How to Calculate the Date & Time Difference

Written by c. taylor
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How to Calculate the Date & Time Difference
Windows 7's Calculator allows easy calculations for date and time differences. (Jeffrey Coolidge/Photodisc/Getty Images)

Calculating the difference between two dates is relatively easy for dates that are close together. However, doing so for dates months or years apart becomes more complicated. Luckily Windows 7 provides an excellent tool for calculating the difference between two dates with its included "Calculator." After the dates are subtracted, all that is left is simple arithmetic to calculate specific time differences. You may also use an online calculator to automatically calculate the difference

Skill level:
Moderately Challenging


    Calculating Date Differences

  1. 1

    Click "Start," type "Calculator" and click "Calculator" to open Window's Calculator. You may also navigate through "Start," "All Programs," "Accessories" and click "Calculator."

  2. 2

    Click "View" in the Calculator window and select "Date calculation," or you may simply press Ctrl and E simultaneously.

  3. 3

    Select the "From" and "To" dates using the drop down calendars on the right-hand side. Press "Calculate" and the difference will be displayed both in "year, months, weeks, days" format and in the cumulative "days" formats.

    Calculating Time Differences

  1. 1

    Convert the times to 24-hour time by adding 12 hours to any "p.m." date and dropping the colon. For example, 2:30 p.m. would be 1430, but 10:45 p.m. would just be 1045.

  2. 2

    Multiply the first two digits by 60 and add to the last two digits. This will give you the total minutes. For example, 1430 would be calculated as follows: 14 hours times 60 minutes per hour plus 30 minutes, which would equal 870 minutes.

    Likewise, 1045 would be calculated this way: 10 hours times 60 minutes per hour plus 45 minutes, which equals 645 minutes.

  3. 3

    Subtract the smaller total minutes from the larger one, but remember which time was the larger one. In the example, the difference would be 870 minutes minus 645 minutes, which equals 225 minutes.

    If the first date you entered into the Windows 7 calculator corresponded to the earlier time, and it occurred on a different day, then subtract the above result from 1,440, which is the number of minutes in a day. If that were the case in the current example, you would subtract 225 minutes from 1440 minutes to receive a difference of 1,215. You would also have to subtract one day from the Windows 7 date result, since there wasn't a full day between dates, and the time difference takes that into account.

  4. 4

    Convert to hours and minutes, if desired, by dividing by 60 and keeping any remainder as the minutes. In the example, 60 evenly goes into 225 three times (180) with a remainder of 45, so the converted difference is:

    3 hours, 45 minutes

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