I have been using this app for years. Its very accurate. I love how it lets me know the day before my period comes. Its good to have a summary of when all your periods were. Only reason I didnt give 5 stars is when I was pregnant it didnt really recognize that I was after I put back in my period after birth... other than that, app is great!
Nackelten52 about iPeriod Lite Period Tracker, v3.7