How it works
Every value is turned into seconds, added or subtracted, then turned back into days, hours, minutes and seconds. You can type more than 59 minutes or seconds (for example 90 minutes) and it carries over correctly.
For a clock time, the hours and minutes are added to the start time. If the result goes past midnight, it tells you it's the next day.
Total seconds = days × 86,400 + hours × 3,600 + minutes × 60 + seconds
Worked example
2 h 45 m + 1 h 30 m 30 s = 4 h 15 m 30 s (4.2583 hours). 8:30 AM + 10 h 45 m = 7:15 PM the same day. 10:00 PM + 5 h = 3:00 AM the next day.
Frequently asked questions
How do I add hours and minutes?
Add the minutes first. If they come to 60 or more, take 60 off and add 1 hour. 45 min + 30 min = 75 min = 1 h 15 min.
How do I subtract time?
Subtract the seconds, then minutes, then hours, borrowing 60 when needed. The calculator does the borrowing for you, and shows a minus sign if the second time is longer.
What time will it be in 8 hours?
Use the clock-time box: enter the current time and 8 hours. It tells you the time and whether it's the next day.
How many minutes are in 2.5 hours?
150 minutes. Multiply hours by 60.