Ive been using period tracker for about 4 years now. It always accurately predicts the start of my me trial cycle. From ovulation to my actually period. I like that you can log and keep track of symptoms, mood changes, weight and temperature. The app can also send you reminders to when your period is coming. A for a free app this works wonderfully well.
Shammystar101 about Period Tracker by GP Apps, v9.5.1