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Unpacking the Term “Fertility Window”

Delving into what "fertility window" actually means, and how it impacts your life.

March 12, 2021
Macie Gelb

You’ve heard the words thrown around for forever. Since health class as an elementary school student to adult life around all your pregnant (or trying to be) friends. But what does it really mean? Scientifically, what is a fertility window, how can you track yours, why does it matter? We researched, so that you don’t have to. 

A woman's hand holds a pregnancy test that indicates she is pregnant.
A fertile window pertains to the period of ovulation in which you have the highest likelihood of becoming pregnant. 

What is a Fertile Window? 

A fertile window is part of the ovulatory period for women, but it also involves the sperm, and how long the sperm is able to stay fertile in the body before the egg drops down as a result of ovulation. During ovulation, an egg can only survive for a maximum of forty eight hours before contact with sperm in order to be fertilised. While the period of ovulation lasts from five-seven days, your best likelihood at getting pregnant would be to have sex one to two days before the ovulation period starts. The actual ovulation cycle only lasts from 12-48 hours, but because sperm can survive and fertilise in the womb for up to five days, the period becomes longer. Having sex one to two days before ovulation begins allows for the sperm to spend some time in the womb, but not too much so that it has lost it’s fertilising power by the time ovulation begins. 

A pregnant woman stands outside with a smile on her face.
General medical literature agrees that the odds of becoming pregnant are highest one to two days before ovulation begins. 

Fertile Window and Your Odds of Getting Pregnant 

Your odds of becoming pregnant depend entirely on timing. In order to figure out the best time to have sex, you need to be able to track your ovulation. Ovulation can be medically and precisely tracked through an ultrasound or a blood test, but those are only effective tests after the ovulatory period has passed, so they are not entirely helpful. You can buy ovulation test kits from a drugstore or online, and use them to estimate your ovulation. These tests work by measuring the luteinizing hormone present in your urine. This hormone is relevant because a rise in the amount of it in your body signals to an egg that it is time to drop, starting the process of ovulation. 

You urinate on the strip, check your levels, and use those results to determine when you will be within 12-36 hours of ovulation. For most strips, if the test line comes up darker than the control line, that means you are near ovulation. You can also choose to use an app like one of these, or a similar program you find and trust. These apps can help you track your complete cycle, from your period to your ovulation. By inputting the different stages of your cycle, these apps can let you know with fairly good accuracy when you should have sex. 

According to research, your likelihood of getting pregnant can differ dramatically depending on where you are in your cycle. Looking at just the few days before and after ovulation, here is what we know: 

  • Five days before ovulation: 0%-7% chance of conception
  • Four days before ovulation: 8%-17% chance of conception
  • Three days before ovulation: 8%-23% chance of conception
  • Two days before ovulation: 13%-29% chance of conception
  • One day before ovulation: 21%-34% chance of conception
  • Day of ovulation: 8%-33% chance of conception
  • One day after ovulation: 0.8%-11% chance of conception
  • Two days after ovulation: 3%-9% chance of conception

Unpacking the Numbers

Based on the above statistics, it is very obvious that there can be huge variation in the likelihood of becoming pregnant. This is because every single person and cycle is different, so there is a large range of possibilities based on a bunch of different factors at work. You may have also noticed that discouragingly, the lower percentage chance of conception does not raise that much, even, on the highest chance days. This is because actually conceiving is a lot harder than society makes it seem. Difficulty with conception is normal, and you are certainly not alone. 

If planning a time to have sex based on these numbers increases conception anxiety, another good method is to have frequent unprotected sex throughout your cycle. That way, you are surely attempting to conceive on one of the higher likelihood days, without having to worry about tracking and buying tests.  

a man and woman hug each other on a beach.
Just as there are methods to track your ovulation, there are also ways to track when you’re not ovulating.

Knowing You Are Not Ovulating

Sometimes, worrying too much about where you are in your cycle can hinder your mental health and attitude towards conception. It can also make you resent the idea of having sex with your partner, which is not an ideal outcome. Not to mention, if you’re not ovulating, no amount of sex can get you pregnant, so being aware of when you’re not ovulating can save you a lot of time and energy. The number one indicator that ovulation is nonexistent or irregular is absent or sporadic periods. If you’re not getting your period, you’re likely not ovulating. 

Planning conception is a stressful and often difficult process. Tracking your cycle to stay on top of your personal numbers and likelihood of conception can help reduce stress for some people. If you find that it has the opposite effect, then pay no mind to the term fertile window! Your fertile window will occur whether or not you’re aware of it, so as long as you and your partner are having regular, unprotected sex, your chances of getting pregnant remain pretty concrete. If you do have regular sex, or purposefully track your ovulation to have targeted sex, and you don’t conceive after one year, or six months if you’re over 35, you may want to see a doctor about your fertility. Remember, fertility difficulties are highly common! 


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