Time Calculator
Add and subtract hours, minutes and seconds, or add time to a clock time — with overnight rollovers, decimal hours and the full working.
Time Calculator
How to use the time calculator
Add or subtract durations totals any number of time lengths — video clips, laps, work sessions, recipe steps. Type hours, minutes and seconds in each row (leave boxes you don’t need empty, and use decimals like 1.5 hours if you like), switch a row to “−” to subtract it, and add up to ten rows. Clock time ± duration answers “what time will it be?” and “what time was it?”: pick a start time, add or subtract a duration, and see the clock time with a note when it lands on another day. Results appear as you type, in hours:minutes:seconds and in decimal hours and minutes, and the page address keeps your numbers so you can share them.
The formulas
row seconds = hours × 3,600 + minutes × 60 + seconds
total seconds = sum of the + rows − sum of the − rows
h:mm:ss = total ÷ 3,600 (whole hours), remainder ÷ 60 (minutes), what is left (seconds)
decimal hours = total seconds ÷ 3,600
clock ± time = start (in minutes after midnight) ± duration, then ∓ 1,440 for each midnight crossed Converting everything to one unit first is what makes time arithmetic reliable: hours and minutes carry at 60, not 100, so you can’t add them like ordinary decimals.
Worked examples
Adding durations (the example in the calculator): 2 h 45 min 30 s + 1 h 20 min 45 s. In seconds that is 2 × 3,600 + 45 × 60 + 30 = 9,930 s and 1 × 3,600 + 20 × 60 + 45 = 4,845 s, so the total is 14,775 s. Dividing by 3,600 gives 4 hours with 375 s left over, and 375 s is 6 minutes 15 seconds: 4:06:15. In decimal form that is 14,775 ÷ 3,600 ≈ 4.1042 hours, or 14,775 ÷ 60 = 246.25 minutes.
Adding to a clock time: 10:45 PM + 3 h 30 min. 10:45 PM is 22:45, which is 22 × 60 + 45 = 1,365 minutes after midnight, and 3 h 30 min is 210 minutes. 1,365 + 210 = 1,575 minutes — more than the 1,440 minutes in a day — so subtract 1,440 to get 135 minutes into the next day: 2 h 15 min, or 2:15 AM the next day.
Why 1:45 + 1:30 isn’t 2:75
Treating times as decimals is the most common mistake. 1:45 + 1:30 = 2:75 looks right until you remember that there are only 60 minutes in an hour: 75 minutes is 1 hour 15 minutes, so the answer is 3:15. The same goes for decimal hours — 1.45 hours is 1 hour 27 minutes, not 1 hour 45 minutes. Keep hours:minutes and decimal hours clearly apart; payroll and invoices usually want decimals (1:45 = 1.75 h), stopwatches and video editors use h:mm:ss.
| Minutes | Decimal hours | Minutes | Decimal hours |
|---|---|---|---|
| 6 | 0.1 | 30 | 0.5 |
| 15 | 0.25 | 40 | 0.6667 |
| 20 | 0.3333 | 45 | 0.75 |
| 24 | 0.4 | 50 | 0.8333 |
Tips
- Timesheets: to total shifts with start and end times, breaks and overtime, use the hours calculator.
- Days between dates: for whole days, weeks and months use the date difference calculator.
- 24-hour times: switch the result to the 24-hour clock above, or convert any time with the military time converter.
- Across time zones: a flight that leaves at 10:45 PM in New York and lasts 7 hours lands at 5:45 AM New York time — use the time zone converter to see that as local time at the destination.
Frequently asked questions
How do I add hours and minutes?
Add the hours and the minutes separately, then carry every 60 minutes into an hour. 1 h 45 min + 2 h 30 min = 3 h 75 min, and 75 minutes is 1 h 15 min, so the total is 4 h 15 min. The calculator does the same thing in seconds, so it also works with seconds and decimals.
How do I subtract one time from another?
Subtract the minutes first; if you can’t, borrow 1 hour as 60 minutes. 5 h 10 min − 2 h 45 min: borrow an hour to make 4 h 70 min, then 70 − 45 = 25 minutes and 4 − 2 = 2 hours, so the answer is 2 h 25 min. Set a row to “−” to subtract it.
What time will it be in 12 hours?
The same clock time with AM and PM swapped: 9:30 PM + 12 hours is 9:30 AM the next day. For any other amount, use the Clock time ± duration mode, which also tells you if the answer lands on the next or previous day.
How do I convert hours and minutes to decimal hours?
Divide the minutes by 60 and add them to the hours: 2 h 45 min = 2 + 45 ÷ 60 = 2.75 hours. With seconds, divide them by 3,600. Every result on this page is also shown in decimal hours and in minutes.
How many hours is 150 minutes?
150 ÷ 60 = 2.5 hours, or 2 hours 30 minutes. Type 150 in a row’s minutes box and the calculator shows both forms. For quick unit swaps there is also a minutes to hours converter.
Does the calculator account for daylight saving time?
No. It does clock arithmetic — the way you would count on a watch face — which is what you want almost always. On the two nights a year when clocks change, the real elapsed time differs by an hour: 8 hours after 10:00 PM on the night clocks spring forward, a clock reads 7:00 AM, not 6:00 AM. The time zone converter handles those dates exactly.