According to the search results, the maximum number of Friday the 13ths that can occur in a single calendar year is three. This can happen in two ways: either in February, March, and November in a common year starting on Thursday, or in January, April, and July in a leap year starting on Sunday. It is important to note that there is always at least one Friday the 13th per calendar year, but it can be as long as 14 months between two Friday the 13ths.