When is a Woman Most Fertile?

The period of fertility lasts for around 12 days, but varies between women and from month to month. The most fertile time is around the middle of the menstrual cycle, between day 11 and 16.

Nowadays women delay starting a family to focus on a career, and this means that women are having children much later. Between puberty and around the age of 35 a woman’s fertility  and ability to become pregnant, remains pretty constant. However, after the age of 35, fertility starts to rapidly fall until menopause occurs, which is when the ovaries stop producing an egg and a woman can no longer become pregnant naturally.

However, even in younger and more fertile women, there is actually only a relatively small gap in the month in which a woman can get pregnant. This is why the rhythm method of contraception, when strictly followed, can be effective (although by no means is it ever a full-proof way of avoiding pregnancy).

Of course, many women like to know when is their most fertile period of the month, specifically to avoid intercourse when using physical contraception (such as condoms, coils, cervical caps, contraceptive sponges and diaphragms, all of which are at risk of failure.

If you think that you may be pregnant already, find out How To Tell If You Are Pregnant.

The Menstrual Cycle and Fertility

On average the menstrual cycle is 28 days, although it can be shorter or longer for different women, and it can also fluctuate for individuals. In the diagram above the end of the cycle, days 26 to 32, are grouped to demonstrate that this is the average variation in length.

The menstrual cycle is measured from the first day of bleeding during a period up until the day before the first day of bleeding in the next period.

The first day of the menstrual cycle actually marks the end of the period of fertility, as the period is when an unfertilized egg is released from the body to allow the cycle to start again.

The period is usually around 2 weeks after the egg is produced (or more accurately, released by an ovary), give or take a couple of days. When the egg is released a woman is fertile.

Male sperm can survive for up to 48 hours within the uterus or vagina, so sperm can be present for 2 days before the egg is released, and still “catch” an egg 2 days after it is released. So, assuming that an egg is released on day 14 of your menstrual cycle, intercourse from day 12 to day 16 is most likely to lead to pregnancy. Avoiding sex during this time is the rhythm method of contraception.

When Are You Least Fertile?

Using the above explanation, you can also calculate when you are least fertile from the first day of your period until day 7, so a week after your period starts. If your cycle is very regular then you may not be fertile until day 14, however, there is always a risk of an egg being released earlier.

Due to changes in the timing of the release of eggs and the time sperm can survive, if you are hoping not to get pregnant then it is strongly advisable to avoid intercourse between day 7 and day 20, as this is a “fertile” period.

So, if you are looking to get pregnant focus all your energy on 12-16 days after your period starts, and if you are hoping to avoid pregnancy, stay away from your man during this time!

Further Reading and Advice

• Want a Baby Now? Advice for Getting Pregnant – Women’s Health, accessed 7 Feb 2013.
• Fertility and conception – NHS Choices, accessed 7 Feb 2013.