How to Use the Date Calculator
The date calculator has two modes. In Add / Subtract mode, pick a start date, choose to add or subtract, and enter any combination of years, months, weeks, and days. The result shows the exact resulting date accounting for varying month lengths and leap years.
In Date Difference mode, enter two dates and instantly see how many days, weeks, months, or years separate them. Business days are also calculated by excluding weekends.
Common Date Calculations
| Use Case | Example |
|---|---|
| Contract deadlines | What date is 90 days from signing? |
| Pregnancy due date | 40 weeks from last menstrual period |
| Age eligibility | What date will I turn 65? |
| Warranty expiration | 12 months from purchase date |
| Project timeline | Days until deadline from today |
| Loan maturity | 5 years from origination date |
Leap Year Rules
The calculator correctly handles leap years. A year is a leap year if it is divisible by 4, except for century years which must also be divisible by 400. So 2000 was a leap year, but 1900 was not. February 29 exists only in leap years, and the calculator handles date arithmetic around these boundaries correctly.