Add Days Calculator

1. How to add days to a date
2. Practical applications of adding days
3. What day will it be in X days?
4. What calendar is used to add days to a date

This add days calculator is a simple tool you can use when you need to add or subtract days to/from a specific date; or in other words, to see which date it will be after N days have passed, or which date it was N days before any given date. The date format adjusts automatically depending on your browser locale settings.

    How to add days to a date

Adding days to a date is required if you want to find out what date it will be 30 days from now, for example. To calculate it, write the number '30' in the second field. If the date is different from the current one, let's say Feb 20, 2026, write it in the first field. Then click on 'Calculate'. In this case the result would be Mar 22, 2026. Note that the same calculation in the year 2024 will yield Mar 21, 2024 since it is a leap year and February has 29 days.

Despite its name, you can also use the add days calculator to subtract, for example, 90 days from a specific date. First, make sure the right date is entered in the date field and then write '-90' in the second field. If we subtract 90 days from Feb 20, 2026 the result would be Nov 22, 2025.

With both days addition and subtraction, if the time interval is expressed in terms of weeks, months, years, or decades, it is first necessary transform these into a number of days before performing the operation. It is easy to do with weeks (1 week = 7 days), but the other time measures have variable length so the exact number of days will vary depending on the calendar.

    Practical applications of adding days

Adding days is useful in many everyday situations. Let's say you ordered custom furniture and you were given a 45-day completion term. With this calculator for adding days to a date, you can easily see when you can expect your furniture to be ready which is 45 days from today. Just add 45 days to the current date, whatever it happens to be. If the time was given in business days, make sure to use our working days calculator instead!

Another common case when you need to add days is when you want to return a purchase or make use of a guarantee for a given product. Say you have a 14-day free return period and you know you made the purchase on Dec 20, 2025. You enter this date in the date field, then enter 14 in the "days to add" field and the day adder will tell you that you have until end of day on Jan 3, 2026 to return the product.

In another example, maybe you were prescribed medication to take for 10 days, after which you need to visit your GP for evaluation of the treatment. Just enter the date you started taking your medication in the "Date" field and 10 in the "days to add" field of the add days calculator to learn the date after which you should go see your physician again.

    What day will it be in X days?

A typical use of a day adder is to check what day of the week it will be in a given number of days. For example, to see what day it will be in 10 days, enter "10" in the "Days to add" field before pressing "Calculate" to see the date plus 10 days. You see both the resulting date, and the day of the week (Sunday through Monday) it will be. Likewise you can check what day it will be in 5 days, 20 days, or any number of dates.

A trick you can use to get the answer by mental calculation is to check if the number of days to add is wholly divisible by seven. If it is, then it will be exactly the same day of the week. For example, if the question is "what day will it be in 7 days" and it is Tuesday today, it will be Tuesday in seven days as well. Likewise it will be Tuesday in 14, 21, or 28 days.

    What calendar is used to add days to a date

This tool uses the Gregorian calendar, currently the most widely used calendar in the world. It is solar-based system of time-keeping. The mean length of its year is 365.25 days. To make it dividable into days it every three years in a row have 365 days and the forth one, also called leap year, has 366 days. To achieve this, one more day added to February.

Currently, our add days to date calculator only supports the internationally recognized calendar and does not support more ezoteric ones like the Lunar calendar, the Islamic calendar, or Lunisolar calendars of any kind. Do let us know if that is something you would like to see us do!