Oculation Date

Ste

On October 10th, I had my period. I read somewhere that ovulation starts 12-16 days after period. So, I added (10+ 16=26), now 26 being the ‘ovulation day.’ Period cycle is 30-33 days approximately. (It varies between those numbers 30-33 days.) On this app, it says my best ttc would be on the 27th of this month, so I’m confused as how this ovulation timing and dates, numbers really work.