5
5
0
185
27
3
31
0
1
5
5
0
185
27
3
31
0
1
The Day of Week Calculator tells you exactly which day of the week any calendar date falls on — Sunday through Saturday — for any date between 1900 and 2100. Enter any year, month, and day to instantly find the day name, whether it is a weekend or weekday, and which numbered day of the year it is.
Knowing the day of the week for any date has countless practical applications. Event planners verify that a venue booking falls on a Saturday, not Sunday. HR professionals confirm that an employee's hire anniversary falls on a weekday. Historians research what day of the week pivotal moments occurred. Students verify exam dates and registration deadlines. Legal professionals confirm that a court deadline does not fall on a weekend requiring extension to Monday.
The calculation uses JavaScript's Date object, which implements the Gregorian calendar used universally today. The Gregorian calendar has been in use since October 15, 1582, when it was adopted to correct the drift in the older Julian calendar. For dates before 1582, different conventions apply and this calculator uses the proleptic Gregorian calendar (the Gregorian rules extended backwards), which may differ from historical records that used Julian dates.
Notable historical days of the week include: January 1, 1970 (Unix Epoch) — a Thursday; July 4, 1776 (US Independence Day) — a Thursday; December 25, 2025 — a Thursday (Thursdays are well-represented in history). The Gregorian calendar has a 400-year cycle of 146,097 days, which contains exactly 20,871 weeks. Days of the week distribute almost evenly across this cycle, though the 13th of any month is slightly more likely to fall on a Friday than any other day — the infamous 'Friday the 13th' phenomenon.
For programmers, the Tomohiko Sakamoto algorithm efficiently calculates day of week with a compact formula. The Doomsday algorithm (invented by John Conway) provides a method for mental calculation of any day of the week, anchored on easily remembered 'doomsday' dates like 4/4, 6/6, 8/8, 10/10, and 12/12.
This calculator constructs a UTC date from the inputs and calls getUTCDay() which returns 0 (Sunday) through 6 (Saturday). The Gregorian calendar's day-of-week pattern repeats every 400 years (a 146,097-day cycle that equals exactly 20,871 weeks). Day of year is computed as the number of days elapsed since January 1 of the same year, plus 1.
Day number 0 = Sunday, 1 = Monday, ..., 6 = Saturday. If the result is 0 or 6, the date falls on a weekend. Day of Year ranges from 1 (January 1) to 365 or 366 (December 31 in leap and non-leap years respectively). This tells you how far into the year a given date falls.
Inputs
Results
July 4, 2026 falls on a Saturday — a great day for fireworks celebrations
Inputs
Results
December 25, 2025 is a Thursday — many workers will use vacation days to create a long weekend
Enter the year, month, and day in this calculator — the day of the week is computed instantly. Alternatively, you can use the Doomsday algorithm to calculate it mentally, though that requires memorizing anchor dates.
Over a 400-year Gregorian calendar cycle, Saturday occurs 58 times per 400 years compared to 56-57 for other days, making it very slightly the most common day. The differences are so small they are practically irrelevant.
Due to the structure of the Gregorian 400-year cycle, the 13th of any month falls on Friday 688 times, compared to 685 times for the least common day. It is a real but tiny statistical anomaly — Friday the 13th is slightly more common than Monday the 13th or Sunday the 13th.
January 1, 2000 was a Saturday. The Y2K milestone fell on a weekend, which meant most businesses first experienced the new millennium in live operation on Monday, January 3, 2000.
John Conway's Doomsday algorithm identifies 'anchor days' that always fall on the same weekday in a given year. Key doomsday dates: 4/4, 6/6, 8/8, 10/10, 12/12, last day of February, and 5/9, 9/5, 7/11, 11/7. In 2026, the doomsday is Wednesday.
Easter always falls on a Sunday by definition — it is the first Sunday after the first full moon after the spring equinox (March 21). Use the Easter Date Calculator to find the specific Sunday for any year.
A year has 365 days = 52 complete weeks + 1 extra day. In a regular year, one day appears 53 times and the rest appear 52 times. In a leap year (366 days = 52 weeks + 2 days), two days appear 53 times.
A perpetual calendar is a system for determining the day of the week for any date without relying on a printed calendar. Examples include Doomsday, Tomohiko Sakamoto's algorithm, and Zeller's congruence — all mathematical formulas that compute day of week from date inputs.
Yes. The US, Canada, and most of Latin America start the week on Sunday. Most of Europe, Asia, Africa, and Australia start on Monday. The ISO 8601 international standard defines Monday as the first day of the week.
Enter your birth year, month, and day in this calculator. The result will tell you which day of the week you were born on — many people find this surprising or meaningful.
Roboculator Team
The Roboculator Team explains calculations, planning tools, and practical formulas in clear language for real-life situations.
How helpful was this calculator?
Be the first to rate!
Week Number Calculator
Day of Week & Calendar Calculators
Day of Year Calculator
Day of Week & Calendar Calculators
Calendar Calculator
Day of Week & Calendar Calculators
Leap Year Calculator
Day of Week & Calendar Calculators
Moon Phase Calculator
Day of Week & Calendar Calculators
Sunrise/Sunset Calculator
Day of Week & Calendar Calculators
