Time Calculator
Add or subtract hours, minutes, and seconds. Convert between time units. Calculate time differences and durations.
Enter time values and click Calculate.
How Does the Formula Work?
The time calculator adds or subtracts two time durations expressed in hours, minutes, and seconds. It writes the result back as hours, minutes, and seconds and converts it to total seconds, minutes, hours, and days; solving the tedious arithmetic of carrying over 60 seconds to a minute and 60 minutes to an hour.
1. Convert each time to total seconds:
Total = hours × 3600 + minutes × 60 + seconds
2. Add or subtract the totals
3. Convert back to hours, minutes, seconds:
Hours = total ÷ 3600 (integer part)
Minutes = (remainder) ÷ 60 (integer part)
Seconds = final remainder
Unit Conversions:
Total Minutes = total seconds ÷ 60
Total Hours = total seconds ÷ 3600
Total Days = total seconds ÷ 86,400
Example: 2 hours 45 minutes 30 seconds + 1 hour 30 minutes 45 seconds
= 9,930 s + 5,445 s = 15,375 s
= 4 hours 16 minutes 15 seconds
How Carrying Works
Time arithmetic uses base-60 for seconds and minutes, not base-10 like regular math. When 45 minutes plus 30 minutes equals 75 minutes, the result carries over: 1 hour and 15 minutes. Similarly, 50 seconds plus 25 seconds equals 75 seconds, which becomes 1 minute and 15 seconds. The calculator handles all carrying automatically by converting to total seconds, performing the operation, then converting back.
Negative Results
Subtracting a larger time from a smaller one produces a negative result. For example, 1 hour minus 1 hour 30 minutes equals negative 30 minutes. The calculator puts a minus sign in front of the duration, the clock, and the totals. Negative time differences are useful for calculating time deficits, schedule overruns, or how much time you are behind.
Common Uses
Timesheet calculations; adding up hours worked across multiple shifts or days. Cooking; combining preparation and cooking times for a meal. Exercise; totaling workout durations across different activities. Travel; adding flight time plus layover plus ground transport. Project management; estimating total time from task durations. Video editing; calculating total runtime from individual clips. The calculator handles any duration from seconds to hundreds of hours.
Overflow Input
You can enter values above 59 in the minutes or seconds fields. Entering 90 minutes is treated as 1 hour 30 minutes. Entering 3,661 seconds is treated as 1 hour 1 minute 1 second. This is convenient when you have a total in one unit and want to see the hours, minutes, and seconds without converting manually.
Durations, Not Clock Times
The calculator adds and subtracts lengths of time; it does not read times of day or convert between time zones. A clock reading can still become a duration. To find how long a shift from 08:30 to 17:15 on the same day lasts, subtract 8 hours 30 minutes from 17 hours 15 minutes: the result is 8 hours 45 minutes. Keep in mind that 90 minutes is 1.5 hours; as a duration it is written 1 hour 30 minutes, which is the form the fields take.
Units and Limits
Each field takes a whole number from 0 to 1,000,000,000; a decimal such as 1.5 hours gets a message asking for 1 hour and 30 minutes instead. The conversions follow Table 8 of NIST SP 330, which lists the minute, the hour, and the day as units used alongside the SI: a minute is 60 seconds, an hour is 3,600 seconds, and a day is 86,400 seconds. Total minutes and total hours are rounded to two decimals, total days to four.
Tips & Recommendations
Toggle between + and − to add or subtract time durations. Subtraction can produce negative results when needed.
See your result in words, as a digital clock (HH:MM:SS), and as total seconds, total minutes, total hours, and total days.
Enter 90 minutes or 3,661 seconds; the calculator normalizes automatically. No need to pre-convert.
See the full expression (A ± B = Result) at the bottom. Copy it for timesheets or documentation.
Frequently Asked Questions
How does the time calculator work?
Enter two durations in hours, minutes, and seconds, then choose Add or Subtract. The calculator turns both into seconds, does the arithmetic, and shows the answer in words, as a digital clock (HH:MM:SS), and as total seconds, minutes, hours, and days.
Can I enter more than 59 minutes or seconds?
Yes. Each field takes any whole number up to 1,000,000,000 and the result is normalized: 90 minutes reads as 1 hour 30 minutes, and 3,661 seconds as 1 hour 1 minute 1 second.
Can I enter 1.5 hours?
The fields take whole numbers. For 1.5 hours, enter 1 hour and 30 minutes, because half an hour is 30 minutes. A decimal is not cut short in silence: the calculator shows a message that says why.
What happens with negative results?
When you subtract a longer duration from a shorter one, the result is negative. The calculator puts a minus sign in front of the duration, the clock, and the totals.
Can I calculate more than 24 hours?
Yes. Hours do not roll over into days in the main result, so 30 hours stays 30 hours; the Days box shows the same total in 24-hour days.
What units are shown in the result?
Six formats: the duration in words, a digital clock (HH:MM:SS), and the totals in seconds, minutes, hours, and days. A minute is 60 seconds, an hour 3,600 seconds, and a day 86,400 seconds (NIST SP 330, Table 8).
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