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Miraç Özdemir
Date & Time

Add Months and Years to a Date

Add or subtract years, months and days from a date and get the result date with the month-end rule and its weekday — handy for due dates.

Version 1

Things to keep in mind:

  • Public holidays, weekend shifting and court recess are not considered; do not use it for statutory or service deadlines.
  • If a contract defines a "month" differently (e.g. 30 days), follow that definition; the tool uses calendar months.

Calculator

Start

The date to add to (1900–2199). To start from today, pick today's date.

Period to add

Negative values subtract from the date.

Years to add; enter a negative value to subtract (e.g. -1). Whole number from -200 to 200.

Months to add; enter a negative value to subtract. Values above 12 are accepted (e.g. 18 months).

Days added after the years and months; enter a negative value to subtract.

After the first calculation, the result updates automatically when you change a value.

Result

Enter the values and press Calculate to see the result here.

About this tool

This tool adds years, months and days to a start date (negative values subtract) and returns the result date, the weekday it falls on and the number of calendar days between start and result. It answers questions like "what date is 3 months from now?" for contract ends, rent periods, instalments or due dates.

How it works

  1. Total months = years × 12 + months
  2. Intermediate date = start date + total months (calendar months)
  3. Result date = intermediate date + days

Month-end rule: if the target month has no such day, the result moves to that month's last day. 31 January + 1 month is 29 February in a leap year and 28 February otherwise; 29 Feb 2024 + 1 year = 28 Feb 2025. Adding a month is therefore not the same as adding 30 days — use the add-days tool for a fixed number of days.

Years and months are applied first, days last. The order can matter: 31 March − 1 month = 28 February, then − 5 days = 23 February.

Example

3 October 2026 + 1 year 2 months 10 days: 14 months → 3 December 2027; + 10 days → 13 December 2027, weekday code 1 (Monday). There are 436 calendar days from start to result.

The weekday uses ISO 8601 numbering: 1 = Monday … 7 = Sunday.

How to use

  1. Pick the start date.
  2. Enter the years, months and days to add; use negative values to subtract and leave unused fields at 0.
  3. Click Calculate.

Notes

Timezone-free Gregorian calendar. Years and months are added with the month-end rule (clamped to the target month's last day), days afterwards. Weekday: 1 = Monday … 7 = Sunday. The day difference is result minus start (negative when the result lies in the past).

Frequently asked questions

4 questions

  1. February has no 31st, so the result moves to the month's last day: 29 February in a leap year, 28 February otherwise.

Next step

Related tools to continue your calculation.

  • Add or Subtract Days from a Date

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  • Day of the Week Calculator

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  • Weekday Count Between Dates

    Count the weekdays between two dates, excluding Saturdays and Sundays. Public holidays are not taken into account; only weekends are removed.

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