Add, subtract, and convert time in hours, minutes, and seconds. Includes time difference between two clock times and a unit converter.
Add or Subtract Time
Starting time
Second value
Quick presets
04:15:00
Duration in hours, minutes, seconds
Total seconds
15300
Total minutes
255
Decimal hours
4.25 h
Days
0.1771
Time Difference Between Two Clock Times
Start time
End time
08:15:00
Elapsed duration between start and end
Total seconds
29700
Total minutes
495
Decimal hours
8.25 h
Days
0.3438
Time Unit Conversion
01:30:00
Equivalent in HH:MM:SS format
Milliseconds
5 400 000
Seconds
5400
Minutes
90
Hours
1.5
Days
0.0625
Weeks
0.0089
Conversion reference table
From
Seconds
Minutes
Hours
Days
1 second
1
0.0167
0.000278
0.0000116
1 minute
60
1
0.0167
0.000694
1 hour
3 600
60
1
0.0417
1 day
86 400
1 440
24
1
1 week
604 800
10 080
168
7
Frequently Asked Questions
How does the Add / Subtract tab handle 24-hour overflow?
The calculator treats values as durations, not clock times. Adding 20:00:00 + 8:00:00 returns 28:00:00 as the total duration, along with the equivalent in days. If you need clock-time arithmetic (e.g., 20:00 plus 8 hours = 04:00 the next day), use the Time Difference tab in "Next day" mode or subtract 24:00:00 from the result.
What happens if I subtract a larger value from a smaller one?
The result becomes negative and is shown with a minus sign (for example, −01:15:00). Total seconds, minutes, and hours also show the negative value. This is useful when you want to know how much earlier one time is compared to another.
Why does the Time Difference tab have a "Next day" option?
Work shifts, flights, and overnight events often cross midnight. If the start is 22:00 and the end is 06:00 the following morning, selecting "Next day" produces a positive 8:00:00 duration. Without it, the calculator would return a negative result because end < start on the same day.
How precise are the decimal hours and days values?
Decimal hours are rounded to 4 decimal places (for example, 1.5833 h for 1 h 35 min). Days are rounded to 6 decimal places so that short durations still produce a non-zero reading. The internal calculation uses integer seconds, so rounding happens only at the display stage.
Can I enter more than 59 minutes or seconds?
Yes. You can type 90 into the minutes field and the calculator normalizes the result automatically — 0h 90m 0s becomes 01:30:00. Hours have no upper limit, so you can enter durations of hundreds of hours for long projects or cumulative tracking.
What is the difference between this and a date calculator?
A date calculator operates on calendar dates (days, months, years) and answers questions like "what date is 90 days from today". This Time Calculator operates on durations (hours, minutes, seconds) and answers questions like "how long between 09:15 and 17:30" or "what is 2h 30m plus 1h 45m". They complement each other for different planning tasks.
Results are calculated locally in your browser. No data is sent anywhere.
The Time Calculator performs arithmetic on time durations expressed in hours, minutes, and seconds. Three modes are available. Add / Subtract combines two HMS values and reports the result with 24-hour overflow handled as a total duration, so 20:00:00 + 8:00:00 returns 28:00:00. Time Difference measures the elapsed duration between a start and an end clock time, with a Next day option for overnight shifts that cross midnight (for example 22:00 to 06:00 gives 8:00:00). Unit Conversion turns a raw value in milliseconds, seconds, minutes, hours, days, or weeks into every other unit at once, plus an HH:MM:SS equivalent. Every result is also shown in total seconds, total minutes, decimal hours, and decimal days for quick use in payroll, cooking, workouts, and project tracking.