What is the Fertile Window?

Contrary to popular belief, you can’t get pregnant every day of your cycle. There is actually a small number of days when it’s possible to conceive. So, what is the fertile window? Read on to find out when you are most fertile, when’s the best time to get pregnant, and how understanding the fertile window can also prevent pregnancy.

Fertile window represented with a circular illustration of the menstrual cycle, highlighting the pregnancy window

What does fertile mean?

Fertility relates to our ability to be able to reproduce. In short, being fertile means having the ability to conceive, or have children. Women become fertile over a number of fertile days in the menstrual cycle, known as the fertile window, or pregnancy window. Male fertility doesn’t change in the same way as female fertility, but it does decrease over a man’s lifetime and is closely connected to sperm count.

When am I fertile?

The female fertile window is around 6 days long. This includes the day of ovulation and the rate of sperm survival, as sperm can live in the female reproductive system for up to five days before an egg cell is even released! Getting pregnant on your period is unlikely, though not impossible. Because cycle lengths vary from woman to woman, it’s difficult to predict ovulation without knowing your unique cycle. 

The best time to get pregnant in the fertile window

Unlike resilient sperm, the egg cell starts to deteriorate quite quickly after ovulation happens. Within 24 hours the egg cell usually dies, and even before this, as each hour passes, the cell loses quality and conceiving becomes less likely. For this reason and to increase the chances of conceiving, it’s best to have sex the day before ovulation happens.

There are a number of ways to predict ovulation and to plan the best time to get pregnant during the fertile window. Indicators such as a rise in basal body temperature, positive ovulation tests and consistency of cervical mucus can help identify and narrow down the fertile window and help plan a pregnancy

Preventing pregnancy in the fertile window

While finding the fertile window can help identify the best time to get pregnant, this knowledge can also be used to do exactly the reverse: preventing a pregnancy. A short fertile window means there’s only actually six days in a month when a woman can get pregnant.

This means, in theory, that identifying ovulation can be used as birth control if a woman uses protection or abstains from sex during the time when there is a risk of pregnancy. However, ovulation day can vary cycle to cycle and sometimes we don’t know until after it has happened. This is where Natural Cycles comes in. 

How does Natural Cycles calculate the fertile window?

The Natural Cycles app is powered by an algorithm that analyses temperature data (amongst other factors) to predict and identify ovulation. This technology means the app can learn your unique cycle and removes an element of human error involved in traditional fertility awareness-based methods. It’s also completely hormone-free.

The app works in two ways: prevent mode and plan mode so you can tailor it to your reproductive health needs. Natural Cycles provides a daily fertility status and, as birth control, tells you if you need to use protection to prevent pregnancy. Natural Cycles does not protect against STIs.

We hope you’ve enjoyed reading ‘What is the fertile window?’ and have discovered more about your body along the way with us. If you’d like to continue learning more about your unique cycle, why not find out if Natural Cycles could work for you?

Discover Hormone-Free Birth Control

Learn more

4.8

16k ratings in the App Store

Are you ready to learn your unique cycle?

Jen on the roof terrace at Natural Cycles headquarters.

Written By

Jennifer Gray

A writer with a passion for women’s health, Jennifer Gray has years of experience writing about various reproductive health topics including birth control, planning pregnancy, women’s anatomy, and so much more.

Jack in a suit and tie holding a microphone and giving a presentation.

Scientifically Reviewed

Jack Pearson

With 10 years of experience working in the field of fertility, Jack Pearson is Natural Cycles’ in-house expert. As Medical Affairs Manager, he dedicates his time to conducting groundbreaking research and educating healthcare professionals.