What is the Fertile Window?


I always joke with my patients about the myths of ovulation, one of the main ones being - “today is the day, we’ve got to have sex right NOW!” There’s an episode of Friends with Monica and Chandler that comes to mind.

In reality, that’s not really how it works. Many people are surprised to find out that sperm can survive for up to 5 days in the female body during the fertile window. And because fertilization happens within 24 hours of ovulation, the full fertile window is actually 7 days long.

Let’s talk about how to figure out when your fertile window starts and ends.

Determining your Peak Day


When it comes to determining when ovulation happens the only way to be super precise is with ultrasound and blood work, but there are lots of other signals ovulation is happening, and we can typically pinpoint it down to a 24 hour window.

Because we don’t know exactly when it happens, when all signs point to ovulation (cervical fluid, BBT charting, and ovulation tests) we call that your peak day. Once you know your peak day your fertile window is simple to figure out: it starts 5 days before and ends 1 day after.

BBT Charting

If you take your temperature every morning in order to chart your cycle, then your peak day is typically when your temperature shifts from lower temps (around 97F) to higher temps (around 98F).

To learn more: Intro to Basal Body Temperature Charting

Cervical Fluid

Egg white or watery clear discharge is common on or just before your peak day. If you don’t notice much when you wipe after using the restroom, then you can insert a finger into your vagina and check the consistency.

To learn more: Let’s Talk about Cervical Fluid

Ovulation Tests

Sometimes called Ovulation Predictor Kits (OPKs) these test urine for levels of Luteinizing Hormone (LH), which is released from the brain to trigger ovulation. You’re likely to get a positive test (a dark line which matches the control line) on your peak day.

To learn more: Using OPKs to Pinpoint Ovulation

What about irregular cycles?


If you can figure out when you ovulate but it changes every cycle, then your fertile window moves around each cycle too. This can make things tricky whether you’re trying to conceive or you’d like to avoid pregnancy.

For those trying to get pregnant, just assume your fertile window starts early, start timing intercourse early and keep trying regularly until ovulation happens and your fertile window ends. You can time sex as frequently as every 48 hours (to allow sperm to regenerate).

If you’re trying to avoid getting pregnant, then fertility awareness method alone may not be a great option for those with irregular cycles, additional contraceptives are usually recommended.