How does natural family planning work?

Natural family planning works by helping you predict the most fertile time in your cycle. Then you take precautions to avoid pregnancy at that time.

It involves tracking the changes in your body and using this information to work out when you’re going to ovulate and release an egg.

As you’re fertile before and during ovulation, it’s the time when you’re most likely to get pregnant if any sperm enters the uterus or fallopian tubes.

If you know when you’re going to ovulate, you can avoid sex or use barrier methods of contraception. This will be for about 10 days in every cycle.

How to predict when you're ovulating

You can work out when you’re ovulating by tracking:

  • your body temperature

  • changes to your cervical mucus, the fluid produced by your cervix

  • the dates of your period

Research has proven that if you want to be sure when you’re ovulating, you need to track at least 2 of these things.

There are 2 methods of natural family planning that can help you do this:

The symptothermal method

You usually need some training so you can use this method accurately. It involves checking your temperature and charting your cervical mucus and periods.

Many sexual health services will have an expert who can teach natural family planning.

A digital app, for example, Natural Cycles

The only licenced natural family planning app in the UK that we’re aware of is Natural Cycles. You’ll need to pay each month to keep using the app.

This app comes with a thermometer. You record your daily temperature and the dates of your periods on the app. Over time it learns about your cycles and can predict when you ovulate.

Learn more about using these methods.

Understanding how your menstrual cycle works

There are 4 phases to the menstrual cycle


Lasts from the last day of your period until the day you ovulate, which can vary from cycle to cycle. In this phase the egg in the ovary is developing and maturing inside its follicle. This is stimulated by the follicle-stimulating hormone (FSH) in the pituitary gland in your brain.


Usually occurs around 14 days before your next period, but this can vary, you need to check other signs of ovulation. Do not just rely on the days in your cycle. In this phase, the ovary releases the egg, leaving the empty follicle behind. This happens due to a surge of FSH and luteinising hormone (LH), produced by the pituitary gland.


Usually around 14 days. In this phase, the empty follicle produces the hormone progesterone, which stimulates the lining of the womb to thicken. This helps an egg implant if it gets fertilised, which basically means it attaches there ready to get nutrients to develop.


Usually lasts from 3 to 5 days. If the egg is not fertilised, the lining of the womb breaks down and gets released through the vagina, along with the unfertilised egg. If the egg is fertilised, it stays in the womb and there’s no period bleeding.

How your body changes during and after ovulation

Your temperature changes

The empty ovary follicle, left behind when the egg is released, secretes progesterone. This causes a tiny rise in your body temperature. You can measure this with a very accurate thermometer.

When you see this temperature change you’ll know that you’ve ovulated, which means you’re at your most fertile. For the next 3 days, the egg can be fertilised. After that, the chances of getting pregnant are low.

Your cervical mucus changes

The progesterone hormone also reduces the amount of fluid produced by the cervix (cervical mucus) and makes the vagina feel dry.

When your cervical mucus changes from lots of thin, stretchy mucus to almost no mucus at all, you’ll know that you’ve passed your fertile time. You can check this by wiping your vagina with a tissue.