Nelson Barringer

In celebration of this day that holds so much superstition here are some stat facts about Friday the 13th.

• Every year has at least one Friday the 13th. A year can have up to three occurrences. This creates an average of it occurring 1.72 times per year.
• Friday is the most common weekday for the 13th to land on. This happens because of how leap years shift the calendar over the 400-year cycle of the Gregorian calendar.
• September is the most common month for Friday the 13th over the 400-year cycle.
• Friday the 13th can occur in any month, however certain patterns are common; 1. If a month starts on a Sunday it will have a Friday the 13th. 2, In non-leap years February, March, and November often product them. 3. In leap years January, April, and July normally have them.
• In a 1993 BMJ study, researchers found that fewer people drove on Friday the 13th. However, hospital admissions increased due to accidents compared to other days.
• If today was a random date the probability its Friday the 13th is 0.47% (roughly 1 out of every 212 days)
• The maximum gap between two Friday the 13ths is 426 days. the smallest gap is 28 days.
• There is nothing mathematically unusual about the 13 itself. Across the calendar, every date from 1 to 31 appears exactly the same number of times in the long run. What varies is the weekday pairing.

Overall it’s just a fun day that is whatever you make of it. If you want to geek out with some python here is a script that generates every Friday the 13th in history:

from datetime import date, timedelta
def generate_friday_13ths(start_year: int = 1, end_year: int = 9999):
    """
    - Uses Python's proleptic Gregorian calendar.
    - In Python's datetime module:
        Monday = 0
        Tuesday = 1
        Wednesday = 2
        Thursday = 3
        Friday = 4
        Saturday = 5
        Sunday = 6
    """
    friday_13ths = []
    for year in range(start_year, end_year + 1):
        for month in range(1, 13):
            d = date(year, month, 13)
            if d.weekday() == 4:  # Friday
                friday_13ths.append(d)
    return friday_13ths
def print_friday_13ths(start_year: int = 1, end_year: int = 9999):
    dates = generate_friday_13ths(start_year, end_year)
    print(f"Friday the 13ths from {start_year} to {end_year}:")
    print(f"Total found: {len(dates)}")
    print("-" * 40)
    for d in dates:
        print(d.isoformat())
if __name__ == "__main__":
    # every Friday the 13th in Pythons supported date range
    print_friday_13ths(1, 9999)
    # to make the range smaller
    # print_friday_13ths(1900, 2100)

/end trans