Date Add / Subtract Calculator

The Date Add and Subtract Calculator computes a future or past date by adding or subtracting any number of days, weeks, months or years from a starting date. It is essential for project management, legal and contract deadline calculation, event planning, tracking notice periods and calculating expiry dates for subscriptions, warranties or documents. The calculator correctly handles leap years, varying month lengths and day-of-week information.

Date arithmetic is surprisingly complex because months have different lengths (28 to 31 days), years can be leap years (adding one day to February), and results must account for these variations consistently. Adding 1 month to January 31 yields February 28 (or 29 in leap years) — not a date 31 days later. This distinction matters critically in legal contracts, where "one month from January 31" and "31 days from January 31" produce different dates. Our calculator handles all these edge cases correctly according to standard calendar arithmetic rules.

Business day calculations (excluding weekends) are frequently needed for employment contracts, financial transactions and regulatory filings. A 30-day notice period starting Friday January 10 ends on Sunday February 9, meaning the last working day is Friday February 7. Use our Days Between Dates calculator to verify durations, and our Week Number Calculator to identify the ISO week of any result date. Free, no registration required.