Pregnancy calendar %?

Nylah • TTC #1 with my husband❤️ We are now pregnant!!!! I`m so incredibly happy!!!
Ladies, just curious. I saw a post that someone did regarding the highest pregnancy % that her calendar projected for her (which was 33%). The highest mine goes up to is 25%. 
Besides age (I'm 36 and can't change that lol) what other factors go into this projection?