I just wanted to share something that i've been using for a year
Every girl needs to know about this app. It's called "period tracker" and should be available on all android phones. It works out when your next period is due by taking the averages of your last 3 periods. It's a bit sketchy in the beginning but surprisingly accurate after a few months.
It also tracks how many days your cycles have been. You can add your moods and symptoms such as backpains, cravings etc. The cutest thing about this app is that you can add the days you have been erm...intimate, and it will show up on the calendar with a little heart. This app also tells you the days that you are most fertile the day of your ovulation. So this app is perfect For those who are looking to conceive, or keep track of feminine body changes. I don't know who invented this app but they sure do deserve a medal.