Add Hours Calculator

How to use the add hours calculator

This tool answers a simple question: what will the clock read after a stretch of time has been added to, or taken away from, a starting time? It suits planning a task that starts at 10:30 and runs for a few hours, working out when a night shift ends, or finding the time to set off so you arrive when you need to.

1. Choose Add hours & minutes to move forward, or Subtract hours & minutes to move back.
2. Enter the starting time in the time box.
3. Type the number of hours and the number of minutes. Either box can stay empty, but the total must be more than zero.
4. Press the button. The answer appears as a 24-hour time and as a 12-hour time with AM or PM.

When the result falls on a different calendar day, an extra row with the full date and time is added above the clock times, and the clock times carry a short note such as "the next day" or "2 days ago". The note counts real calendar days, so it stays right across a month or year end: 22:00 on 31 December plus 3 hours reads 01:00, the next day.

How the time arithmetic works

A clock repeats every 24 hours, so the sum is done in minutes since midnight and wraps around at 1,440, which is 24 × 60.

result = (start + added) mod 1,440All values in minutes since midnight. For subtraction, use start − removed and add 1,440 if the answer is negative.

Adding within a day. Start at 10:30, which is 630 minutes. Adding 5 hours 45 minutes (345 minutes) gives 975 minutes, and 975 ÷ 60 = 16.25, so the time is 16:15, or 4:15 PM.

Adding across midnight. Start at 22:30 (1,350 minutes) and add 5 hours 45 minutes. The total is 1,695, which is more than a day, so subtract 1,440 and keep 255 minutes. That is 4 hours 15 minutes after midnight: 04:15 the next day.

Subtracting across midnight. Start at 02:15 (135 minutes) and take away 3 hours 30 minutes (210 minutes). The result is −75, so add 1,440 to get 1,365 minutes, which is 22:45 on the previous day.

Entering decimal hours

The hours box accepts decimals, so 2.5 means two and a half hours. To see what a decimal means in minutes, multiply the part after the point by 60. The tool rounds fractional hours to the nearest whole minute, while the minutes box ignores anything after the decimal point, so a typed 1.9 counts as 1 minute.

For longer lists of conversions, the decimal to time converter goes in both directions.

12-hour and 24-hour clocks

The 24-hour clock numbers the hours from 00 to 23. Midnight is 00:00, noon is 12:00, and every hour after noon is the 12-hour value plus 12. The 12-hour clock restarts at 12 after midnight and again after noon, with AM marking the morning half and PM the afternoon half. The two are easy to confuse around 12: 12:30 AM is half an hour after midnight, while 12:30 PM is half an hour after noon.

The 24-hour to 12-hour converter and the military time converter handle a single time on its own.

Days, time zones and daylight saving

The calculation is pure clock arithmetic. It does not know which time zone you are in, and it does not model the hour that is skipped or repeated when clocks change for daylight saving. If your span crosses a change, 22:00 plus 8 hours reads 06:00 on the wall clock, even though only 7 or 9 real hours may have passed. Use the time zone converter to translate a result into another place.

When the result lands on another day, read the full date row as the authoritative answer. For spans measured in days rather than hours, the add days calculator is easier to follow, and the time calculator adds and subtracts whole durations.

A common slip is reading 1.30 hours as one hour thirty minutes. It is 1.30 × 60 = 78 minutes, which is 1 hour 18 minutes. Enter 1 hour and 30 minutes in the two boxes if that is what you mean.

Related tasks

• Finding the gap between two clock times: use the hours between times calculator.
• Working out what time it will be a set number of hours from this moment: try the hours from now calculator.
• Totalling shifts across a week: see the work hours timesheet calculator.