Time Duration Calculator β add, subtract & time difference
Add or subtract durations in HH:MM:SS, and find the difference between two clock times. Get a normalized result plus total minutes and seconds.
π Runs entirely in your browser. Your input and output are never sent to a server or stored β fully private.
Add or subtract durations
Enter durations as HH:MM:SS (seconds on the right; hours may exceed 24). Click any value to copy.
Difference between two times
If the end time is earlier than the start, it is treated as the next day.
About this tool
This calculator works with spans of time in hours, minutes and seconds. Add several durations together, subtract one from another, or find the gap between two clock times β and when an end time falls past midnight it wraps over correctly into the next day. It is handy for timesheets, cooking, workouts, music and video editing, or working out shift lengths. Every calculation happens in your browser, with nothing sent anywhere.
Frequently asked questions
How does it handle times that cross midnight?
When the end time is earlier on the clock than the start time β say a shift from 22:00 to 06:00 β the tool assumes it runs into the next day and adds the wrap-around, giving 8 hours rather than a negative result. This makes it reliable for night shifts and any session that spans midnight.
What is the difference between a duration and a clock time?
A clock time is a point in the day, such as 14:30, while a duration is a length of time, such as 1 hour 45 minutes. This tool does both: add or subtract durations to get a new total length, or subtract one clock time from another to find the duration between them. Minutes and seconds carry over automatically, so 90 minutes is shown as 1 hour 30 minutes.
Is my data sent anywhere?
No. Every calculation runs locally in your browser, so the clock times and durations you enter are never uploaded to or stored on a server. Because nothing leaves your device, the tool also keeps working once the page has loaded even if you lose your internet connection.