Time Calculator
Add, subtract or convert hours, minutes and seconds.
TL;DR — Time Calculator: A time calculator performs arithmetic on durations expressed in hours, minutes and seconds, and converts between time units. Use it for adding billable hours, computing total runtime, scheduling and unit conversions like seconds-to-hours.
What is the Time Calculator?
A time calculator performs arithmetic on durations expressed in hours, minutes and seconds, and converts between time units. Use it for adding billable hours, computing total runtime, scheduling and unit conversions like seconds-to-hours.
How to use the Time Calculator
- Enter the first duration (hours, minutes, seconds).
- Choose add or subtract.
- Enter the second duration.
- Read the resulting duration in normalised h:mm:ss format.
Formula
Sum (s) = h₁·3600 + m₁·60 + s₁ + h₂·3600 + m₂·60 + s₂ Then normalise: hours = floor(sum ÷ 3600); minutes = floor((sum mod 3600) ÷ 60); seconds = sum mod 60
For subtraction, the result is the absolute difference between the two durations.
Worked example
2h 45m 30s + 1h 30m 45s = 4h 16m 15s. (10,530 s + 5,445 s = 15,975 s → 4·3600 + 16·60 + 15.)
Frequently asked questions
How do I convert hours to minutes?
Multiply by 60. 2.5 hours = 150 minutes.
How many seconds are in a day?
86,400 seconds — 24 × 60 × 60.
Can the calculator handle durations longer than 24 hours?
Yes. The result is shown as total hours (e.g. 28h 30m), not in days.
How do I add decimal hours?
Enter as hours, minutes and seconds. 1.25 hours = 1h 15m 0s.
Can it calculate elapsed time between two clock times?
For elapsed time on the same day, subtract the earlier from the later. Cal44 also has a Date Difference Calculator for cross-day spans.