How Effective is the Calendar Method?

Let’s take a look at a type of natural family planning called calendar methods. We’ll cover how the calendar method works as well as its effectiveness. We’ll also look at some other alternative birth control options and why learning your unique ovulation can give you increased knowledge of your own fertility.

Calendar with xs marking off days surrounded by colored sparkles illustrating the calendar method

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 cycle and learn their own fertility. 

Types of calendar methods

There are in fact two types of calendar method: 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 abstain from sex or use protection on days when you’re fertile.

How does the rhythm method work?

In simple terms, the calendar method works by counting cycle days to work out when you’re most likely to be fertile. Before it can be used as a birth control method, you must monitor the length of your cycle for six cycles first. If you have very short cycles then the calendar method may not be a suitable option. 

Once you know your cycle lengths, you can do some manual calculations and work out your fertile days based on the assumption that ovulation happens at the same time in each cycle. Once you’ve done the math and worked out when you’re fertile, it’s up to you and your partner to either abstain from sex on fertile days or use a condom for protection. 

How does the standard days method work?

The standard days method is different to the rhythm method in that there are set days in the cycle when you should assume you are fertile. Users of the standard days method count a 12 day fertile window for those with regular menstrual cycles (26-32 days long). This means abstaining from sex or using another form of birth control from cycle day 8 to 19 of each cycle.

Users of the method typically keep track of their cycle using CycleBeads, 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. There are limited studies on the effectiveness of the rhythm method, but on average fertility awareness based methods such as calendar methods are estimated to be around 85% effective.

Calendar method apps

There are apps out there that work in the same way as 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 a birth control app. 

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 birth control, there’s 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 birth control option. Once inserted into the uterus, they can prevent pregnancy 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, they 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 hormonal birth control containing 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. Natural Cycles is 98% effective with perfect use and 93% effective with typical use. As a regulated medical device, we never sell our users data.

More than a birth control app


We’re more than birth control. Natural Cycles is a fertility journey that gives you the tools to learn more about your body with tailored insights and updates. As well as preventing pregnancy, Natural Cycles can also be used to plan pregnancy if and when you’re ready to start a family. Ready to find out if Natural Cycles could work for you?

Discover the world's first birth control app.

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Written By

Jennifer Gray

A writer with a passion for women’s health, Jennifer Gray has years of experience writing about various reproductive health topics including birth control, planning pregnancy, women’s anatomy, and so much more.

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Scientifically Reviewed

Jack Pearson

With 10 years of experience working in the field of fertility, Jack Pearson is Natural Cycles’ in-house expert. As Medical Affairs Manager, he dedicates his time to conducting groundbreaking research and educating healthcare professionals.

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