Add or subtract hours, minutes and seconds, find the difference between two times, convert between units of time, or change decimal hours (such as 1.25) into hours, minutes and seconds and back again.
➕ Add or Subtract Time
Start Time
Time to Add/Subtract
📝 Calculation Details
⏱️ Calculate Time Difference
Start Time
End Time
💡 Tip
Perfect for calculating work hours, meeting durations, or time spent on tasks!
🔄 Convert Time Units
🔢 Decimal Time Converter
Convert between standard time format and decimal hours
📖 About Decimal Time
💼 Use Cases
- Payroll calculations
- Time tracking for billing
- Project management
- Converting timesheets to decimal format
What this time calculator does
- Add/Subtract: adds or subtracts one hh:mm:ss duration from another and shows the result, including negative results.
- Time Difference: the gap between two times, treating both as times on the same day.
- Convert Units: converts seconds, minutes, hours, days, weeks, months and years.
- Decimal Time: converts hh:mm:ss to decimal hours, which is useful for timesheets, and decimal hours back to hh:mm:ss.
How it works
Everything is converted to seconds, calculated, and converted back. Decimal hours = hours + minutes ÷ 60 + seconds ÷ 3600. In the unit converter a month is 30 days and a year is 365 days, as labelled.
Worked examples: 10:30:00 + 02:45:30 = 13:15:30. The difference between 09:15:00 and 17:30:00 is 08:15:00. 1:30:00 is 1.5 hours. 1.15 hours is 1 hour 9 minutes (01:09:00). 2 hours is 7,200 seconds.
Things to keep in mind
The Time Difference tab does not handle spans that cross midnight; work out the part before and the part after midnight separately and add them on the Add/Subtract tab. Months and years are fixed-length approximations, so use the Date Calculator when you need exact calendar months.
Frequently asked questions
How do I convert minutes to decimal hours?
Divide the minutes by 60. For example, 45 minutes is 0.75 hours.
Can I get a negative result?
Yes. Subtracting a longer duration from a shorter one shows the result with a minus sign.
Looking for more? See all our free academic and scientific calculators.