The Date Calculator allows you to calculate a date in the past or future by adding or subtracting any number of days, weeks, months, or years.
Jump to Frequently Asked Questions (FAQ)
Enable Repeat and enter a number into the field that appears to add or subtract the same number of days or other time units multiple times.
Example: To find out the dates 11, 22, 33, and 44 days from the start date, enter 11 into the Days field, tick the Repeat box, and enter 4 into the field.
The Include the time link takes you to the Date and Time Calculator where you can execute the same type of calculation, but including the time of day and the option to add hours, minutes, and seconds.
The Include only certain weekdays link takes you to the Business Date Calculator, which allows you to exclude public holidays or weekends from your calculation.
The calculator adds or subtracts the larger time units before the smaller time units. This means that it adds years, then months, then days. Although the total number of days in January (31) and February (28) are different both are counted as 1 month. In some cases, this method can lead to unexpected results.
For example, if you add one month and one day to March 1, the result is April 2, as is to be expected (March 1 + 1 month = April 1; April 1 + 1 day = April 2).
However, if you add one month and one day to February 28, which in a common year is the day before March 1, the result is March 29, which is 4 days before April 2. The reason is that the calculator first adds 1 month to jump from February 28 to March 28, then it adds one day to arrive at March 29. If it added the days first, the result would be April 1 (February 28 + 1 day = March 1; March 1 + 1 month = April 1).
This may seem illogical at first, but the structure of the modern calendar means that there is no perfect way of calculating dates including months and years.
For calculations with several possible results, the calculator shows the Alternative result below the primary result.
When adding or subtracting months, the Date Calculator keeps day numbers intact wherever possible. So, if you add 1 month to January 10, the result is February 10. Similarly, adding 1 month to February 10 results in March 10. The differing month lengths are ignored in this case.
However, this is not possible when subtracting 1 month from one of the last days in a month. Example: Subtract 1 month from May 31. The result in our calculator is April 30 because both dates represent the last day of the month. However, if you add 1 month to April 30, the result is May 30.
Got unexpected results? See “Why is the result wrong?” above.
Yes, all our calculators account for leap years.
No, this calculator does not account for leap seconds.
No, this calculator does not take DST changes into account.
You can change the order of the Day, Month, and Year fields by selecting a different Short Date format in My Units.
To edit your calculation, scroll up to the top of the page, make your changes, and calculate again. The Make adjustment and calculate again is a shortcut to the top of the page.
This is most likely not an error but due to the fact that the Julian calendar was still in use in the year you entered. This calendar system was eventually replaced by today's Gregorian calendar, but the date this change happened differed from one country to another.
The calculator uses the Julian-Gregorian switch date of the country you select in the settings under My Units.
Our Uses for the Date Calculators page provides some examples.
We are a small team with very extensive websites to manage, so, unfortunately, we do not have the capacity to share detailed information about our algorithms or provide programming help.
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