The question I get asked the most is “when is the best time to have sex to get pregnant?”

The possibility that you can fall pregnant from unprotected sex on any day of a women’s cycle is a myth we seem to be taught from puberty to avoid unwanted pregnancies!

In fact, you can only conceive during something called the ‘fertile window’.

So, what is a fertile window?

In simple terms, it begins when you first seeing cervical mucus and ends after you have ovulated and lasts 6 days on average.1 In reality, it’s a little more complicated, and you need to be able to observe, understand and track your cervical mucus.

Cervical mucus is crucial for fertility as it enables sperm to survive long enough to fertilise the egg. In a healthy cycle, as a woman approaches ovulation, she produces oestrogen which stimulates E-type mucus production.2 It’s this type of mucus that allows sperm to survive through until ovulation and when present, has been found to give the greatest chance of pregnancy.3

Once ovulation has occurred, progesterone production increases and remains high throughout the rest of the cycle. Progesterone stops the production of mucus and ‘plugs’ the cervix with thick, gelatinous mucus, preventing the sperm from passing through.4

So, what do you need to look for?

Firstly, you’ll need to get used to checking your cervical mucus daily and making a note of it. Apps like Clue ( help you record this throughout the month and aim to predict your fertile window. Your mucus can be white, cloudy and creamy in consistency or clear and stretchy like egg white. It’s the latter that is your peak mucus and having sex on these days will optimise your chances of getting pregnant. This is because its produced nearer to ovulation and it is the most sperm-friendly.

When you change from being dry to having mucus that is either creamy or egg-white like, this is the start of your fertile window the key time to have sex every 2 to 3 days.4 Your fertile window ends four days after your last day of peak mucus.

I recommend all my clients read ‘The Fifth Vital Sign: Master your cycles and optimize your fertility’ by Lisa Hendrickson-Jack ( to learn exactly how to optimise your fertility through cycle tracking.

What if I don’t have any mucus?

If you don’t notice any mucus, it could indicate an underlying imbalance in the microbiome, as a group of bacteria call lactobacillus that live in the vagina keep the pH at an acidic level that prevents bacteria and yeast infections.4 For these cases, we recommend the Invivo Female Ecologix vaginal swap test to check for infection so we can tailor recommendations to rebalance bacteria in this area.

What can you do to optimise fertility?

Drinking plenty of water and eating lots of fruit and vegetables with high water content like watermelon, strawberries, cucumber, lettuce, and celery will ensure you stay hydrated and improve the quality of your E-type cervical mucus, meaning the sperm is able to penetrate and get through to the egg for fertilisation, increasing your chances of getting pregnant.5

Finally, you must also be having regular sex throughout the month. Ideally, every three days to empty the sperm storage and keep things fresh.


  1. Dunston, D. et al. (1999) ‘Day-specific probabilities of clinical pregnancy based on two studies with imperfect measures of ovulation’, Human Reproductions, 14(7), pp.1835-1839.
  2. Odeblad, E. (1994) ‘The Discovery of Different Types of Cervical Mucus And the Billings Ovulation Method’, Bulletin of the Ovulation Method Research and Reference Centre of Australia, 21(3), pp.3-35.
  3. Bigelow, J. et al. (2004) ‘Mucus observations in the fertile window: a better predictor of conception than timing of intercourse’, Human Reproduction, 19(4), pp.889-892.
  4. Hendrickson-Jack, Lisa (2019) The Fifth Vital Sign: Master your cycles and optimize your fertility, Fertility Friday Publishing Inc.
  5. Katz, D., Slade, D. and Nakajima, S. (1997) ‘Analysis of pre-ovulatory changes in cervical mucus hydration and sperm penetrability.’, Advances in Contraception, 13, pp.143-151.