An Introduction to the Fertility Window and Why It Matters

February 06, 2020

An Introduction to the Fertility Window and Why It Matters

Contrary to what you may have been told, women can’t get pregnant any time of the month! With the 24-48 hour lifespan of the egg and the 5-day lifespan of sperm, we’re only fertile about 5-7 days per cycle! Not only that, but sperm can only stay alive when cervical mucus is present - cervical mucus creates the perfect environment in the vagina for sperm to reach the egg.

The fertile window is the 5-7 days when conception is possible and, for women using FAM to avoid pregnancy, it’s also the time to use a barrier method, abstain, or have alternative sex. If you want to conceive, having sex prior to ovulation on peak day (the last day of the most fertile cervical mucus) is the most ideal time to conceive.

Use a barrier method during the fertile window if you're trying to prevent pregnancy

A side note on cycles, talking about cycles is not the same as talking about months! A cycle is from the first day of full bleeding until the last day before your next period. A cycle is very rarely 28 days, nor do most women ovulate on day 14. Most women will have some variation in their cycle lengths and the general rule of thumb is that a “normal” cycle is anywhere between 24-36 days.

The fertile window may be longer than 5-7 days for some women. This is because we can’t actually predict when ovulation will occur. Identifying the beginning of the fertile window (prior to ovulation) differs depending on what method you choose. Some methods will have a calculation, for example the Doering rule in Sensiplan, which calculates your first fertile day based on your earliest ovulation in the last 12 months.

If you have information on the length of your cycle for the last 12 months this would be considered very helpful to know when your fertile window opens. A method that includes a calculation such as the Doering Rule is most effective but, in general, you will want to watch out for a couple days of dryness after menstruation before more moist cervical mucus. Once you shift from dryness to moisture, you can consider yourself fertile and should use protection until you confirm ovulation.

Groove Fertile Window Fertile Phase


Confirming ovulation relies on a couple key fertility markers coming together that let you know ovulation has happened and you’re safe for unprotected sex if you are avoiding pregnancy. For the sympto-thermal method of fertility awareness, this is based on confirming 3 days of a temperature shift and a 3-day count past peak day.

Temperature shift refers to the consistent raised temperature following ovulation - this occurs because progesterone raises basal body temperature after the egg has been released! Peak day is the last day of fertile mucus.

In our next blog post, we'll cover temperature charting in more depth. If you're impatient, you can also download our free Introduction to Fertility Awareness, a beautifully-designed guide written by seven certified educators (including Nathalie!).

Nathalie Daudet at Fertility Awareness Project

Nathalie Daudet is a social worker and FEMM instructor based in Winnipeg, Canada. She discovered fertility awareness after searching high and low for a non-hormonal method of birth control. After learning the magic of fertility awareness and the gift of body literacy, she decided to pursue formal fertility awareness training and share the knowledge of fertility awareness with women looking for a natural birth control option. Fertility Awareness Project is the hub for Nathalie’s FEMM classes in both group and individual formats, online and in person in Winnipeg. If you love this post and would like to thank Nathalie, shop Tempdrop with Nathalie's unique referral link

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