How to use it
Add and subtract
- Type each duration as hours and minutes (
1:45), with seconds if needed (0:50:30), or as decimal hours (1.5). - Choose + or − in front of each row. Add a duration adds a row, × removes one.
- Read the result in h:mm, in decimal hours and in minutes. Hours are not cut at 24: 26 hours stay 26:00, with a note in days.
Time between two times
- Enter the start and end time on a 24-hour clock or with am/pm, as your device shows it.
- If the end is earlier than the start, it is the next day, as on a night shift. Equal times give zero.
How it calculates
Every duration is turned into seconds: hours × 3,600 + minutes × 60 + seconds. The signed values are added, and the sum is written back as hours, minutes and seconds. Decimal hours are the seconds divided by 3,600.
For two clock times, the start is subtracted from the end; when the end is earlier, 24 hours are added.
Worked examples
- 1:45 + 2:30: 45 + 30 = 75 minutes = 1:15, plus 3 hours = 4:15, which is 4.25 hours or 255 minutes.
- 8:00 − 0:45 = 7:15, a working day minus a lunch break.
- 0:50:30 + 0:20:45: 30 + 45 seconds = 1:15, 50 + 20 + 1 minutes = 71 = 1:11, so 1:11:15.
- 10:30 pm to 6:15 am: 1:30 to midnight + 6:15 = 7:45, or 7.75 hours.
Common mistakes
- Reading 1.30 as 1:30. In decimal hours 1.30 is 1 hour 18 minutes; 1:30 is 1.5 hours. Use a colon for hours and minutes.
- Adding times as decimals. 1.45 + 2.30 = 3.75 is not 4:15. Let the calculator carry the minutes.
- To measure time live, use the online stopwatch; to count calendar days, the days between dates calculator.