Time Calculator

Find what time it will be after a number of hours and minutes, what time it was before, or the total of two lengths of time.

End time
1:15 AM
Next day
24-hour time
01:15
Day
Next day
Duration
3:45:00 (3 hours, 45 minutes, 0 seconds)
Duration in decimal hours
3.75
  • 9:30 PM + 3:45:00 = 1:15 AM (next day)

Adding and subtracting time by hand

Time is counted in base 60, not base 10: 60 seconds make a minute and 60 minutes make an hour. Add hours to hours and minutes to minutes, then carry: every 60 minutes becomes 1 more hour. 9:45 plus 30 minutes is 9:75, which is 10:15.

Subtracting works the same way with borrowing. To take 50 minutes from 10:15, borrow an hour: 10:15 is 9:75, and 9:75 minus 50 minutes is 9:25.

On a clock, hours wrap around every 24. Going past midnight moves to the next day; going back before midnight moves to the previous day. The calculator tells you when that happens, and by how many days if the duration is longer than a day.

Durations versus clock times

A clock time is a moment (9:30 PM). A duration is a length (3 hours 45 minutes). You can add a duration to a clock time, or add two durations together, but adding two clock times — 9:30 PM plus 4:00 PM — has no meaning.

Durations aren't limited to 24 hours, so the duration result shows total hours: 30 hours is 30:00:00, not 6:00. The "in words" line also splits it into days.

To find the time between two clock times — for example, how long a shift lasted — use the hours calculator, which handles overnight shifts and unpaid breaks.

Decimal hours

Payroll and billing often use decimal hours, where 15 minutes is 0.25 hours and 45 minutes is 0.75 hours. To convert, divide minutes by 60: 3 hours 45 minutes is 3 + 45 ÷ 60 = 3.75 hours. Note that 3.45 hours is not 3 hours 45 minutes — it is 3 hours 27 minutes.

How the result is calculated

Duration in seconds = hours × 3,600 + minutes × 60 + secondsNew time = start time ± duration, then wrapped into one 24-hour dayDays moved = floor((start + duration) ÷ 86,400 seconds)
  • Decimal hours = total seconds ÷ 3,600.
  • Times ignore time-zone and daylight saving changes; on a clock-change night, actual elapsed time differs by an hour.

Worked examples

  1. A flight leaves at 9:30 PM and takes 3 hours 45 minutes. What time does it land (same time zone)?
  2. 9:30 PM is 21:30. Add 3 hours: 24:30. Add 45 minutes: 24:75, which is 25:15.
  3. 25:15 is past 24:00, so subtract 24 hours: 1:15 AM the next day (01:15 in 24-hour time).
  4. Adding durations: 2 hours 45 minutes 30 seconds plus 1 hour 30 minutes 45 seconds. Seconds: 30 + 45 = 75 = 1 minute 15 seconds. Minutes: 45 + 30 + 1 = 76 = 1 hour 16 minutes. Hours: 2 + 1 + 1 = 4. Total 4:16:15.

Frequently asked questions

What time will it be in 8 hours?

Enter the current time, choose "clock time + duration" and enter 8 hours. For example, 9:30 PM plus 8 hours is 5:30 AM the next day.

How do I subtract hours from a time?

Choose "clock time − duration". 2:15 AM minus 3 hours is 11:15 PM on the previous day — the calculator shows the day change.

How do I add up hours and minutes?

Add the minutes and convert every 60 into an hour. 2 hours 45 minutes plus 1 hour 30 minutes is 3 hours 75 minutes, which is 4 hours 15 minutes, or 4.25 decimal hours.

What is 3 hours 45 minutes in decimal hours?

3.75 hours. Divide the minutes by 60 and add them to the hours: 45 ÷ 60 = 0.75.

Does the calculator handle daylight saving time?

No. It does clock arithmetic, so it assumes every day is 24 hours. On the night clocks change, the real elapsed time between two clock times is an hour more or less.

Sources

Last reviewed for 2026. How we calculate.