NOOOOOOOO!!!! The “Rhythm Method,” also known as the Calendar Method, was developed in the 1930’s and is still used by many people today. There are several variations of the Rhythm Method, ranging from a fixed window of fertility (assuming that days x through y are fertile) to more sophisticated versions that take into account the user’s past cycles. The key difference between the Rhythm Method and Fertility Awareness Based Methods (FABM)? All variations of the Rhythm Method are STATISTICAL in nature, meaning based on dates, or math. True Fertility Awareness Based Methods are OBSERVATIONAL in nature, i.e. based on observation of the body’s signs or symptoms of fertility.
In practical terms, another key difference is that the Rhythm Method is unreliable and can lead to unintended pregnancies, which is why there are so many jokes about it (Catholic Roulette, etc). This is because (a) cycles are not all the same, i.e. your cycles may be very different from your friend’s cycles, and moreover (b) even your own cycles can vary from month to month, and can be affected by factors such as illness, stress, etc. Even for people who have very regular cycles, every cycle is different, and fertility must be assessed on a daily basis.
Unfortunately, FABM are still almost universally confused and conflated with the Rhythm Method, both in academic literature as well as in the popular press. If you tell people that you’re practicing Fertility Awareness, don’t be surprised if the first thing they say has something to do with the Rhythm Method. Take the opportunity to enlighten them!