Date & Time Calculators
Day of the Week Calculator
Determine the day of the week, week number, and days until a specific date.
What is the Day of the Week Calculator & How does it work?
The Day of the Week Calculator uses Zeller’s Congruence to determine the day of the week for any given date. This formula accounts for leap years and varying month lengths.Additionally, it calculates the week number using the ISO 8601 standard, which defines weeks as starting on Monday and the first week containing at least four days in the new year. The calculator also computes the difference in days between the selected date and today’s date.
h = left(q + leftlfloorfrac{13(m+1)}{5}rightrfloor + K + leftlfloorfrac{K}{4}rightrfloor + leftlfloorfrac{J}{4}rightrfloor – 2Jright) mod 7
h = day of the week (0=Saturday, 1=Sunday, …, 6=Friday)
q = day of the month
m = month (3=March, 4=April, …, 12=December; January and February are treated as months 13 and 14 of the previous year)
K = year of the century (year mod 100)
J = zero-based century (leftlfloorfrac{text{year}}{100}rightrfloor)
q = day of the month
m = month (3=March, 4=April, …, 12=December; January and February are treated as months 13 and 14 of the previous year)
K = year of the century (year mod 100)
J = zero-based century (leftlfloorfrac{text{year}}{100}rightrfloor)
Parameters
Day of the Week
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Week Number of the Year
—
Days Until That Date
—
Frequently Asked Questions
How does the Day of the Week Calculator work?
It uses Zeller’s Congruence to determine the day of the week for a given date, accounting for leap years and varying month lengths.
What is ISO 8601 week number?
The ISO 8601 standard defines weeks starting on Monday, with the first week containing at least four days in the new year.
Can I use this calculator for future dates?
Yes, you can input any date in the past or future to find out the day of the week and other details.
How does the calculator handle leap years?
The formula used by the calculator correctly accounts for leap years when determining the day of the week.
What additional information does the calculator provide besides the day of the week?
It also calculates the ISO 8601 week number and the difference in days between the selected date and today’s date.
Is there a limit to how far back or forward I can go with this calculator?
The calculator supports dates from the year 1583 onwards, which is when the Gregorian calendar was first introduced.
Can I use this calculator for historical events?
Yes, you can input any date from history to find out what day of the week it was and other relevant information.
Results are for informational purposes only and do not constitute professional advice.