw subtraction would go negative. Adding 24 hours puts it right, which is exactly what the tool does when the end reads earlier than the start.
12-hour clocks need care: 12 AM is midnight and 12 PM is noon. Getting those two backwards throws the whole span off by twelve hours.
A duration is not the same as hours worked: This tool gives the raw gap. It does not take out a lunch break — that is what the Hours Calculator adds.
Common Mistakes
Ignoring the midnight crossing: Subtracting straight through gives a negative, when the real answer wraps into the next day.
Converting AM and PM wrong: 12 AM is midnight and 12 PM is noon, which is easy to flip.
Treating the gap as worked hours: A duration does not subtract breaks — reach for the Hours Calculator when you need that.
Frequently Asked Questions
Enter a start time and an end time and the calculator returns the length between them in hours and minutes, along with the equivalent in decimal hours.
When the end time is earlier than the start, the tool reads it as landing on the next day and adds 24 hours. So 8:00 PM to 5:00 AM comes out as 9 hours rather than a negative number.
For a clock difference the result is an absolute length, so putting the later time first does not change the answer.
Yes. The "Two date-times" tab takes a full start and end date and time and returns the gap in days, hours, minutes, and seconds.
Both work. You can type 9:30 pm or 21:30, and the calculator converts anything with PM by adding 12 hours before it does the math.
This tool measures the gap between two points in time. The Time Calculator adds and subtracts lengths of time, such as 2 hours plus 3 hours.
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