Ovulation calculation?

Ok so I was trying to calculate my most fertile days because in trying to avoid getting pregnant. Glow says something different than all of these other sites which makes me a little nervous...today I had sex but he didn't cum in me. But we went multiple rounds and all that. With no protection so I'm wondering of I could be worried or not? Glow says my period should be starting Jan 15 if that helps to know. Thank you in advance!