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Date Calculator: Add or Subtract Days, Weeks, Months, Years

This free date calculator adds or subtracts days, weeks, months and years from any starting date. It shows the new date and its weekday, and it handles month ends and leap years correctly.

By Debmedia Technologies LLP · Kolkata, India · Updated

What Is It and When Do You Need It?

Adding or subtracting time from a date answers questions such as "what is the date 90 days from now?". It is used for deadlines, warranties, notice periods, due dates and planning. Doing it by hand across months of different lengths is error-prone.

Choose a start date, whether to add or subtract, and any mix of years, months, weeks and days.

How to Use This Tool

  1. Pick the start date.
  2. Choose add or subtract.
  3. Fill in years, months, weeks or days.
  4. Press Calculate.

How the Calculation Works

Years and months are applied first, which moves the date by calendar months and clamps the day to the end of the month when needed. Then weeks and days are added or subtracted as exact numbers of days using calendar day numbers.

Worked Example

Adding 3 months and 10 days to 15 November 2026 gives 25 February 2027, a Thursday. Subtracting 100 days from 2 November 2026 gives 25 July 2026, a Saturday.

Common Uses

  • Deadlines and warranty end dates.
  • Notice and probation periods.
  • Planning trips and projects.
  • Medical and course schedules.

Tips and Common Mistakes

  • Blank boxes count as zero.
  • Negative numbers reverse the direction.
  • Check the weekday if a date must fall on a working day.
  • To count only working days between two dates, use the business days calculator, and remember that month lengths differ, so adding 30 days is not the same as adding one month.

Next, you may need the date difference calculator, business days calculator, day of the week calculator, days until calculator.

Everything runs in your browser. Nothing you type is uploaded, stored or sent to any outside service.

Frequently Asked Questions

Enter today’s date, choose Add and type 90 in the days box. The result shows the new date and weekday.
Adding one month to 31 January gives 28 February, or 29 in a leap year, because the day is limited to the last day of the target month.
Yes. Months and years are applied first, then weeks and days.
Yes, every calendar day counts. For working days only, use the business days calculator.

Disclaimer: results are calculated in your browser from the numbers you enter. Check important results before you rely on them for money, health, safety or legal decisions.