Time Calculator
Add and subtract hours, minutes and seconds, or find the duration between two times.
All calculations happen locally in your browser — nothing is uploaded, stored or tracked.
Pick a mode
Add duration, duration between times, or total a list.
Enter the times
Use the time pickers or type HH:MM.
Read the result
Formatted as hours, minutes and seconds.
What Is a Time Calculator?
Time arithmetic is base-60, which makes it easy to get wrong by hand: 90 minutes is an hour and a half, not 1.5 decimal hours. This calculator handles the carrying between seconds, minutes and hours automatically.
Three modes cover the common cases: adding or subtracting a duration to a start time (useful for scheduling), finding the duration between two clock times (handling overnight spans correctly), and summing a list of durations (for timesheets and running logs).
How Time Arithmetic Works
All times are converted to a total number of seconds, the operation is performed in seconds, then the result is converted back to hours, minutes and seconds with correct carrying. Durations between clock times that cross midnight are handled by assuming the second time is on the following day if it is earlier.
Your data never leaves your device.
Every calculation on this site runs in your browser using vanilla JavaScript. Nothing is uploaded, stored or tracked.
- 100% local, client-side calculations
- No data stored on any server
- No tracking, no analytics, no ads scripts
- Works offline once loaded
Frequently Asked Questions
How do I add hours and minutes?
Enter the start time and the duration — the calculator carries minutes over 60 into hours automatically.
How is the duration between two times calculated?
Both times are converted to seconds and subtracted. If the end time is earlier than the start, it is treated as the next day.
Why is 1.5 hours not 1 hour 50 minutes?
Because time is base-60: 0.5 hours is 30 minutes. The calculator works in true hours:minutes:seconds, never decimal hours.
Can I total up multiple durations?
Yes — switch to the total mode and add each duration as a row. It is handy for timesheets.
Does it handle overnight shifts?
Yes. A duration between 22:00 and 06:00 correctly returns 8 hours.