About this date calculator
Working out the date 90 days from now, or six months before a deadline, means counting across months of different lengths and leap years. This calculator does it exactly. Enter any combination of years, months, weeks, and days and it applies them in that order, so you can follow each step. When adding months would land on a day that does not exist, such as 31 February, it uses the last day of the month instead. Alongside the result you get its weekday, ISO week number, quarter, and day of the year, plus how many business days and weekend days lie in between.
How to add or subtract from a date
- Choose the start date. Pick a Start date; it starts on today.
- Pick Add or Subtract. Choose Add to go forward in time or Subtract to go back.
- Enter the amounts. Type any mix of Years, Months, Weeks, and Days, or press an example such as +90 days.
- Press Calculate date. Read the resulting date and weekday, the days in between, and the step-by-step working.
Frequently asked questions
What happens when I add a month to 31 January?
February has no 31st, so the result is the last day of February: 28 February, or 29 February in a leap year. The same rule applies to any month that is shorter than the starting day.
In which order are the units applied?
Years first, then months, then weeks, then days. The order matters near month ends, so the step-by-step list shows the date after each unit.
How are business days between the dates counted?
Every Monday to Friday from the start date up to, but not including, the result date counts. Public holidays are not taken out, because they depend on the country.
Is a week always seven days here?
Yes. Weeks are added as exact blocks of seven days, so adding 2 weeks is the same as adding 14 days.
Which years can I use?
Any date from the year 1 to the year 9999, using the Gregorian calendar for all dates, including those before it was introduced in 1582.