Add Days to Date Calculator

1. Pick a start date. This defaults to today but you can set any past or future date as your starting point.
2. Choose Add or Subtract. Adding moves the date forward in time. Subtracting moves it backward, useful for finding deadlines or past dates.
3. Enter an amount and unit. Choose days, weeks, months, or years. For example, add 6 weeks to find a follow-up appointment date, or subtract 90 days to find a notice period start date.
4. The result shows the full date, day of week, and how many days from today that date falls.

Example: you signed a contract on March 1, 2025. Your 90-day review period ends on May 30, 2025 (a Friday). Enter March 1 as the start date, choose Add, enter 90 days, and the calculator confirms the end date and day of week.

Date addition and subtraction use calendar arithmetic, not simple day counting, when months and years are involved.

Adding days:    result = start date + N days
Adding weeks:   result = start date + (N × 7) days
Adding months:  add N to the month number, carry to year if needed
Adding years:   add N to the year number

Days from today = result date − today's date

Month-end edge cases: when you add one month to January 31, the result is February 28 (or 29 in a leap year) because February does not have 31 days. The calculator handles this correctly by snapping to the last valid day of the resulting month.

Common use cases and examples: