IS THIS APP CORRECT WITH AF TRACKING?

Daenerys • TTC #1 👶🏽
This is my first time using this app. I always use PD (Period Diary app) to track AF. Just want to know if this app has been accurate with predicting your next flow. 
App I usually use says I'm 3days late. But this app says I'm due tomorrow. 
Let me know if this app has been on point with your cycle