How to Use: Date and Time Calculator

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 Remove the time link takes you to the Date Calculator where you can execute the same type of calculation without including the time of day and without the option to add or subtract smaller time units like hours, minutes, or 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. Note that this calculator does not offer the option to specify the time of day or to add or subtract smaller time units like hours, minutes, or seconds.

The many input fields of the Date and Time Calculator can be confusing, especially when you view it on a small screen. As a general rule,

• the fields using the singular form of the time unit names, such as Day and Hour, are used to define the starting point for your calculation—i.e., the date and time of day you wish to add to or subtract from;
• and the fields using the plural form, such as Years and Hours, refer to the time units you wish to add or subtract.

We apologize for the inconvenience and will try to find a better solution for small screens.

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.

Our system supports both 24-hour and 12-hour (am/pm) clock formats. To change the format, please go to My Units and make a selection in the Time Format drop-down, and click Save Settings.

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.

1. Calculating the duration between 2 points in time:
   • Date to Date Calculator: Count days, weeks, months, and years between 2 dates.
   • Business Days Calculator: Count working days or non-working days between 2 dates.
   • Time Duration Calculator: Count days, hours, minutes, and seconds between 2 dates and times of the day.
   • Time Zone Duration Calculator: Count days, hours, minutes, and seconds between a point in time in one time zone and another point in time in another time zone.
2. Adding or subtracting days:
   • Date Calculator: Add or subtract days, weeks, months, and years to or from a date.
   • Business Date Calculator: Add or subtract working days or non-working days.
   • Date and Time Calculator: Add or subtract days, hours, minutes, and seconds to or from a date and time of day.

The General FAQ Page answers your questions about timeanddate.com, our services, site-wide settings, customization options, advertising opportunities, and copyright policies.