Day of the Week Calculator

Precise chronological calculation is essential for historians, genealogists, and legal professionals who need to verify timestamps across centuries. Determining the specific day of the week for a historical date requires more than a simple lookup; it necessitates an understanding of calendar reforms. The most critical shift occurred during the transition from the Julian to the Gregorian calendar, a change that shifted the calendar by 10 to 13 days depending on the country and year (typically 1582 or 1752).

This utility utilizes Zeller's Congruence to calculate the weekday for any date, handling both standard and leap years with mathematical rigor. Beyond simple identification, understanding the context of a date involves knowing the number of working days leading up to it or identifying cyclical patterns, such as the occurrence of Friday the 13th. Accurate date calculation prevents errors in contract verification, historical reenactment planning, and age verification systems.

The core algorithm relies on Zeller's Congruence. For the Gregorian calendar, the formula is:

Where h is the day of the week (0 = Saturday), q is the day of the month, m is the month (3=March, 14=February), K is the year of the century, and J is the zero-based century.