Date Add/Subtract Calculator
Add or subtract days, weeks, months, and years from a start date and see the resulting date.
Resulting date
August 17, 2026
Monday
ISO date
2026-08-17
Format YYYY-MM-DD.
Weekday
Monday
Day of the week of the result.
Total calendar days
30
Calendar days after the start date.
How This Calculator Works
Choose add or subtract
Add moves the date forward. Subtract moves it backward using the same amounts.
Order of operations
Years are applied first, then months, then weeks and days, so calendar boundaries stay predictable.
Weeks become days
Weeks are converted to days as weeks times seven before the day amount is applied.
Month-end clamping
If the start day does not exist in the target month, the result clamps to the last valid day of that month.
Leap years
February 29 plus one year lands on February 28 when the target year has no February 29.
Weekday-only mode
The day and week amounts are counted as weekdays, skipping Saturdays and Sundays. Holidays are not included.
Worked Examples
Add 30 days
Input: Jun 20, 2026 + 30 days
Result: Jul 20, 2026
Simple day addition across a month boundary.
Subtract 30 days
Input: Jun 20, 2026 - 30 days
Result: May 21, 2026
The result moves earlier than the start date.
Add 1 month to the 31st
Input: Jan 31, 2024 + 1 month
Result: Feb 29, 2024
Clamped to the last valid day, a leap year February.
Add 1 month in a common year
Input: Jan 31, 2025 + 1 month
Result: Feb 28, 2025
Clamped to February 28 because 2025 is not a leap year.
Add 1 year to Feb 29
Input: Feb 29, 2024 + 1 year
Result: Feb 28, 2025
The non-leap year has no February 29.
Add 1 weekday
Input: Fri Jun 19, 2026 + 1 weekday
Result: Mon Jun 22, 2026
Saturday and Sunday are skipped in weekday-only mode.
Calendar Days vs Weekdays
Normal mode adds or subtracts every calendar day, including weekends. A result can land on any day of the week.
Weekday-only mode counts the day and week amounts as weekdays and skips Saturdays and Sundays. Years and months are always applied first as calendar units, so a result driven only by years or months can still fall on a weekend.
This calculator does not include public holidays. Holiday rules vary by country, region, and organization, so adjust the day amount manually if you need to account for specific holidays.
Common Date Math Mistakes
Frequently Asked Questions
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Related reading
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