How to use the time calculator
- Choose a mode: “Add or subtract” for two durations, “Time after” for a clock time plus or minus a duration, or “Convert” to change units.
- Enter the numbers in the days, hours, minutes and seconds boxes. Blank boxes count as zero, and decimals such as 1.5 hours are fine.
- Pick add or subtract. In “Time after” mode you can also choose a starting weekday to see which day the result lands on.
- Read the result, normalized into days, hours, minutes and seconds, with totals in each unit. Copy the link to share it.
How to add time by hand
Time is not written in base 10: 60 seconds make a minute, 60 minutes make an hour and 24 hours make a day. So you add each unit separately, starting with the smallest, and carry whenever a column reaches 60 (or 24 for hours, if you want days).
| Hours | Minutes | Seconds | |
|---|---|---|---|
| First duration | 2 | 45 | 30 |
| Second duration | 1 | 30 | 45 |
| Column sums | 3 | 75 | 75 |
| After carrying | 4 | 16 | 15 |
The seconds add to 75, which is 1 minute and 15 seconds, so write 15 and carry 1 to the minutes. The minutes become 45 + 30 + 1 = 76, which is 1 hour and 16 minutes, so write 16 and carry 1 to the hours. The hours become 2 + 1 + 1 = 4. The total is 4 hr 16 min 15 sec, or 4:16:15.
A common everyday case is adding up shifts. Two shifts of 8:45 and 7:50 add to 15 hours and 95 minutes, which regroups to 16 hr 35 min, not 15.95 hours.
The shortcut: convert everything to seconds
This calculator avoids carrying mistakes by turning each duration into whole seconds, doing one addition or subtraction, and then splitting the total back into units.
Total seconds T = 86,400 × days + 3,600 × hours + 60 × minutes + seconds
- d, h, m, s
- days, hours, minutes and seconds
- T
- the duration in seconds; divide by 86,400, then 3,600, then 60, keeping remainders, to split it back
For the example above: 9,930 seconds + 5,445 seconds = 15,375 seconds. Then 15,375 ÷ 3,600 = 4 hours with 975 seconds left over, and 975 ÷ 60 = 16 minutes with 15 seconds left, which is 4:16:15.
How to subtract time
Subtract from the smallest unit up. When a column on top is smaller than the one below, borrow 1 from the next larger unit and add 60 (or 24 when borrowing a day into hours). To take 1 hour 45 minutes from 3 hours 10 minutes, borrow an hour: 3:10 becomes 2 hours 70 minutes. Then 70 − 45 = 25 minutes and 2 − 1 = 1 hour, for 1 hr 25 min. If the second duration is longer than the first, the calculator shows a negative result, which you can read as a shortfall.
What time will it be after a duration?
Adding a duration to a clock time works the same way, except the clock wraps around every 24 hours. Convert the start to 24-hour time, add, and subtract 24 hours (moving one day forward) for every full day that passes.
- 10:30 PM + 5 hr 45 min = 4:15 AM, +1 day (next day).
- 1:00 AM − 3 hr = 10:00 PM, −1 day (previous day).
- Friday 9:00 AM + 3 days 1 hr = Monday 10:00 AM.
The calculator does clock arithmetic only. It does not know your time zone or daylight saving time, so across a clock change the real result can be an hour off. To count days between calendar dates, use the date calculator.
24-hour vs. 12-hour time
The 12-hour clock runs from 12 AM (midnight) to 11:59 AM, then from 12 PM (noon) to 11:59 PM. The 24-hour clock numbers the hours 00 to 23, so no AM or PM is needed. To convert an afternoon or evening time from 24-hour form, subtract 12 from the hour. The two special cases are 00:00, which is 12:00 AM, and 12:00, which is 12:00 PM.
