Best Period Tracker?

Hi All! I've been using Flo for the last couple of years to track/predict my cycle and I'm noticing that it doesn't accurately track my period. I thought my period was late every third month by a week and now, looking at trends, I'm noticing flo just doesn't accurately predict it! It's off every third month. Ladies, thoughts? I hate switching over and switching my cycle records over manually so I need advice!

Thank you!!!