30th Nov -0001

It is important that you are taught natural family planning by a suitably qualified teacher. You can check the availability of instructors in your local area by visiting the Fertility UK website or calling the FPA helpline (0845 112 8690).

The information in this section is designed to serve as an overview only. It is not a substitute for proper instruction and training.

Fertility awareness

The key to natural family planning is to use the signs and symptoms of your body to assess if you’re currently fertile and likely to get pregnant if you have sex.

Three different methods are used in combination to increase the effectiveness of this form of birth control. These are:

  • calculating where you are in your menstrual cycle
  • taking daily readings of your body temperature
  • monitoring changes to your cervix; specifically the secretions of mucus from your cervix

Each method is discussed in more detail below.

Your menstrual cycle

Your menstrual cycle lasts from the first day of your period up to, but not including, the first day of your next period. The length of a woman’s menstrual cycle can vary. Anything from 24 to 35 days is common, although it could be longer or shorter than this. On average, it lasts 28 days.


During your menstrual cycle, hormones are released to stimulate your ovaries. An egg stored in your ovaries begins to grow and mature. When the egg is mature, it’s released from your ovaries (ovulation) and travels down the fallopian tubes.

Occasionally, more than one egg is released.

Ovulation occurs roughly halfway through your menstrual cycle, usually around 10 to 16 days before the start of your next period.

Hormones will also cause the lining of your womb to thicken in order to receive the egg. If the egg isn’t fertilised with sperm, the lining of your womb will break down leading to a period.

An egg can only survive for 24 hours but sperm can survive in your womb for up to seven days, so depending on how soon ovulation followed ejaculation your may be fertile for up to eight days.

When calculating your fertile time, you need to take into account the uncertainty over exactly when you release eggs during your menstrual cycle,.

As the length of a menstrual cycle can vary over time, to ensure your calculations are as precise as possible you will need to measure your menstrual cycle over the course of six months.

One way of doing this is known as the calendar method, which .involves the following steps:

  • record the length of your menstrual cycle every month for six months; this is the number of days from the first day of your period to the first day of your next period; this is usually 28 days but can sometime vary a few days either side
  • take the length of your shortest cycle and the length of your longest cycle
  • subtract 18 days from the length of your shortest cycle – this is the first day of your fertile period
  • subtract 11 days from your longest cycle – this is the last day of your fertile period
  • do not have sex from the first day to the last day of your fertile period

For example if your shortest cycle was 25 days and your longest cycle was 33 days:

  • you would take away 18 from 25 to give you 7 days
  • you would take away 11 from 33 to give you 22 days
  • so you should avoid having sex from day 7 to day 22 of your menstrual cycle

The temperature method

The temperature method is based on the fact that there is a small rise in body temperature after ovulation takes place.

You will need to use either a digital thermometer or a thermometer specifically designed to be used for natural family planning, these are available from pharmacies. Ear or forehead thermometers are not accurate enough to be used in this way.

The temperature method involves:

  • you take your temperature every morning before getting out of bed, this should be done before eating or drinking anything, before smoking and ideally at the same time every morning
  • look out for three days in a row when your temperature is higher than all of the previous six days – the increase in temperature is very small; usually around 0.2C (0.4F) – it is likely that you are no longer fertile at this time

Monitoring your cervix

There is a change in the consistency and amount of the mucus secreted from your cervix during different times in your menstrual cycle.

You can check this by gently placing your middle finger into your vagina and pushing it up to around your middle knuckle.

For the first few days after your period you will probably find that your vagina is dry and you cannot feel any mucus. As the levels of hormones rise to prepare your body for ovulation, you will probably find that your cervix is now producing mucus that is moist and sticky and is white and creamy in colour. This is the start of the fertile period of your menstrual cycle.

Immediately before ovulation the mucus will get wetter, slippery and clearer; much like raw egg white. This is when you are at your most fertile.

The mucus should then soon return to being thicker and sticky and after three days you should no longer be fertile.

Combining methods

There are a number of factors that can disrupt normal fertility signs (see below) so relying on just the one method is not recommended.

It is best to combine the all three methods to give you a more accurate picture of when you are likely to be most fertile.

There are fertility charts that allow you to record information from all three methods which you can then track over the course of each menstrual cycle.

An example of fertility charts and information on how to use them can be found at the Fertility and Education website

There are also a number of apps you can download for smartphones or software for your computer that allow you to track this information.

Things that affect your fertility signs

Your fertility signs can be disrupted if you:

Other factors that affect your body’s natural signs include:

  • altering how and when you take your temperature
  • drinking alcohol
  • taking certain medication
  • being ill

Read more about who may not be suited for natural family planning.

Ovaries are the pair of reproductive organs that produce eggs and sex hormones in females.

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