App Help

So my fiancé and I are trying to avoid pregnancy. My periods are super irregular, though (has been anywhere from 16 days to 42 days). However, the app continues to not show my "fertile days" predictor. I find these predictors to be helpful with past apps I've used, but I find this one to be the most accurate with predicting things. Is it not predicting because of my crazy cycles or because I have my status as "avoiding pregnancy?"