First the Facts

  • There is a possibility of pregnancy when eggs, tubes and sperm are healthy
  • In any one cycle, if all factors are optimal, there is about a 25% chance of a pregnancy occurring
  • Natural Family Planning (NFP) is a method of avoiding (or planning) a pregnancy by learning how to identify the time when you are fertile
  • It involves a person who menstruates monitoring the changes in their body during their menstrual cycle to help them determine when they are most likely to get pregnant and avoiding unprotected sexual intercourse during this time. Or should they wish to get pregnant, have unprotected sexual intercourse during this time.
  • It does not protect against sexually transmitted infections (STIs)
  • NFP is up to 99% effective if used correctly; however, if not used correctly, it will be less effective.
  • There are smartphone apps which support fertility awareness and improve the effectiveness of NFP

What Is the Menstrual Cycle?

  • The menstrual cycle starts on the first day of a period and lasts until the next period starts. The average length of this cycle is 28 days, but it is normal to have cycles which last between 21 and 40 days
  • During a menstrual cycle, the following changes occur:
    • An egg from your ovaries develops and is released (ovulation)
    • During development of the egg destined to ovulate all of the follicles secrete the hormone oestrogen
    • The mucus around the cervix changes, first becoming more abundant (basic fertile mucus), and then after ovulation it becomes thick (basic infertile mucus)
    • The lining of the womb thickens and then after ovulation prepares itself to receive a fertilized egg
    • Once an egg is released, the tissue left behind in the ovary is called the ‘corpus luteum’
    • The corpus luteum secretes two hormones, oestrogen and progesterone
    • The fertile time in a woman’s cycle is short, lasting approximately 24 hours (immediately before ovulation occurs). However, sperm can survive inside a woman’s body for up to seven days, and therefore sex up to seven days before ovulation could potentially result in a pregnancy. This is described as the ‘fertile window’.
    • If the egg is not fertilized during this time, then the lining of the womb will shed, beginning a new period and a new menstrual cycle.
    • For NFP, three things are important – timing of the cycle, cervical mucus changes and body temperature (progesterone causes the body temperature to rise very slightly)

How Does Natural Family Planning Work?

  • NFP depends on you recording the timing of your period, taking your body temperature daily before any other activity and observing changes in your cervical mucus. This will inform (retrospectively) when your body is entering its ‘fertile window’. If a pregnancy is not desired, then unprotected sexual intercourse during this time should be avoided.
  • NFP is effective if used correctly. However, those choosing this method need to be motivated and need to follow the instructions consistently.
  • It is recommended that people intending to use NFP have support (historically this would have been at the local sexual health or genitourinary medicine (GUM) clinic). These days NFP is best supported by widely available apps, which you can download to your smartphone.

Fertility chart and a digital thermometer (Foto:

How Do I Use It?

  • NFP means abstaining from unprotected sexual intercourse during the ‘fertile window’.
  • To use NFP you must monitor your fertility indictors daily. The more indicators you monitor, the more effective NFP will be.
  • There are lots of helpful websites, e.g.

Summary Points

Cervical Mucus

  • As your body prepares for ovulation the amount of mucus produced increases
  • Around ovulation, cervical mucus becomes slippery like egg white – ‘basic fertile mucus’
  • Following ovulation, cervical mucus becomes thicker, preventing the passage of sperm from the vagina into the uterus and out to the distal third of the fallopian tube where fertilization takes place – ‘basic infertile mucus’


  • The most accurate way to monitor temperature is by using a digital oral thermometer to check your temperature every morning before you do anything else, including kissing, eating or drinking!
  • Your fertile window will have ended by the time you start to record a slightly higher body temperature (change of about 0.2 °C)
  • Body temperature can be affected by other things such as having an illness, drinking alcohol, using medication such as aspirin and paracetamol, or taking your temperature at a different time than usual.

Menstrual Cycle

  • This is not a reliable indicator on its own.
  • You should keep a record of your periods and use this to estimate the length of your average cycle, remembering that the first day of the cycle is the first day that you start your period.
  • Ovulation takes place 14 days before the start of a period and tracking your cycle will enable you to predict retrospectively the likely timing of ovulation.

Fertility Apps

  • Fertility apps have been developed to pull together all the data which you record in relation to the timing of your periods, your temperature and your cervical mucus.
  • They are more effective if urine hormone levels are also checked to help identify when ovulation occurs.
  • In motivated users, they have been shown to be as effective as the combined pill at preventing unplanned pregnancy.

Can Breastfeeding Be Used as Natural Family Planning?

In some cases, yes. This is known as the lactational amenorrhoea method (LAM).

  • LAM is an effective contraceptive method if used correctly. For LAM to be effective you must:
  • Be exclusively breastfeeding (not giving your baby any other solid or liquid food) AND
    • Less than 6 months following delivery and not have had a period since delivery
  • If any of these factors do not apply, then an alternative contraceptive method should be considered.

What If I Don’t Use Natural Family Planning Correctly?

  • NFP is only effective if used correctly
  • If you do not use NFP correctly, there is a chance that you could become pregnant
  • If you do not monitor your fertility indicators daily, you should not rely on NFP as a contraceptive method and should use other methods such as condoms or abstain from sex until your next cycle starts.
  • If you have used hormonal contraception or have taken the emergency contraceptive pill, you should use another contraceptive method, such as condoms, until you have completed at least two further menstrual cycles.

Does It Work Straight Away?

No, you should not rely on NFP as a contraceptive method until after 3–6 months of recording your fertility indicators. You should not use hormonal contraceptive methods during this time.

Are There Any Side Effects?

There are no side effects associated with NFP, as it does not use any hormones, chemicals or invasive devices.

Special Considerations

  • NFP can be more challenging to use in certain situations:
    • Your periods are irregular
    • You have recently been pregnant
    • You are breastfeeding
    • You are approaching menopause
  • Being unwell, drinking alcohol, stress, travel, using medications or changes in weight may cause disruptions to your menstrual cycle or fertility indicators, making NFP less effective
  • If you want to have sexual intercourse during your fertile period, other contraceptive methods should be used.
  • The withdrawal method is not effective and is not recommended as a method of contraception (although use may be more common than reported).

Where Can I Get More Information about Natural Family Planning?

You can get it from:

  • A sexual health, GUM or contraception clinic
  • Young person’s clinic
  • Some GP surgeries

Is Natural Family Planning Right for Me?

NFP is not right for everyone. It requires daily monitoring of the cycle, temperature and cervical mucus and an understanding of changes in your body. It is not suitable for people who do not menstruate and may not be suitable if you have a condition that causes irregular vaginal bleeding, e.g. polycystic ovarian syndrome.

There are benefits and risks of using NFP:

AdvantagesDisadvantages / risks
Increasing your fertility awareness can help you avoid and also help you to plan a pregnancyIt takes 3–6 months to learn effectively, and in this time alternative contraception or abstinence is necessary to avoid pregnancy
Suitable for most people who have regular periodsIt is not as effective as long-acting reversible contraceptive choices
There are no chemicals or invasive devices usedIt is dependent on the user
There are no physical side effectsIt involves daily monitoring of temperature and cervical mucus
It can be used by all faiths and culturesStress, illnesses and lifestyle changes can make fertility indicators harder to interpret
It does not protect against STIs
It restricts the number of days when you can have unprotected sexual intercourse without using alternative methods of contraception if there is a desire to avoid pregnancy


Written by: Dr Alice Llambias-Maw, Dr Nikki Kersey and Dr Paula Briggs
Last updated: January 2021

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