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Time Calculator

Add and subtract hours, minutes, and seconds across up to 20 rows, or find the time a set number of hours and minutes before or after a clock time. This time calculator gives totals as HH:MM:SS, in decimal hours, and in minutes.

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Calculate
Times to add or subtract (empty fields count as 0)

Operation

Show times as
Total time
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How to use the Time Calculator

Add up times

  1. Choose Add up times.
  2. Enter days, hours, minutes, and seconds in the first row. Empty fields count as 0.
  3. In the next row, choose + or − and enter the time to add or subtract. Press Add row for more entries, up to 20.
  4. Press Calculate. The total appears as HH:MM:SS, with decimal hours, total minutes, and total seconds underneath.

Work from a clock time

  1. Choose From a clock time.
  2. Enter the start time, for example 3:50 PM.
  3. Pick Add or Subtract, then enter the hours and minutes.
  4. Read the new time. If it falls on the next or previous day, the Day line says so.

How it works

In the first mode, every row is turned into seconds. The rows are added or subtracted, and the total is split back into days, hours, minutes, and seconds.

rowSeconds = D × 86400 + H × 3600 + M × 60 + S
total = Σ (sign × rowSeconds)
  • D, H, M, S: the days, hours, minutes, and seconds in one row
  • sign: +1 for a row you add, −1 for a row you subtract
  • total: the result in seconds. Its absolute value is split into days, hours, minutes, and seconds, and a minus sign is added when it is negative.

Decimal hours are the total seconds divided by 3,600, shown to 4 decimal places.

In the clock mode, the start time is counted in seconds from midnight. The hours and minutes are added or taken away, and the result is wrapped around the 24-hour clock.

t = start ± (H × 3600 + M × 60)
new time = t mod 86400
day change = floor(t ÷ 86400)

A day change of 1 means the new time is on the next day, and −1 means the day before.

Examples

  • 2:45:30 + 1:30:45 = 4:16:15. That is 4.2708 hours, 256.25 minutes, or 15,375 seconds.
  • 8:00:00 − 2:45:30 = 5:14:30.
  • A row of 0 hours and 90 minutes is normalized to 1:30:00.
  • 30 minutes from 3:50 PM is 4:20 PM.
  • 15 minutes after 11:09 is 11:24.
  • 10:45 PM plus 2 hours 30 minutes is 1:15 AM on the next day.
  • 45 minutes before 12:20 AM is 11:35 PM on the previous day.

30 minutes from 3:50 PM, in the calculator

Time Calculator in From a clock time mode: start time 3:50 PM, add 0 hours and 30 minutes, result 4:20 PM, 16:20 on the 24-hour clock, same day
From a clock time: 3:50 PM plus 30 minutes.

The From a clock time mode with the FAQ example: 3:50 PM plus 30 minutes is 4:20 PM, 16:20 on a 24-hour clock, on the same day. This example is one of the automated tests for the tool, so a code change that gives a different answer fails the test run.

Why you can't add time like ordinary numbers

Time counts in sixties, not tens, so a normal calculator gives the wrong answer. 1:30 plus 1:45 is 3:15. Type 1.30 + 1.45 into a standard calculator and you get 2.75, which reads like 2 hours and 75 minutes.

Decimal hours are something else again. 1:30 is 1.5 hours, because 30 minutes is half an hour. Payroll and invoicing systems usually want decimal hours, while schedules and video lengths use hours and minutes. The calculator shows both, so you can paste whichever format the other system expects.

Clock times add one more trap: the hour wraps at 12 or 24. 40 minutes after 11:50 is 12:30, not 11:90, and on a 12-hour clock it also flips between AM and PM. The clock mode handles the carry and tells you when the answer moves to another day.

Common uses

  • Adding up the lengths of video or audio clips
  • Totalling time spent on tasks for an invoice
  • Subtracting breaks from a block of time
  • Working out when a 45-minute meeting, a bake, or a parking ticket ends
  • Finding when to leave so you arrive 1 hour 20 minutes before a departure

Limitations

  • Each field takes a whole number from 0 to 99,999. Decimals and negative numbers are rejected. To take time away, use the − operation or Subtract.
  • Minutes and seconds above 59 are allowed and carried over automatically.
  • If you subtract more than you add, the total is negative and shown with a minus sign.
  • The clock mode works with hours and minutes on a plain 24-hour clock. It does not know about dates, time zones, or daylight saving changes.
  • For the gap between two clock times, such as 09:15 to 17:40, use the time duration calculator.

Read the guide

Add time and count days between dates

Add hours, minutes, and seconds correctly, count the days between two dates with or without the end date, and find a date's day number.

Frequently asked questions

How do I add hours and minutes together?

Add seconds, then minutes, then hours. Every 60 seconds carries 1 minute, and every 60 minutes carries 1 hour. The calculator does this for up to 20 rows.

What time will it be 30 minutes from 3:50?

4:20. Add the 30 minutes to the 50 to get 80, then carry 60 of them into the hour. The From a clock time mode does this for any time.

How do I subtract minutes from a time?

Switch to the From a clock time mode, enter the start time, pick Subtract, and enter the minutes. 45 minutes before 12:20 AM is 11:35 PM on the day before.

What happens if I enter more than 59 minutes?

The extra minutes are converted into hours automatically. For example, 90 minutes becomes 1 hour 30 minutes.

Can the result be negative?

Yes. If you subtract more time than you add, the total is shown with a minus sign.

How do I convert the total to decimal hours?

Divide the minutes by 60 and the seconds by 3,600, then add them to the hours. The decimal value is shown under the main result.

Often used together with Time Calculator.