Over any given 400-year cycle the 13th day of the month occurs 4800 times. The distribution of 13th day of the month is as follows:

* Monday ( 685 or 14.27% ),
* Tuesday ( 685 or 14.27% ),
* Wednesday ( 687 or 14.31% ),
* Thursday ( 684 or 14.25% ),
* Friday ( 688 or 14.34% ),
* Saturday ( 684 or 14.25% ),
* Sunday ( 687 or 14.31% ).



This means the 13th day of the month is slightly more likely to occur on a Friday.