How to use the Date Calculator
The date calculator adds or subtracts years, months and days from a date, or finds the number of days between two dates.
What you need to enter
- Mode
- Date
- Years
- Months
- Days
- Second date (for "between")
The formula
It moves the calendar date by the amounts you enter and handles month lengths and leap years. The gap between two dates is the difference in days.
Worked example
Using the default values in the calculator:
- Mode: Add to a date
- Date: 2026-10-13
- Years: 0
- Months: 0
- Days: 30
- Second date (for "between"): 2026-10-13
| Result | Thu, 12 Nov 2026 |
| ISO date | 2026-11-12 |
Tips for better results
- Use it for deadlines, due dates and anniversaries.
- Weekday names help plan.
Common mistakes to avoid
- Forgetting leap years.
- Counting the start date twice.
Please note: Results are estimates for general use. For safety-critical work such as electrical or building projects, check with a qualified professional and local codes. See our Disclaimer.