Months that begin on a Sunday will always have a 'Friday the 13th'.
Why Sunday-Starting Months Always Have Friday the 13th
Here's a calendar trick that will stick with you forever: if a month starts on a Sunday, you're guaranteed a Friday the 13th. No exceptions. No escape. The math simply won't allow it.
Think about it. If the 1st falls on Sunday, the 8th is also Sunday. Count five more days and you land on Friday the 13th. Every. Single. Time.
The Inescapable Math
This isn't superstition—it's basic arithmetic. Days of the week repeat every seven days. So if day 1 is Sunday:
- Day 8 is Sunday
- Day 13 is Friday (8 + 5 = 13)
There's no calendar reform, no leap year adjustment, no daylight saving twist that can change this. The relationship between Sunday the 1st and Friday the 13th is locked in place by the structure of our seven-day week.
Friday the 13th: More Common Than You Think
Here's where it gets weirder. The 13th of the month is slightly more likely to fall on a Friday than any other day of the week. Over a 400-year cycle of the Gregorian calendar, the 13th lands on Friday 688 times—more than any other weekday.
The reason involves the complex interplay of leap years, century adjustments, and the 400-year repeat cycle of our calendar. But the bottom line? Friday the 13th isn't rare. It's actually the most common day for the 13th to occur.
How Often Does This Happen?
Every year has at least one month starting on Sunday, which means every year has at least one Friday the 13th. Some years have as many as three. The maximum gap between Friday the 13ths is 14 months, and the minimum is just one month (like February to March in non-leap years when February starts on Sunday).
In 2024, for example, September and December both started on Sunday—giving us two guaranteed Friday the 13ths.
A Party Trick for Life
Next time someone mentions an upcoming month, glance at a calendar. If it starts on Sunday, you can confidently predict a Friday the 13th and watch people's faces as they verify it. It works every time because it has to work every time.
The calendar doesn't care about superstition. It just follows the math. And the math says: Sunday the 1st means Friday the 13th. No luck involved—just cold, reliable arithmetic haunting your calendar.