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Date Calculator
Find the calendar-correct difference between two dates in years, months, and days, or add/subtract a number of days, weeks, months, or years from a date — with proper handling of month-end dates and leap years, not fixed-length month arithmetic.
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Features
- Date difference in years, months, and days, plus total days and weeks
- Add or subtract days, weeks, months, or years from a date
- Calendar-correct month/year arithmetic — no fixed 30-day approximation
- Handles leap years and month-end dates correctly
How to use
- Choose Date difference or Add/subtract.
- For a difference, enter a start and end date.
- For add/subtract, enter a start date, an amount, a unit, and a direction.
- The result updates automatically.
FAQ
- How does adding a month to a month-end date work?
- It clamps to the target month's last valid day rather than overflowing — January 31 plus one month lands on February 28 (or 29 in a leap year), not March 3. The same clamping applies when adding years to a February 29 date in a non-leap target year.
- Why isn't a month treated as a fixed number of days?
- Because it isn't one — months range from 28 to 31 days. Using a fixed 30-day approximation would make "add 1 month" land on the wrong date for most months. This tool does real calendar arithmetic instead.
- What if I enter the end date before the start date in the difference calculator?
- It still works — the difference is shown as a positive span, with a note about which date came first.