Fertility Friend
Here is a description from their
website:
FertilityFriend.com is the leading internet destination for women trying to conceive. The centerpiece of FertilityFriend.com is a state of the art, easy to use, online fertility charting system. FertilityFriend.com was the first interactive online fertility charting system and remains the leading, most accurate, and most comprehensive charting plan available today. Since pioneering the concept of online fertility charting in 1998, FertilityFriend.com has helped hundreds of thousands of women to achieve pregnancy.
FertilityFriend.com is free but they also offer a VIP version, which you can choose month to month, 3 mo. or a year. A year is only
$45! Like them on Facebook and get discounted memberships! Frequently you can get yearly memberships for around $25 if you look for their specials. You do not have to pay for the site to be able to chart effectively.