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Adding and subtracting hours, minutes, and seconds

September 24, 2026

Time does not add like normal decimals because there are 60 minutes in an hour and 60 seconds in a minute. The simplest method is to convert everything to seconds, do the math, and convert back. The Time Calculator does exactly that.

Method

  1. Convert each time to seconds: hours × 3,600 + minutes × 60 + seconds.
  2. Add or subtract the two totals.
  3. Convert back: divide by 3,600 for hours, then divide the remainder by 60 for minutes. What is left is seconds.

Worked examples

  • 2:45:30 plus 1:30:45 is 9,930 + 5,445 = 15,375 seconds, which is 4:16:15.
  • 1:15 minus 2:40 is -1:25:00. The minus sign means the second time was longer.
  • 20 hours plus 9 hours 5 minutes is 29:05:00, which is 1 day 5 hours 5 minutes.

To find the time between two clock times, such as 9:00 AM and 5:30 PM, use the Hours Calculator instead.