Find the day of the week for any date using Zeller's congruence. Enter any year, month, and day to instantly know if it falls on a Monday, Friday, etc.
The Day of Week Calculator determines which day of the week (Monday through Sunday) any date falls on. It uses Zeller's congruence, a well-known mathematical algorithm that computes the day of the week for any Gregorian calendar date without lookup tables or date libraries.
Ever wondered what day of the week you were born? What day Christmas falls on in 2030? Whether a historical event happened on a weekday or weekend? This calculator answers all these questions instantly for any date in the Gregorian calendar.
The algorithm is purely mathematical, working with the year, month, and day as integers. It correctly handles leap years, century boundaries, and all the quirks of the Gregorian calendar. Whether you enter a date from 1582 (when the Gregorian calendar began) or 3000, the result is accurate.
Integrating this calculation into regular planning habits ensures that work priorities reflect actual data about where time and energy produce the greatest results each week.
Knowing the day of the week for any date is useful for historical research, event planning, scheduling, and personal curiosity. This calculator uses a proven mathematical formula to give instant results for any date—past, present, or future—without relying on calendars or date libraries. Precise quantification supports meaningful goal-setting and accountability, ensuring that improvement efforts are focused on areas with the greatest potential impact on output.
Zeller's Congruence (Gregorian): h = (q + floor(13(m+1)/5) + K + floor(K/4) + floor(J/4) − 2J) mod 7 Where: q = day, m = month (March=3...December=12, Jan=13, Feb=14 of prev year), K = year mod 100, J = floor(year/100). Result: 0 = Saturday, 1 = Sunday, 2 = Monday, ..., 6 = Friday.
Result: Sunday
Applying Zeller's congruence to February 8, 2026: the algorithm computes the day of the week as Sunday. This means February 8, 2026 is a Sunday, which is useful for event planning and scheduling.
Determining the day of the week from a date is a classic problem in calendar mathematics. Several algorithms exist, including Zeller's congruence, the Doomsday algorithm (by John Conway), and the Tomohiko Sakamoto algorithm. All produce identical results but use different computational approaches.
Historians use day-of-week calculations to verify the authenticity of historical documents, as forged documents sometimes contain incorrect day-of-week references. Genealogists use them to verify birth and death records, and researchers use them to contextualize historical events.
An interesting property of the Gregorian calendar is that it repeats exactly every 400 years. This 400-year cycle contains exactly 97 leap years, 4,800 months, and 146,097 days (which is exactly 20,871 weeks). This mathematical elegance makes long-range day-of-week calculations predictable.
Zeller's congruence is a mathematical formula devised by Christian Zeller in the 19th century. It calculates the day of the week for any date in the Gregorian or Julian calendar using simple arithmetic operations on the year, month, and day.
This calculator uses the Gregorian version of Zeller's congruence, which is valid from October 15, 1582 onward. Before that date, the Julian calendar was in use, which has slightly different leap year rules. Results for pre-Gregorian dates may not match historical records.
July 4, 1776 was a Thursday. The signing of the United States Declaration of Independence took place on a Thursday, a fact that can be verified with this calculator or any historical reference.
Yes, enter your birth year, month, and day to find out what day of the week you were born. You can also check future birthdays to see which day they fall on for party planning.
Zeller's congruence is mathematically exact for any date in the Gregorian calendar. There are no approximations or rounding involved. The result is guaranteed to be correct for any valid Gregorian date.
The Gregorian calendar has a 400-year cycle (146,097 days = exactly 20,871 weeks). After 400 years, the day-of-week pattern repeats exactly. This means the year 2400 will have the same calendar as 2000.