Add or Subtract Days
Add or subtract days, weeks, months, or years from any starting date to determine a deadline or past event.
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How to Use the Add or Subtract Days
Enter the required values in the fields above and click Calculate. All calculations are executed directly inside your web browser using proven mathematical formulas, ensuring instantaneous results and 100% privacy without transmitting your numbers to remote servers.
Mathematical Formula
Target Date = Start Date ± (Offset Quantity × Time Unit)
Worked Example
Adding 45 days to October 1, 2025 yields Saturday, November 15, 2025.
Important Notes & Limitations
Month additions adjust to the last valid day of shorter months (e.g. adding 1 month to January 31 lands on February 28).
Frequently Asked Questions
Select your project start date and add the required number of working or calendar days.