Time Duration Calculator
Add, subtract and convert hours, minutes and seconds.
Reviewed by the Calculation Machine team · Updated 24 October 2026 · How we check our maths
Your values
ⓘ Live results
- Result
- 4:05:45
- Decimal hours
- 4.0958
- Total minutes
- 245.75
- Total seconds
- 14,745
Quick answer
To add or subtract time durations, convert each one to seconds (hours × 3,600 + minutes × 60 + seconds), do the arithmetic, then convert back by dividing by 3,600 and 60. For example, 1:52:40 + 0:47:35 = 2:40:15, which is 9,615 seconds or 2.6708 decimal hours.
What the Time Duration calculator does
This calculator adds or subtracts two lengths of time written as hours, minutes and seconds, and shows the answer four ways: clock-style HH:MM:SS, decimal hours, total minutes and total seconds. It is built for durations rather than times of day, so the hours are not capped at 24 — 36:15:00 is a valid entry.
Typical uses are totaling video or audio clip lengths, taking an unpaid break off a shift, comparing a race finish with a goal time, and converting a stopwatch reading into the decimal hours that payroll and invoicing systems expect. If you need the time between two clock times on a timesheet, the time card hours calculator handles start and end times directly; for gaps between calendar dates, use the date difference calculator.
When the second duration is larger than the first in subtract mode, the result is shown with a minus sign, which tells you how far short of (or ahead of) a target you are.
The formula
Total seconds = (h₁ × 3600 + m₁ × 60 + s₁) ± (h₂ × 3600 + m₂ × 60 + s₂) Hours = ⌊total ÷ 3600⌋, minutes = ⌊(total mod 3600) ÷ 60⌋, seconds = total mod 60 Decimal hours = total seconds ÷ 3600
| Symbol | Meaning | Unit |
|---|---|---|
| h, m, s | Hours, minutes and seconds of each duration | h, min, s |
| 3600 | Seconds in one hour | s/h |
| 60 | Seconds in one minute, and minutes in one hour | — |
| ⌊ ⌋ | Round down to a whole number | — |
This is ordinary sexagesimal (base-60) arithmetic, the system used for time since Babylonian astronomy and fixed by the SI definition of the second. Working in whole seconds avoids the classic mistake of "borrowing" 100 instead of 60 when subtracting minutes. The method does not handle days, time zones or daylight-saving changes — it treats every hour as exactly 3,600 seconds.
Worked examples
Total running time of two clips
A video editor joins a 1 h 52 min 40 s main feature with a 47 min 35 s extras reel.
Inputs
- First duration1:52:40 HH:MM:SS
- Second duration0:47:35 HH:MM:SS
- OperationAdd
Result
- Result2:40:15
- Decimal hours2.6708
- Total minutes160.25
- Total seconds9,615
The seconds (40 + 35 = 75) roll over into an extra minute and the minutes (52 + 47 + 1 = 100) roll over into an extra hour, giving 2:40:15. That is 160.25 minutes if your storage or upload tool asks for minutes.
Shift length minus an unpaid break
An 8 h 30 min shift with a 45-minute unpaid lunch.
Inputs
- First duration8:30:00 HH:MM:SS
- Second duration0:45:00 HH:MM:SS
- OperationSubtract
Result
- Result7:45:00
- Decimal hours7.75
- Total minutes465
- Total seconds27,900
Paid time is 7:45:00, which payroll records as 7.75 hours — not 7.45. Multiply 7.75 by the hourly rate to get the day's gross pay.
Marathon finish against a goal time
A runner finishes in 3:58:12 and wants to know how far under a 4:10:00 goal that is.
Inputs
- First duration3:58:12 HH:MM:SS
- Second duration4:10:00 HH:MM:SS
- OperationSubtract
Result
- Result−0:11:48
- Decimal hours-0.1967
- Total minutes-11.8
- Total seconds-708
The result is −0:11:48: the runner beat the goal by 11 minutes 48 seconds. A negative answer always means the first duration is the shorter one.
Minutes to decimal hours conversion table
Timesheets, invoices and payroll software usually want decimal hours, while stopwatches and media players show minutes and seconds. Divide minutes by 60 to convert. Many employers round to the nearest quarter hour (0.25); US federal rules allow rounding to the nearest 5, 6 or 15 minutes as long as it averages out fairly over time.
| Minutes | Decimal hours | Minutes | Decimal hours |
|---|---|---|---|
| 5 | 0.0833 | 35 | 0.5833 |
| 6 | 0.10 | 40 | 0.6667 |
| 10 | 0.1667 | 45 | 0.75 |
| 15 | 0.25 | 48 | 0.80 |
| 20 | 0.3333 | 50 | 0.8333 |
| 25 | 0.4167 | 55 | 0.9167 |
| 30 | 0.50 | 60 | 1.00 |
Mistakes that give the wrong total
- Treating 1:30 as 1.30 hours. Thirty minutes is half an hour, so 1:30 equals 1.5 decimal hours. Writing 1.30 under-bills by 12 minutes.
- Using a normal calculator on clock times. Typing 2.45 + 1.20 gives 3.65, which is meaningless; the correct sum of 2:45 and 1:20 is 4:05.
- Borrowing 100 instead of 60. When subtracting 0:50 from 2:10, borrow one hour as 60 minutes: 1:70 − 0:50 = 1:20.
- Dropping the hours field. Enter 45 minutes as
0:45:00. A value with only two parts, such as45:00, is read as 45 hours and 0 minutes.
Adding more than two durations
The calculator combines two durations at a time. To total a list — a week of shifts or a playlist — add the first two, copy the HH:MM:SS result into the first box, then add the next item. Alternatively, convert each item to total seconds, add those in a spreadsheet, and enter nothing but the final figure here to convert it back. For pace and split work, the running pace calculator converts time and distance together.
How to use the Time Duration Calculator
- 1Type the first duration as hours:minutes:seconds, for example `2:45:30`. Hours can go above 24.
- 2Type the second duration in the same format. Use `0:` for the hours when a value is under an hour, such as `0:45:00`.
- 3Choose Add to combine the durations or Subtract to take the second away from the first.
- 4Read the HH:MM:SS result, then use the decimal hours, total minutes or total seconds figure for payroll, billing or software inputs.
Frequently asked questions
How do I convert hours and minutes to decimal hours?
Divide the minutes by 60 and add the result to the hours. 7 hours 45 minutes is 7 + 45 ÷ 60 = 7.75 hours.
How many seconds are in an hour?
There are 3,600 seconds in an hour (60 minutes × 60 seconds) and 86,400 seconds in a 24-hour day.
Can I add durations longer than 24 hours?
Yes. The hours are not wrapped at 24, so adding 20:00:00 and 10:30:00 gives 30:30:00 rather than 6:30 the next day.
What does a negative result mean?
It means you subtracted a longer duration from a shorter one. The size of the result is the gap between them, so −0:11:48 means the first time was 11 minutes 48 seconds shorter.
How do I work out hours between two clock times?
Enter the later time as the first duration and the earlier time as the second, then subtract: 17:15:00 − 08:40:00 = 8:35:00. For shifts that cross midnight, add 24 hours to the end time first.
References
- The International System of Units (SI Brochure) – definition of the second — Bureau International des Poids et Mesures (BIPM)
- 29 CFR 785.48 – Use of time clocks (rounding of recorded hours) — US Department of Labor, Wage and Hour Division
About this calculator
- Built and reviewed by the Calculation Machine team · How we build and test calculators
- Last reviewed: October 24, 2026
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