| 24-hour | 12-hour |
|---|---|
| 00:00 | 12:00 AM (midnight) |
| 01:00 | 1:00 AM |
| 02:00 | 2:00 AM |
| 03:00 | 3:00 AM |
| 04:00 | 4:00 AM |
| 05:00 | 5:00 AM |
| 06:00 | 6:00 AM |
| 07:00 | 7:00 AM |
| 08:00 | 8:00 AM |
| 09:00 | 9:00 AM |
| 10:00 | 10:00 AM |
| 11:00 | 11:00 AM |
| 12:00 | 12:00 PM (noon) |
| 13:00 | 1:00 PM |
| 14:00 | 2:00 PM |
| 15:00 | 3:00 PM |
| 16:00 | 4:00 PM |
| 17:00 | 5:00 PM |
| 18:00 | 6:00 PM |
| 19:00 | 7:00 PM |
| 20:00 | 8:00 PM |
| 21:00 | 9:00 PM |
| 22:00 | 10:00 PM |
| 23:00 | 11:00 PM |
Time unit conversions
Seconds, minutes, hours, days and weeks have fixed lengths, so converting between them is a single multiplication or division. Months and years vary (28 to 31 days, 365 or 366 days), so they are best handled with calendar dates.
| Unit | Seconds | Minutes | Hours | Days |
|---|---|---|---|---|
| 1 minute | 60 | 1 | 0.016667 | 0.000694 |
| 1 hour | 3,600 | 60 | 1 | 0.041667 |
| 1 day | 86,400 | 1,440 | 24 | 1 |
| 1 week | 604,800 | 10,080 | 168 | 7 |
Work hours are often written as decimals. To turn minutes into a decimal fraction of an hour, divide by 60. The hours calculator uses the same conversion for time cards, and the scientific calculator handles any other arithmetic.
| Minutes | Decimal hours | h:mm |
|---|---|---|
| 5 min | 0.0833 | 0:05 |
| 10 min | 0.1667 | 0:10 |
| 15 min | 0.25 | 0:15 |
| 20 min | 0.3333 | 0:20 |
| 30 min | 0.5 | 0:30 |
| 40 min | 0.6667 | 0:40 |
| 45 min | 0.75 | 0:45 |
| 50 min | 0.8333 | 0:50 |
Frequently asked questions
How do you add hours and minutes?
Add the hours and the minutes separately, then carry every 60 minutes into an hour. For 2 hr 45 min 30 sec plus 1 hr 30 min 45 sec, the seconds add to 75 (1 minute 15 seconds), the minutes to 76 (1 hour 16 minutes) and the hours to 4, giving 4 hr 16 min 15 sec.
How do you subtract time?
Subtract seconds, then minutes, then hours. When the top number is smaller, borrow 1 from the next unit up and add 60 to the one you are working on. For 3 hours 10 minutes minus 1 hour 45 minutes, borrow an hour to get 2 hours 70 minutes; 70 − 45 = 25 minutes and 2 − 1 = 1 hour, so the answer is 1 hr 25 min.
What time will it be in a certain number of hours?
Add the hours to the current time in 24-hour form, and if the result is 24 or more, subtract 24 and move to the next day. 10:30 PM is 22:30; adding 5 hr 45 min gives 28:15, which is 04:15 (4:15 AM) the next day. Choose the “Time after” mode to do this with any duration.
How many seconds are in a day?
A day has 86,400 seconds: 24 hours × 60 minutes × 60 seconds. An hour has 3,600 seconds, and a week has 604,800 seconds, or 10,080 minutes. These fixed values are what the converter uses. Months and years are not fixed lengths, so they are left out of the conversions.
How do I convert 24-hour time to 12-hour time?
For hours 13 to 23, subtract 12 and add PM, so 15:30 is 3:30 PM. Hour 12 stays 12 and is PM (noon), hour 00 becomes 12 AM (midnight), and hours 1 to 11 keep their number with AM. Minutes and seconds never change. The 24-hour format, often called military time in the U.S., avoids mixing up morning and evening.
How do I convert minutes to decimal hours?
Divide the minutes by 60. For example, 45 minutes is 45 ÷ 60 = 0.75 hours, so 7 hours 45 minutes is 7.75 hours. The converter here shows 2 hr 30 min as 150 minutes. For payroll time cards with breaks and overtime, use the hours calculator.