Time Calculator — Step-by-Step Solutions
The Time Calculator performs arithmetic with hours, minutes, and seconds. It supports four modes: add or subtract time durations, find the difference between two times, convert time to decimal hours, and convert decimal hours back to hours and minutes.
Enter your time values and get instant results. Perfect for timesheets, project tracking, cooking, and any situation where you need to work with time durations.
Your calculations will appear here
How to Use the Time Calculator
- Add/Subtract Time: enter Time 1 and Time 2 as hours, minutes and seconds, choose add or subtract, and read the result in HH:MM:SS along with the total seconds.
- Time Difference: enter two times to get the gap between them. The result is always positive, whichever time is earlier.
- To Decimal Hours: enter hours, minutes and seconds to convert to decimal hours, for timesheets and pay. From Decimal Hours: enter a number such as 2.75 to see it as hours, minutes and seconds.
- Hours can exceed 24, so the tool also works for total durations and not just clock times.
Formula and Theory
Time is written in a base-60 system for minutes and seconds, which is why ordinary decimal arithmetic goes wrong with it. 1 hour is 60 minutes and 1 minute is 60 seconds, so 1 hour is 3,600 seconds.
The reliable method for any time calculation is to convert everything to seconds, do the arithmetic, and convert back. The conversion to seconds is hours x 3,600 + minutes x 60 + seconds. To convert back, the hours are the whole number of 3,600s, the minutes are the whole number of 60s in the remainder, and the seconds are what is left.
Decimal hours are used in timesheets and billing because they can be multiplied by an hourly rate. To convert, divide the minutes by 60 and the seconds by 3,600 and add: 7 h 45 min is 7 + 45/60 = 7.75 hours. A common mistake is reading 7.45 hours as 7 h 45 min; it is actually 7 h 27 min.
This tool does durations. It does not know about dates, time zones or daylight saving, so a result is a length of time, not a clock reading on a particular day.
Worked Examples
Example 1: Adding two durations
Problem: Add 2:45:30 and 1:30:45.
Solution: Convert to seconds: 2:45:30 = 7,200 + 2,700 + 30 = 9,930 s. 1:30:45 = 3,600 + 1,800 + 45 = 5,445 s. Sum = 15,375 s. Convert back: 15,375 / 3,600 = 4 hours with 975 s left; 975 / 60 = 16 minutes with 15 s left.
Answer: 4:16:15
Example 2: Subtracting time
Problem: Subtract 1:50:30 from 5:15:00.
Solution: 5:15:00 = 18,900 s. 1:50:30 = 6,630 s. Difference = 12,270 s = 3 hours (10,800 s) + 1,470 s = 3 h + 24 min (1,440 s) + 30 s.
Answer: 3:24:30
Example 3: Time between two clock readings
Problem: How long is it from 9:15:00 to 17:45:30?
Solution: 9:15:00 = 33,300 s. 17:45:30 = 63,930 s. Difference = 30,630 s = 8 hours (28,800 s) + 1,830 s = 8 h + 30 min (1,800 s) + 30 s.
Answer: 8:30:30
Example 4: Hours and minutes to decimal hours
Problem: A shift lasts 7 hours 45 minutes. How many decimal hours is that? And 2 h 20 min 30 s?
Solution: 7 h 45 min = 7 + 45/60 = 7 + 0.75 = 7.75. For 2 h 20 min 30 s: 20/60 = 0.3333 and 30/3600 = 0.00833, so 2 + 0.3333 + 0.0083 = 2.3417.
Answer: 7.75 hours; 2.3417 hours
Example 5: Decimal hours to hours and minutes
Problem: Convert 2.75 hours and 8.4 hours to hours and minutes.
Solution: 2.75 hours: the 0.75 is 0.75 x 60 = 45 minutes, so 2 h 45 min. 8.4 hours: 0.4 x 60 = 24 minutes, so 8 h 24 min.
Answer: 2:45:00 and 8:24:00
Frequently Asked Questions
How do I add hours and minutes?
How do I convert minutes to decimal hours?
Why is 7.45 hours not 7 hours 45 minutes?
What happens when a subtraction goes negative?
Can I use it for durations over 24 hours?
Does it handle time zones or dates?
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