Date Add/Subtract Calculator
Add or subtract days, weeks, months, or years from any date. Instantly find a future or past date, see the result's day of week, and count calendar days between start and result.
Formulas, assumptions, and rounding are documented in our calculator methodology.
Result Date
2026-06-16
Tuesday
Tuesday, June 16, 2026
Calculation Summary
- Start Date
- Sunday, May 17, 2026 (Sunday)
- Added
- 30 days
- Result Date
- Tuesday, June 16, 2026
- Day of Week
- Tuesday
- Calendar Days Between
- 30 days
Adding or subtracting months adjusts for month-end overflow — for example, January 31 + 1 month = February 28 (or 29 in a leap year). Calendar days shown are the total days between start and result. For counting working days, use the Business Days Calculator.
How Date Addition and Subtraction Works
Adding days is straightforward: add the number to the date's day-of-year count. Adding months is trickier — months have different lengths. This calculator adjusts for month-end overflow (January 31 + 1 month → February 28/29) and leap years automatically. Adding years works the same way, handling Feb 29 correctly in leap and non-leap years.
Common Use Cases for Date Arithmetic
Deadlines and notice periods: contracts often require 30-day or 90-day notice periods. Expiry dates: food safety, medication, and warranty expiry. Project planning: sprint end dates, milestone deadlines. Legal: statutes of limitations, filing deadlines, appeal windows. Finance: loan maturity dates, CD maturity, invoice due dates. Subscriptions: free trial expiry, renewal dates.
Month-End Overflow and Leap Year Handling
When adding months would push a date past the end of the result month, the calculator clamps to the last valid day. Examples: Jan 31 + 1 mo = Feb 28 (or 29). Jan 31 + 3 mo = Apr 30. Oct 31 + 1 mo = Nov 30. For leap years, Feb 28 + 1 yr = Feb 28 (non-leap) or Feb 28 (if not Feb 29). Date arithmetic in most programming languages and spreadsheets follows these same rules.
Frequently Asked Questions
- Enter your start date, select 'Add to Date,' enter the number of days, and make sure 'Days' is selected as the unit. The result date appears instantly, along with the day of week and total calendar days between the two dates.
- This calculator handles month-end overflow automatically. For example, January 31 + 1 month returns February 28 (or February 29 in a leap year) rather than March 2 or 3. This matches how most calendar and date arithmetic is done in finance, law, and everyday use.
- The Date Difference Calculator finds how many days, weeks, or months are between two dates you already know. This calculator goes the other direction — you know a starting date and a duration, and want to find the resulting date. Both tools are complementary.
- Yes. The calculator defaults to today's date as the start. Select 'Add to Date,' enter 30 (or 60 or 90) in the amount field, choose 'Days,' and the result date appears immediately. Use the quick preset buttons for common intervals.
- This calculator adds or subtracts calendar days (counting every day including weekends and holidays). For counting only working days, use the Business Days Calculator instead.