Natural family planning

Natural family planning, or 'fertility awareness', is when you learn to identify small physical changes that tell you when you are entering your fertile period each month, and therefore the days when you could become pregnant if you have unprotected sex.

Using natural family planning means that you need to measure these changes carefully at the same time every day and abstain from sex or use condoms at the time when you are fertile. Some people may choose to record their fertility information on a chart or use an app.

Natural family planning is not suitable for people with very irregular cycles, people who might find it difficult to record their temperature every day before getting up and/or people whose daily schedules are disrupted by shift work or frequent travel. It may be used by people who prefer not to use hormone-based contraception.

Natural family planning does not prevent sexually transmitted infections (STIs); condoms are the only effective method of protection against STIs.

Evidence on the effectiveness of the natural family planning method is limited. It depends on how many different indicators of fertility you monitor. The use of one indicator alone is associated with a 24% failure rate within one year, but the use of three indicators (e.g. day of menstrual cycle, nature of cervical secretions and body temperature) reduces the failure rate to 0.4%. This means that when two to three fertility indicators are used correctly, natural family planning is 99% effective at preventing pregnancy (although with typical use this is more like 86-92%).

How it works

Natural family planning works because the levels of certain hormones in your body change throughout your menstrual cycle, causing small physical changes as you reach your most fertile period. These changes are called your ‘fertility indicators’. The most reliable indicators are:

  • Thickening the mucus in the neck of the womb, so it is harder for sperm to penetrate the womb and reach an egg
  • The amount and consistency of your cervical secretions
  • Your body temperature on waking
  • The length of your menstrual cycle

By monitoring and recording these indicators, you will get to know when your fertile days are each month.

You’ll need to monitor changes to your body every day – this means keeping a daily record of your waking or ‘basal’ body temperature, as well as changes to your cervical secretions. You will get to expect these changes as you get used to using this method, but if you are not good at keeping records, then this may not be the most effective method of contraception for you.

Once you’ve recorded these indicators, you need to analyse them to work out when you are likely to be fertile.

The Family Planning Association offers comprehensive guidance on the natural family planning method.

Pros and Cons


  • The fertility awareness method doesn't involve taking any hormones or chemicals, or using physical devices.
  • It can be used to plan pregnancy as well as avoid pregnancy.


  • Doesn’t protect against STIs.
  • You need to avoid sex or use another type of contraception (like condoms) if you have sex during fertile times.
  • You must be properly taught the indicators to make sure your contraception method is effective.
  • It can take a few cycles to learn and work out how to predict your fertile days.
  • You need to keep daily records.
  • Some things such as illness or stress can make results difficult to interpret.
  • It demands a high level of commitment from both partners.
  • It can take longer to recognise your fertility indicators if you have an irregular cycle, or have stopped using hormonal contraception.

Learning to read your fertility indicators

Your fertile time lasts for around 8 - 9 days of each menstrual cycle. Ovulation (when an egg is released from your ovaries) lasts for 12 - 48 hours, however, sperm can live inside a woman's body for up to seven days. This means that if you have sex as much as seven days before ovulation you may get pregnant. Fertility awareness is not just about tracking the 2 - 3 most fertile days, but being aware of the full fertile phase.

As you spend more time using this method, you’ll get to know how your fertility indicators change before, during, and after your fertile days.

  • Cervical secretions: the fluid that you can feel in your vagina will feel more dry just after your period; moist, sticky or creamy as you approach your fertile window; and clear and stretchy (like raw egg white) just before ovulation. After ovulation the secretions revert to being thick and sticky again.
  • Your body temperature: hormonal changes also make your body temperature rise slightly during the second phase of your menstrual cycle, after ovulation. The fertile window ends when you've had three consecutive days of higher temperatures, which are higher than all of the previous six days. It is important that you take your temperature first thing in the morning, before you get out of bed, or after you have been resting for at least 3 hours - this is known as your basal or waking body temperature.
  • Your menstrual cycle: if you have a regular cycle, take your shortest cycle length over the last 12 months, then subtract 20 days to find the first fertile day.

Once you start to look out for these changes, it can become very obvious when you are at your most fertile.

You’ll need to use two or more indicators for effective use of the natural family planning method. Using one indicator alone, for example, counting the days in your menstrual cycle, is not accurate enough to monitor your fertile period, so is not reliable as a method of contraception.

You’ll need a good quality, digital centigrade thermometer, and need to remember to take your temperature every day before you get out of bed, and before you eat or drink anything. Small amounts of physical activity, as well as bathing, stress, ill health or drinking alcohol could change your temperature enough to make it an inaccurate indicator of fertility. Your temperature will only rise by about 0.2 degrees centigrade during the second phase of your menstrual cycle so your measurements need to be as accurate as possible.


Natural family planning is not a suitable method of contraception for people with irregular periods.

This method is suited to people who are confident that they can control when they have sex or negotiate effective condom use during their 8 - 9 fertile days. Users of this method must also be able to reliably take their temperature every day before getting out of bed, it is important to be aware that things like travel or viral illnesses can disrupt the measurements and cause incorrect readings.

It can be harder for people to monitor their fertility indicators during times of major hormonal change, for example if they have recently had a baby, stopped breastfeeding, had a miscarriage, stopped another form of hormonal contraception or are experiencing menopause. During this period and for up 6 months afterwards using another form of contraception such as condoms is recommended.


What is ovulation?

Ovulation is when the ovaries release an egg. It is the most fertile time during your cycle, when you are most likely to get pregnant.

Are there any tools to help me record my fertility indicators?

There are several tools that can help you to monitor and map your fertility:

Fertility charts

These give you a place to record and analyse daily changes. Here are two charts you can download for free, the Sexwise natural family planning chart, or the Natural Family Planning Teaching Association’s chart.

Natural family planning apps

There various apps which allow you to quickly and easily record and track physical and emotional changes. These apps use different methods of tracking your fertility – so make sure you do your research before choosing one that is right for you and your situation.

Many of these apps are free but may charge for additional services, for example, a specialist thermometer that can relay your basal body temperature directly to the app.

Fertility or contraception monitors

These are physical devices which measure the amount of the hormones estrogen and progesterone in your urine. These are available to buy in most high street pharmacies, but can be quite expensive as a regular method of contraception.

Why do cervical secretions change throughout the cycle?

Throughout each cycle the amount of the hormones estrogen and progesterone that your body produces changes, and this affects the feel, quantity and appearance of your cervical secretions.