AF due???? 16th or 18th???😣😣😣😣😣

Nadiyah

So I have two apps that I use, Glow being one of them and Ovia. Glow says im due for AF on the 16th and Ovia on the 18th of this month. I did not get AF yet but not sure why they have two diffrent dates, even when I put the same information in both. Can someone give me any advice please?