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Time Calculator

Time arithmetic converts hours, minutes, and seconds into total seconds, performs the calculation, then converts back: Total Seconds = H x 3600 + M x 60 + S. This calculator provides three operations in one page. Add time to a starting duration, subtract time from a duration, or find the difference between two times. Results display in HH:MM:SS format with the total seconds shown.

Quick Answer

2 hours 30 minutes plus 1 hour 45 minutes equals 4 hours 15 minutes (15,300 total seconds). The difference between 9:00 and 17:30 is 8 hours 30 minutes.

Add Time

Subtract Time

Time Between

Common Examples

Input Result
2h 30m + 1h 45m 4 hours, 15 minutes, 0 seconds
5h 0m 0s - 1h 30m 0s 3 hours, 30 minutes, 0 seconds
Between 9:00:00 and 17:30:00 8 hours, 30 minutes, 0 seconds
0h 45m 30s + 0h 20m 45s 1 hour, 6 minutes, 15 seconds

How It Works

The Formula

All time arithmetic works by converting hours, minutes, and seconds to a single unit (total seconds), performing the operation, then converting back:

To Total Seconds: Total = H x 3600 + M x 60 + S

From Total Seconds: H = floor(Total / 3600), M = floor((Total mod 3600) / 60), S = Total mod 60

Addition: Result = Start Total Seconds + Added Total Seconds

Subtraction: Result = Start Total Seconds - Subtracted Total Seconds

Difference: Result = Time2 Total Seconds - Time1 Total Seconds

Where:

  • H = hours
  • M = minutes (0-59 in output)
  • S = seconds (0-59 in output)
  • 3600 = seconds in one hour (60 x 60)

Overflow and Carry

When minutes or seconds exceed 59, they carry over to the next higher unit. For example, 1 hour + 1 hour 45 minutes + 30 minutes = 3 hours 15 minutes (75 minutes becomes 1 hour 15 minutes, added to the existing 2 hours). This is handled automatically by the total-seconds conversion.

Negative Results

Subtracting a larger time from a smaller one produces a negative result. The calculator displays this with a minus sign. For example, 1 hour minus 2 hours 30 minutes = -1 hour 30 minutes.

Common Use Cases

Time calculations are used for tracking work hours, computing exercise duration, calculating cooking or baking times, planning event schedules, and determining elapsed time for billing purposes.

Worked Example

To add 2 hours 30 minutes to 1 hour 45 minutes: Start total seconds = 2 x 3600 + 30 x 60 + 0 = 9,000. Add total seconds = 1 x 3600 + 45 x 60 + 0 = 6,300. Sum = 9,000 + 6,300 = 15,300 seconds. Convert back: H = floor(15,300 / 3600) = 4, remainder = 15,300 - 14,400 = 900. M = floor(900 / 60) = 15. S = 0. Result: 4 hours, 15 minutes, 0 seconds.

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Frequently Asked Questions

Can I enter more than 59 minutes or seconds?
Yes. The calculator accepts any numeric value for hours, minutes, and seconds. Values over 59 for minutes or seconds are automatically carried over. For example, entering 90 minutes is treated as 1 hour 30 minutes.
What happens if the subtraction result is negative?
The calculator displays a minus sign before the result. For example, subtracting 3 hours from 1 hour 30 minutes gives -1 hour 30 minutes, shown as -01:30:00.
Can I use this for clock times like 9 AM to 5 PM?
Yes. Use the Time Between section. Enter 9:00:00 as Time 1 and 17:00:00 as Time 2 (using 24-hour format). The result is 8 hours, 0 minutes, 0 seconds.
How do I calculate total work hours for the week?
Add each day's work duration using the Add section. For example, start with Monday's hours, note the result, then use that as the start time and add Tuesday's hours. Repeat for each day.
Does this calculator handle days?
The calculator works in hours, minutes, and seconds. Hours can exceed 24, so results like 26 hours 15 minutes are valid. To convert to days, divide the total hours by 24.