Does the app update your fertile days of your period comes a few days later?

My period is rarely on time. Late by a day or two. Sometimes 4-5 late. Does the app correct the fertile days based on when your period actually started? Last month it predicted fertile days 2.5 weeks after day 1 of period. This month (af is now) it's predicting fertile days to start only a week from day 1 of period. I just wanna make sure I'm taking precautions on the correct days!