Time Calculator
Add or subtract time durations, or calculate the difference between two dates and times
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Quick summary
A time calculator adds, subtracts, and compares time durations or datetime values. All calculations work by converting to seconds (the base unit), performing arithmetic, then converting back to hours/minutes/seconds.
Reviewed by Simple Calculators TeamLast reviewed
How to use this calculator
- Enter the inputs requested by the calculator.
- Choose the units or options that match your situation and review the assumptions.
- Run or update the calculation to see the result.
- Review the result, breakdown, and formulas shown on the page.
- Check the inputs, units, dates, and limitations before saving or sharing the result.
Time Calculation Formulas
Adding Time Durations
- T₁, T₂
- Time durations in hours:minutes:seconds
Worked example
1h 45m 30s + 2h 20m 45s
- Given
- T1 = 1:45:30T2 = 2:20:45
- Calculation
- Result
- 4h 6m 15s
Time Unit Conversions
- h
- Hours
- m
- Minutes
- s
- Seconds
Worked example
Convert 90 minutes
- Given
- minutes = 90
- Calculation
- Result
- = 1 hour 30 minutes
Frequently asked questions
How do I add hours and minutes?
Convert everything to seconds, add them up, then convert back. For example, 1h 30m + 2h 45m = (5400+1800) + (9900) = 19500 seconds = 5 hours 25 minutes.
Can I calculate the difference between two specific dates?
Yes! Use "Time Between Dates" mode and enter start and end datetime values. The calculator returns the difference in days, hours, minutes, and seconds.
What happens when subtraction gives a negative result?
If the result is negative (e.g., 1h − 2h), the display shows a minus sign and the absolute value. This indicates the first duration is shorter than the second.
How many seconds are in a day?
1 day = 24 hours × 60 minutes × 60 seconds = 86,400 seconds. A week = 604,800 seconds. A year (365 days) ≈ 31,536,000 seconds.
Key terms
- Duration
- A length of time, expressed in hours, minutes, and seconds.
- Unix Timestamp
- The number of seconds since January 1, 1970 (UTC). Used internally for date calculations.
- Elapsed Time
- The amount of time that has passed between a start and end point.
- Time Arithmetic
- Adding or subtracting time values, with carrying/borrowing between seconds, minutes, and hours.
Methodology, sources & limitations
This page shows the formula, assumptions, and limitations used for this estimate. Rates, thresholds, and other time-sensitive inputs can change, so verify them against the relevant official source before relying on a result.
For our review approach and the primary sources we consult, see the methodology and source policy. If you spot an outdated figure or formula, please contact us with a correction.