Use this calculator to add or subtract days, weeks, months, or years from any date. You can also calculate the difference between two dates or find business days between dates.
Date Calculator
Choose your calculation type and enter the required information to calculate dates.
Date Formats and Conventions
This calculator uses the ISO 8601 date format (YYYY-MM-DD), which is the international standard for date representation. However, dates are displayed in a more readable format in the results.
Common Date Formats:
- ISO 8601: 2024-03-15 (International standard)
- US Format: March 15, 2024 or 03/15/2024
- European Format: 15 March 2024 or 15/03/2024
- Short Format: Mar 15, 2024
Leap Years: The calculator automatically accounts for leap years (years divisible by 4, except for years divisible by 100 unless also divisible by 400). February has 29 days in leap years.
Month Lengths: Different months have different numbers of days:
- 31 days: January, March, May, July, August, October, December
- 30 days: April, June, September, November
- 28 or 29 days: February (29 in leap years)
Frequently Asked Questions
How accurate is this date calculator?
This calculator is highly accurate and accounts for leap years, varying month lengths, and proper date arithmetic. It uses JavaScript's built-in Date object which handles all calendar calculations correctly according to the Gregorian calendar.
What counts as a business day?
In this calculator, business days are Monday through Friday, excluding weekends (Saturday and Sunday). Note that it does not exclude public holidays, as these vary by country and region. You may need to manually adjust for holidays in your specific location.
How does adding months work when the day doesn't exist in the result month?
When adding months to a date, if the resulting day doesn't exist in the target month (e.g., adding 1 month to January 31 would result in February 31, which doesn't exist), the calculator returns the last day of the target month (February 28 or 29 in this example).
Can I calculate dates in the past?
Yes, you can calculate dates in the past by subtracting days, weeks, months, or years from a date. The calculator works for dates from year 1000 to year 9999.
How do I calculate age using this calculator?
Use the "Date Difference" calculation type. Enter the birth date as the first date and today's date as the second date. Select "Years" as the result unit to calculate age in years.
Why does adding 1 month to January 31 result in February 28/29 instead of March 2 or 3?
This is standard date arithmetic behavior in most systems. When adding months, if the day doesn't exist in the resulting month, it rolls back to the last day of that month. This prevents unexpected date jumps and maintains consistency in monthly calculations.