Fertility prediction off?

Sherri • With the help of Glow, now pregnant with my third and final baby! :)
I just ended my period Saturday January the 4th. And I know that most fertility specialists say that you are most fertile approx. 14 days after your cycle. So my question would be if the 14 day rule is true then why does the fertility guide say that my most fertile day is this Thursday the 9th. With a 31% chance of conceiving. And on the 14th. ( just going by the 14-day rule) it says I only have a 2% chance of pregnancy?! I know I had to add days to my period cycle and I'm not sure if that threw off the prediction. Please Help! Thanks in advance! :)