How to Find What Day of the Week Any Date Falls On
It sounds like a trivial question until you actually need the answer. What day was I born? Is my anniversary a weekend this year? Will the project deadline fall on a Friday? The calculator above answers all of these instantly.
The Formula: Zeller's Congruence
The classic algorithm for calculating the day of the week is Zeller's Congruence, published by Christian Zeller in 1882. It works for any date in the Gregorian calendar:
Where:
h = day of week (0 = Saturday, 1 = Sunday, 2 = Monday...)
q = day of month
m = month (3 = March ... 14 = February, Jan/Feb use previous year)
K = year of century (year % 100)
J = zero-based century
Modern calculators use JavaScript's Date object which computes days from the Unix epoch (January 1, 1970, Thursday), making the math trivial. The result is identical to Zeller's formula.
What Day of the Week Are Major 2026 Dates?
| Date | Day of Week | Significance |
|---|---|---|
| January 1, 2026 | Thursday | New Year's Day |
| February 14, 2026 | Saturday | Valentine's Day |
| March 17, 2026 | Tuesday | St. Patrick's Day |
| July 4, 2026 | Saturday | US Independence Day |
| October 31, 2026 | Saturday | Halloween |
| December 25, 2026 | Friday | Christmas Day |
| December 31, 2026 | Thursday | New Year's Eve |
Day of the Week Patterns Worth Knowing
The Doomsday Rule
Mathematician John Conway devised a mental math trick called the Doomsday Rule for calculating weekdays in your head. Every year has certain "anchor dates" (called Doomsday) that always fall on the same day of the week within that year. In 2026, the Doomsday is Wednesday — meaning 4/4, 6/6, 8/8, 10/10, 12/12 and a few other anchor dates all fall on Wednesdays.
Weekday Distribution
A standard non-leap year has 365 days = 52 full weeks + 1 day. This means each year starts one day later than the previous. In a leap year (366 days = 52 weeks + 2 days), the shift is two days.
| Year type | January 1 day | Following January 1 |
|---|---|---|
| Regular year (365 days) | Any day X | X + 1 day |
| Leap year (366 days) | Any day X | X + 2 days |
Frequently Asked Questions
What day of the week was I born on?
Enter your birth date in the calculator above. It instantly shows the full day name. For example, if you were born on June 15, 1990, that was a Friday. The calculator also shows what day number it was in the year (day 166) and which ISO week it fell in.
How do I calculate the day of the week without a calculator?
Use the Doomsday Algorithm by John Conway. First, find the "anchor day" for the year. Then use known anchor dates within the year (April 4, June 6, August 8, October 10, December 12 always share the same weekday). Count forward or backward from the nearest anchor date to find any day of the week. It requires practice but works entirely in your head.
What day of the week is the same every year?
No date falls on the same weekday every year because 365 days is not divisible by 7. However, dates repeat their weekday on a 28-year cycle (in non-century years). So 1998 and 2026 have identical calendar structures — January 1 is a Thursday in both years.
Does the Gregorian calendar affect the calculation?
Yes. The calendar reform of 1582 (or later in some countries) dropped 10 days to correct accumulated drift. If you need the weekday for a date before 1582, the Julian calendar applies different leap year rules. Our calculator uses the Gregorian calendar, which is correct for all modern dates.
Why do weeks start on different days in different countries?
In the US and many English-speaking countries, weeks start on Sunday. The ISO 8601 international standard defines Monday as the first day of the week, which is used in most of Europe, Asia, and international business. The calculator shows the ISO week number (Monday-start).