How to Use the Date Calculator
Select the calculation mode you need using the tabs, enter your dates or numbers, and the result appears instantly.
- Days Between Dates — Pick a start and end date to see the total number of days, broken down into years, months, days, weeks, weekdays, and weekend days.
- Add / Subtract Days — Enter a start date and a positive number to add days, or a negative number to subtract days. The resulting date and day of the week are shown instantly.
- Business Days — Count only Mon-Fri business days between two dates, or add a set number of business days to a start date to find the resulting date.
How Date Calculations Work
The calculator finds the exact difference between two dates by computing the year, month, and day components separately. It accounts for months having different lengths (28, 29, 30, or 31 days) and correctly handles leap years.
For example, the difference between January 31 and March 1 is calculated as 1 month and 1 day in a non-leap year (29 days in total), or 1 month and 1 day in a leap year (30 days total). The algorithm "borrows" days from the preceding month when the end day is earlier than the start day, just like manual subtraction.
Total days are computed using UTC timestamps to avoid timezone and daylight saving time issues, ensuring the count is always exact regardless of your local time zone.
Business Days Explained
Business days (also called working days) count only Monday through Friday, excluding Saturday and Sunday. This is useful for calculating delivery times, project deadlines, legal notice periods, and other work-related durations.
Note: This calculator does not exclude public holidays, which vary by country, state, and region. If you need holiday-aware calculations, subtract the applicable holidays from the business day count manually.
Common Date Calculations
| Scenario | Mode | Example |
|---|---|---|
| Days until a deadline | Days Between Dates | Today to Dec 31, 2026 |
| Shipping arrival date | Add / Subtract Days | Order date + 5 days |
| 90-day warranty end | Add / Subtract Days | Purchase date + 90 |
| Project working days | Business Days (count) | Start date to end date |
| 2-week notice end date | Business Days (add) | Today + 10 business days |
| Days since an event | Days Between Dates | Event date to today |
| Semester length | Days Between Dates | First day to last day |
| Contract expiry | Add / Subtract Days | Signing date + 365 |