Date Calculator

Date calculations use the JavaScript Date API which correctly handles month lengths, leap years, and daylight saving time transitions. When adding months, if the resulting day exceeds the month length, the date rolls to the next month (e.g., Jan 31 + 1 month = Mar 3 in non-leap years).

Calendar days include all days (weekdays and weekends), while business days typically exclude Saturdays and Sundays (and sometimes holidays). A 30-calendar-day period usually contains about 22 business days. This calculator uses calendar days.

A year is a leap year if it is divisible by 4, EXCEPT years divisible by 100 are NOT leap years, UNLESS they are also divisible by 400. So 2000 was a leap year, 1900 was not, and 2024 is a leap year. Leap years have 366 days instead of 365.

The US uses MM/DD/YYYY, most of Europe and Asia use DD/MM/YYYY, and Japan/China/Korea use YYYY/MM/DD. The international standard ISO 8601 uses YYYY-MM-DD, which avoids ambiguity and is commonly used in computing and data exchange.

ISO 8601 is the international standard for date and time representation. Dates are formatted as YYYY-MM-DD (e.g., 2024-03-15). It eliminates ambiguity between DD/MM and MM/DD formats and ensures dates sort correctly when stored as text.