Time Calculator
Add or subtract durations in days, hours, minutes and seconds, convert h:mm:ss to decimal hours, and find the time between two clock times.
The interactive tool loads here when JavaScript runs.
About this toolWhat is the Time Calculator?
Times do not add like ordinary numbers. Sixty seconds carry into a minute and sixty minutes into an hour, so 2:45:50 plus 1:30:20 is 4:16:10, not 3:75:70. The Time Calculator handles that carrying for you in four modes that cover the questions people usually have about time.
Add or subtract durations takes any number of rows in days, hours, minutes and seconds, each with a plus or minus sign, and gives the total as h:mm:ss, days-hours-minutes-seconds, decimal hours, minutes and seconds. The converter turns h:mm:ss into decimal hours and back. Time between two times measures the gap between two clock readings, including across midnight. Add time to a clock time tells you what time it will be after a duration, and on which day.
Every result updates as you type, shows the steps it took, and can be copied or shared as a link.
- Add and subtract any number of d/h/m/s durations with carry
- h:mm:ss and decimal hours converter in both directions
- Time between two clock times with overnight handling
- Add or subtract a duration from a clock time, with day and date roll-over
- 12-hour or 24-hour display
- Step-by-step working, copy and share link
How to use the Time Calculator
- Pick a mode: add or subtract durations, convert h:mm:ss and decimal hours, time between two times, or add time to a clock time.
- For durations, fill in days, hours, minutes and seconds on each row, press the sign button to switch a row to subtraction, and add rows as needed.
- For conversions, type a time such as 7:45:00 or switch direction and type decimal hours such as 7.75.
- For clock times, enter the start and end, or a start time, an optional date and a duration to add or subtract.
- Read the highlighted result and the step-by-step working, then copy or share it.
Worked examples
Adding and subtracting durations
Input
+ 2 h 45 m 50 s, + 1 h 30 m 20 s, - 16 m 10 s
Output
4:00:00, which is 4 decimal hours or 240 minutes
9,950 s + 5,420 s - 970 s = 14,400 s. Dividing by 3,600 gives exactly 4 hours.
Decimal hours to h:mm:ss
Input
7.75 hours
Output
7:45:00 (465 minutes)
0.75 of an hour is 0.75 x 60 = 45 minutes. Read the other way, 7:45 is 7.75 hours, not 7.45.
Time between two times across midnight
Input
Start 22:15, end 06:40
Output
8h 25m (8.4167 hours), crosses midnight
The end is earlier than the start, so a day is added: 06:40 + 24:00 - 22:15 = 8:25.
Adding a duration to a clock time
Input
Start 09:30, add 10 h 45 m
Output
20:15 the same day
Adding 50 hours to 08:00 instead would give 10:00 two days later, and the result line says so.
Background and insight
The calculator turns everything into seconds before doing arithmetic: days x 86,400 + hours x 3,600 + minutes x 60 + seconds. It sums the signed rows and splits the result back into units. Because the units are only split at the end, fields can overflow freely: 90 minutes or 36 hours in a single box is fine.
Decimal hours are the form payroll, billing and project-tracking systems use. The fractional part is a share of an hour, not a count of minutes, so 7.75 hours is 7 hours 45 minutes and 1.2 hours is 1 hour 12 minutes. A common error is to read 7.45 hours as 7:45; it is actually 7 hours 27 minutes.
Clock arithmetic works on a 24-hour circle. When the end time is earlier than the start, the end is taken to be on the next day, and when a duration pushes a time past midnight the result says how many days it moved. If you supply a start date, the result date and weekday are shown too. Daylight-saving changes are ignored, which matches how most schedules are written, but on the night clocks change the real elapsed time differs by an hour.
Common use cases
Totalling video or audio clips
Add up the running times of tracks, lectures or edit segments to see the full length.
Billing and timesheets
Convert logged h:mm into decimal hours before multiplying by an hourly rate.
Travel and shift planning
Find when a long drive, flight or shift will finish, even when it runs into the next day.
Training logs
Sum workout or practice sessions across a week, or subtract rest periods from a total.
Tips and limitations
- Enter every field as a positive number and use the sign button for subtraction; the total can still go negative.
- Seconds accept decimals, so lap or split times such as 12.35 seconds add correctly.
- For a full weekly time card with breaks and overtime, use the Time Card Calculator instead.
- For the number of days between two calendar dates, use the Date Difference tool; this calculator works with clock times and durations.
- Clock results ignore daylight-saving shifts. Check the local clock change if a calculation spans that night.
Frequently asked questions
How do you add hours and minutes together?
Add the minutes, and for every 60 minutes carry one hour; then add the hours. 2 h 45 m + 1 h 30 m is 3 h 75 m, which becomes 4 h 15 m. The calculator does the same with seconds and days.
How do I convert hours and minutes to decimal hours?
Divide the minutes by 60 and add them to the hours. 7 hours 45 minutes is 7 + 45/60 = 7.75 hours. With seconds, also add seconds / 3,600.
What is 7.45 hours in hours and minutes?
0.45 of an hour is 0.45 x 60 = 27 minutes, so 7.45 hours is 7 hours 27 minutes. It is not 7:45, which would be 7.75 hours.
How do I calculate the time between two times that cross midnight?
Add 24 hours to the end time before subtracting. From 22:15 to 06:40 is 30:40 - 22:15 = 8 hours 25 minutes. The calculator does this automatically when the end is earlier than the start.
What time will it be in a given number of hours?
Use the "Add time to a clock time" mode: enter the start time and the hours and minutes to add. It shows the resulting time and whether it is the next day or later; add a start date to see the exact date and weekday.
Can I subtract time with this calculator?
Yes. In the durations mode press the plus button on any row to turn it into a minus, and in the clock mode choose Subtract. Totals can go below zero and are shown with a minus sign.
Is there an in-depth guide to the Time Calculator?
Yes. “Age, Time Cards and Time Arithmetic: How the Counting Works” covers the background, how it works, common pitfalls and worked examples. Read the full guide.
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