Next Friday the 13th

Why some years have three and some have only one

Every calendar year has at least one Friday the 13th, and can have as many as three, because the 13th of each month cycles through the seven weekdays in a pattern that repeats over a 400-year Gregorian cycle rather than a simple yearly one. Months are also uneven lengths, which shifts which weekday the 13th lands on unevenly rather than in a clean rotation — some stretches of the calendar cluster multiple Friday-the-13ths together, others go many months without one.

Nothing supernatural about the math

This page just checks every 13th of the month going forward from today until it finds one that's a Friday — the same kind of straightforward date arithmetic behind the Nth Weekday of the Month Finder, applied to a fixed day-of-month instead of a fixed occurrence count.