Date Calculator: Add or Subtract Days, Months, Years
Add years, months, weeks and days to a date, or subtract them, and see the resulting date and weekday. Month-end cases such as 31 January plus one month follow the rule in Turkish law.
- Day of the weekTuesday
- Days between30 days
- Day of the year335
- ISO weekWeek 49 (2026)
How it is calculated
The Code of Obligations (Art. 92), the Civil Procedure Code (Art. 92) and the Tax Procedure Law (Art. 18) set the same rule: a period in months or years ends on the matching day of the last month, or on that month’s last day if it lacks one. The “end to end” option is not in the statutes and is for contracts that set such a rule: it makes a period starting on a month’s last day also end on a last day (30 April + 1 month = 31 May). To see whether a due date falls on a holiday and moves, use the due date calculator.
Result = (Date ± Years×12 + Months months) ± (Weeks×7 + Days) daysMonths and years go first: the day number is kept, and if the month reached lacks it, its last day is used. Weeks and days are then added as calendar days, leap years included.- Turn years into months and add the months.
- Move the start date’s month that far forward (or back), keeping the day number.
- If the month reached lacks that day, take its last day.
- Add weeks × 7 plus days as calendar days.
Example
15 January 2025 + 3 months 10 days: 15 April 2025 + 10 days = Friday 25 April 2025. 31 January 2025 + 1 month: February has no 31st, so 28 February 2025.
Frequently asked questions
What is the date 90 days from today?
The start date opens on today; type 90 in the days field. Adding 3 months can give a different date, since months run 28–31 days.
What is 29 February plus one year?
If the next year is not a leap year it has no 29 February, so the result is 28 February (the last-day rule).
Does the order matter when adding months and days?
Yes. This tool adds years and months first, then weeks and days: 31 January + 1 month + 1 day = 1 March (28 February + 1 day).