5 Weekends in 1 Month Happens More Often Than Every 823 Years

Before you get too excited about this once-in-a-lifetime event and start telling your family and friends, know this: any such claims are false. Combinations of days like 5 Fridays, 5 Saturdays, and 5 Sundays occur much more often than every 823 years!

The 823 Years Myth

If you have an email or a social media account, chances are that you have come across a viral post that claims an upcoming month has a rare combination of weekdays. Share it, the message states, or beware of some bad luck.

A recent version goes something like this:

January 2021 has 5 Fridays, 5 Saturdays, and 5 Sundays. This happens only once every 823 years. The Chinese call it “silver pockets full” or "money bags."

The email is partially right. January 2021 does have 5 Fridays, 5 Saturdays, and 5 Sundays, and so does January 2844. But this is neither special nor unusual. You won't need to wait for another 823 years to see this weekday combination to occur in the month of January. Just 6 more years, because in 2026, January also has 5 Fridays, 5 Saturdays, and 5 Sundays.

A calendar month that contains 5 Fridays, 5 Saturdays, and 5 Sundays actually occurs nearly every year— January 2021, October 2021, July 2022, and December 2023 all have the same weekday pattern.

First Day of the Month

The weekday combinations these 823-year messages refer to aren't exceptional either. A quick look at a calendar will show that the first 3 weekdays of any 31-day month will be repeated 5 times in that month. So, any month that has 31 days and begins on a Friday will have 5 Fridays, 5 Saturdays, and 5 Sundays. Similarly, any 31-day month that begins on a Tuesday will have 5 Tuesdays, 5 Wednesdays, and 5 Thursdays.

Put it to the test in our calendar

Recurring Monthly Calendars

Ready for some math? Here's a more mathematical reasoning of why the 823-year claim is a myth:

Every year has 7 months with 31 days. Each of these months has at least 3 weekdays that happen 5 times during the month. For example, August 2021 has 5 Sundays, 5 Mondays, and 5 Tuesdays. December 2021 has 5 Wednesdays, 5 Thursdays, and 5 Fridays.

There are 7 different days a month can start. So, on average, the combination of any 3 days occurring 5 times in a calendar month will happen once a year.

In any given year, there are only 6 such combinations of days. This is because 2 months with 31 days start on the same weekday. In a common year, January and October have the same calendar, while in a leap year, January and July look the same.

The Doomsday Rule for calendars

Topics: Calendar, Fun