How effective is the calendar method?

The need for natural family planning

Birth control methods have changed a lot throughout history. Calendar methods have been used for hundreds of years, as a natural way to prevent pregnancy, but they are less popular now as easier to use, more effective certified methods have entered the playing field. That said, there are still plenty of people who choose to avoid pregnancy in this natural way, whether it’s because of their beliefs or because they want to avoid hormonal contraception.

What is the calendar method?

Calendar methods are a type of natural family planning or hormone-free birth control. These are also known as a fertility awareness-based method (FABM), meaning they require those who follow these methods to monitor their own menstrual cycle and learn their own fertility.

Part of this knowledge about your own reproductive health is understanding that we’re actually only fertile for six days in any menstrual cycle. These fertile days include the day ovulation occurs and the five days prior (since sperm cells can survive in the female reproductive system for up to five days). This period is usually referred to as the fertile window. 

The calendar method relies on users abstaining from unprotected sexual intercourse during the days they’re forecasted to be fertile. That said, the Calendar Method isn’t actually one method but rather an umbrella term for a selection of fertility awareness-based methods. Let’s break these down further to get a closer understanding of how it works!

Types of calendar methods

We’re going to take a look at two types of calendar methods: the Rhythm and the Standard Days method. These differ slightly, but are mainly based on counting calendar days to determine your fertility. You then need to either avoid unprotected sex or use another form of birth control on days when you’re fertile.

What is the Rhythm Method? 

The Rhythm Method is a type of fertility awareness-based method that requires you to monitor your cycle and do some basic math to predict ovulation and your fertile days. Before it can be used as a contraceptive method, you must monitor the length of your cycle for six menstrual cycles first.

How the Rhythm Method works

Since we’re only fertile for a certain time in any cycle, the Rhythm Method is designed to find this fertile time based on counting cycle days, from one menstrual bleed to the start of the next period. 

The calculations work by taking the shortest cycle in the six documented, subtract 18 from the number of days in that cycle and then count from day 1 of the current cycle and mark this day on your calendar. According to the Rhythm Method this will be your first fertile day. 

Once you’ve done the math and worked out when you’re fertile, it’s up to you and your partner to abstain from unprotected sex on fertile days. 

Keep in mind that the Rhythm Method requires your menstrual cycles to be a consistent length and uses math based on a number of historical cycles, meaning if your cycle lengths tend to vary you may not be protected. In fact, the Rhythm Method is not recommended for those who have menstrual cycles shorter than 26 days or for those with irregular menstrual cycles. This is why you must follow it for a six month monitoring period, to get an idea of your shortest cycle, before you can use it. 

To make the Rhythm Method more effective you can combine it with other fertility awareness methods that rely on fertility indicators, such as basal body temperature and cervical mucus methods (this involves monitoring discharge consistency throughout the cycle). Combining these methods into one is known as the symptothermal method. Alternatively, you can let technology do the hard work for you and use the world’s birth control app instead. 

What is the Standard Days Method?

The Standard Days method is an alternative FABM to the Rhythm Method, instead of counting your own cycle, it assumes there are set days when you will be fertile. This means there are no manual calculations to be done, but that this method is even tailored than the Rhythm Method.

How does the Standard Days method work?

Users of this method count a 12 day fertile window for those with regular menstrual cycles (26 days shortest cycle and 32 days longest cycle). This means abstaining from vaginal sex or using other methods of birth control from cycle day 8 to 19 of each cycle.

Users of the method typically keep track of their cycle using Cycle Beads, a string of coloured beads with a rubber ring that moves from bead to bead as the cycle progresses. 

Calendar Method effectiveness

Birth control effectiveness is a difficult thing to compare, as how well a method works can be very individual to the person using it. While there are limited studies into the effectiveness of the Rhythm Method, the broader category of fertility awareness-based methods is shown to have a typical use of 85%. The Standard Days method is 88% effective with typical use and 95% effective with perfect use.

Rhythm Method apps

There are apps out there that work in the same way as these Calendar Methods, but they’ll do the calculations for you. It’s worth noting that not all birth control apps are calendar-based apps, and there are a few key differences you should be aware of if you choose to use an app that bases its science on the Rhythm Method. 

Keep in mind that very few health apps are certified and this can be a useful thing to check before you sign up for one. Free apps may also make their money out of selling your data, so it’s worth checking out their stance on data privacy too.

Some alternative birth control methods

When it comes to contraception, no one-size-fits-all. We believe in contraceptive choice and so we’ve included some hormone-free or low hormonal birth control options and (plus their effectiveness numbers) so you can see what’s on offer alongside the rhythm method. These are just a few additional options, and if you’re considering switching birth control methods we advise that you consult with a medical professional to find the best option for you.

The copper IUD

Intrauterine devices (IUDs) are a type of long-acting contraceptive option. Once inserted into the uterus, they can be used for pregnancy prevention for as long as ten years. The copper IUD doesn’t contain any hormones, but the copper used does create a hostile environment for sperm cells and it also thickens cervical mucus (making it harder for sperm to travel through the female reproductive system). The copper IUD is more than 99% effective with both typical and perfect use. 

The condom

An over-the-counter birth control option, condoms are easy to get hold of and, as well as preventing pregnancy, these barrier methods also protect against sexually transmitted infections. When used perfectly, condoms are 98% effective at preventing pregnancy and with typical use they are 87% effective (this includes user error, including putting a condom on incorrectly, or forgetting to use one at all).

The mini pill

The progestin-only pill (also known as the mini pill) doesn’t contain any synthetic estrogen, only the hormone progesterone. It’s usually recommended for women who can’t take birth control pills containing the hormone estrogen. It works in a similar way to the combined birth control pill, by stopping ovulation, and it’s just as effective (more than 99% with perfect use, and 93% with typical use). 

Natural Cycles

The first birth control app to be FDA cleared, Natural Cycles is a hormone-free birth control method that uses basal body temperature to determine fertility. This means your fertile window is tailored to your unique cycle. Each day you’ll receive a fertility status and predictions of your fertile and non-fertile days. 

On fertile days you should avoid unprotected sex to avoid pregnancy. It doesn’t matter about your shortest or longest cycles, you don’t need to follow a monitoring period, and the method’s effectiveness remains the same. Natural Cycles is 98% effective with perfect use and 93% effective with typical use. Natural Cycles is different to the Rhythm Method, and our study into its accuracy found that using Natural Cycles instead of a Calendar Method reduced the likelihood of getting a wrongly assigned fertile day by 69%.

Learn more

Thanks for reading up on Calendar Methods and some alternative methods! We’re committed to busting stigma and spreading education around women’s health. If you’re still hungry for reproductive health info, why not check out more non-hormonal contraceptive methods, or read up on birth control effectiveness?