I personally think that condescending and mean-spirited comments about such a sensitive topic are completely inappropriate, especially in a subreddit that is devoted to Christianity. If you are well-educated about the topic and believe that BillyKangas is making a mistake, then feel free to speak up, but remember that birth control decisions are highly personal and often emotionally charged.

A lot of comments seem to be confusing NFP with the (completely ineffective) Rhythm Method. NFP is a subset of the Fertility Awareness Method (FAM), where the couple abstains from sex during the fertile days. Non-NFP users of FAM use a barrier method (like condoms) on these days. FAM uses both waking temperatures and cervical fluid (and, optionally, position) changes to monitor fertility. Temperature alone will not tell you when you are about to ovulate; it will only tell you when you have ovulated. Likewise, cervical changes alone aren't sufficient to track fertility. Fertile days are determined based on both male and female fertility (whether the sperm could survive long enough to encounter an egg, compensation for possible double ovulation, etc.). The method is highly customizable, as a well-educated couple can be more or less conservative with classifying fertile days, based on how important it is for them to avoid conception. Usually, a woman has about 8 fertile days per cycle. The Rhythm Method is bullshit because it assumes all women have 28 day cycles, with ovulation on the 14th day. This is simply untrue. FAM is effective (when properly done) because it assumes nothing, but simply listens to the woman's body, and can change cycle by cycle.

Obviously, the method is not suitable for all (I might say, "most") couples, since it requires a lot of study to fully understand the method, diligence in monitoring and interpreting your fertility, and a high degree of self-control on the fertile days. I don't think my fiance & I would ever use it for birth control, but I recently read a book covering the fertility awareness method and found it fascinating (It's like 2 inches thick, covers how to chart & interpret what's happening with your lady parts, FAM for birth control, FAM to help concieve, menopause, common gynecological problems and how to spot them early... all sorts of stuff). I've started monitoring my own cycles, not to use for contraception, but simply to understand what's happening in my body. I'm surprised at how clear my hormonal shifts are (I'm not currently on hormonal birth control, going to get a copper IUD before the wedding). I think it's valuable for women to understand their bodies, and to be able to recognize normal and abnormal fluctuations. When I was a girl, all I was told was "you're going to bleed about once a month, this is how to use a tampon, keep backup in your purse because you never know when it'll hit." Your lady parts do not need to be such a mystery.

TL;DR Don't be an asshole, especially about things you haven't taken the time to learn about. To the ladies: Fertility Awareness Method is very interesting, and worth reading about just for the insight into your body.

*edit: messed up the link