How to use the date calculator
- Choose Add or subtract to find a future or past date, or Difference between dates to measure the gap between two dates.
- Pick a start date. It defaults to today.
- Enter any mix of years, months, weeks and days, and choose add or subtract.
- Read the result date, its day of the week, and how far it is from today.
How month and year math works
Days and weeks are simple: the calculator moves forward or back exactly that many days. Months and years follow the calendar instead, because months have different lengths. Adding one month to March 15 gives April 15.
When the starting day doesn't exist in the target month, the result moves to that month's last day. January 31 plus one month is February 28, or February 29 in a leap year. Years work the same way, so February 29, 2024 plus one year is February 28, 2025.
When you combine units, years and months are applied first, then weeks and days.
Examples
90 days after October 25, 2026 is Saturday, January 23, 2027.
January 31, 2026 + 1 month is Saturday, February 28, 2026.
6 weeks before June 1, 2026 is Monday, April 20, 2026.
Common uses
- Deadlines: find the date that is 30, 60 or 90 days after a contract, invoice or notice.
- Pregnancy and health: count weeks from a start date (always confirm with your doctor).
- Travel and visas: check when a 90-day or 180-day stay ends.
- School: work out how many weeks remain until exams or the end of term.
For an exact count of days, or to exclude weekends, use the days between dates calculator.
Frequently asked questions
What date is 90 days from today?
Set the start date to today, choose Add, and enter 90 days. The result appears instantly with its day of the week. Today is the default start date.
How does the calculator add months to the 31st?
If the target month is shorter, the result is the last day of that month. January 31 plus one month is February 28, or February 29 in a leap year.
Does the date calculator include leap years?
Yes. It uses the real calendar, so February 29 is counted in leap years like 2028.
Can I subtract days to find a past date?
Yes. Choose Subtract in the Operation menu, then enter the days, weeks, months or years to go back.
How do I find the time between two dates?
Switch to Difference between dates and pick both dates. You'll see the gap in years, months and days, plus the total days and weeks.