Fertility: When Are You Most Fertile?

Become Your Own Ovulation Predictor

Question: When It comes to fertility, when are my most fertile days? Can I become my own ovulation predictor?

We all know from our sex education classes that to become pregnant, a sperm must meet and fertilize an egg.

Timing becomes the greatest issue because an egg is available to be fertilized for only about a 12 to 24 hour period each month—basically, right as or after you have ovulated. This is the time of your most fertile days: the days that you are most likely to get pregnant if you have unprotected sex.

Once you can become your own ovulation predictor, you can have a better sense of your fertility and figure out when your most fertile days are. If you are you don't wish to become pregnant (and are determining your most fertile days as a form of contraception), these are the days that you need to be most careful.

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Answer: Over time, you can track your fertility. Once you can predict ovulation, you should easily be able to determine when you are most fertile.

Understanding Your Most Fertile Days

Also known as your fertile period, there are about seven days during your menstrual cycle when it is actually possible to get pregnant. These are considered to be your most fertile days.

Technically, your fertility is highest during the five days before you ovulate, the day you ovulate (and maybe a day after that), depending on the time that you ovulate.

There are six days that count as your most fertile days because sperm can live up to 5 days. Once released, your egg can only live for about 24 hours. If you have sexual intercourse during this fertile time, By learning to be your own ovulation predictor, you should be able to identify your most fertile days.

How Do I Figure Out My Fertile Days?

Generally speaking, most women ovulate two weeks before the start of their next period. There are many natural family planning techniques to help you determine when you ovulate. If you don't use these, then you can look at the day that your next period begins and count back 14 days (2 weeks). This should give you the day that you ovulated.

In a perfect 28 day cycle, after counting back, you can predict ovulation on Day 14 of your cycle. But beware, don't fall into the trap of believing that you ovulate on Day 14 of your cycle. This is only the case if you have reliable, 28-day cycles.

The Importance of Ovulation Predictors

The whole idea of determining when your most fertile days rests on the notion that you can accurately predict your ovulation. So the very first step in understanding your fertility is knowing when you ovulate.

Becoming a good ovulation predictor means relying on your own fertility awareness and the ovulation signs your body shows you each month. Fertility iPhone apps are actually really good at helping you to chart your fertility to determine when your most fertile days may be occur.

Difficulty Pinpointing Your Fertile Days

Timing your ovulation can become tricky since it may not happen on the same day or same time every month. The length of your cycle may change from month to month as well.

To start with, you will need to do some careful record keeping over a period of at least 3 to 6 months to have a more accurate idea of when you ovulate.

Even if you have charted your cycles for a few months and are fairly confident in the job of being your ovulation predictor, your ovulation may come earlier or later than predicted. This is because ovulation can be thrown off if you:

  • Are sick.
  • Have a specific illness like diabetes or thyroid disorder.
  • Are feeling stressed.
  • Have an imbalance in your hormones or irregular cycles.
  • Are taking certain medications (certain pain medications, antibiotics, or antidepressants).
  • Are having a disruption in your normal routines.
  • Are drinking alcohol or smoking.
  • Are have experienced a 10-15% increase or decrease from a normal level of body fat.

How Knowing Your Fertile Days Helps

Since you can only become pregnant after you have ovulated (released an egg), the goal is to abstain from unprotected sexual intercourse during this time.

Once you know when your most fertile days are, you should not have any unprotected sex during the five days leading up to and including the day that you ovulate, and during the one day (24 hours) after ovulation.

Why five days + one? Sperm can live inside the female body for up to 5 days, so... let's say "Jennifer" ovulates on Day 12. If Jennifer has sex on Day 7, Day 8, Day 9, Day, 10, or Day 11, there can still be sperm living inside of her. So when her egg is released on Day 12, there can be plenty of sperm waiting to fertilize it.

Same goes with Jennifer having sex on Day 13 (the day after she ovulates). After she ovulates, her egg is "open for business" for about 24 hours (then it dies). If Jennifer happens to ovulate in the afternoon or evening in Day 12, her egg can still be joined by a sperm during that 24 hour period.

So if she has sex the next afternoon or evening, her egg may still be still "accepting visitors." Abstaining from unprotected sex the entire day after ovulation is also a wise idea.

More on Calculating Your Fertile Days

If you are relying on knowing when you are most fertile to avoid getting pregnant, the process is always the same:

  • You need to determine the how many days each of your monthly cycle lasts.
  • You need to predict the day that you will ovulate (by charting signs in your body and counting back 14 days from the first day of your period).
  • Once you know this day, count backwards 6 days, and abstain from any unprotected sex for these six days (the five days before ovulation and the day that you ovulate).
  • Then, do not have any unprotected sex for the entire day after the day that you ovulated.

That may be easier said than done. This goes back to our earlier discussion about how the length of your cycle may change from month to month.

So this is not a reliable birth control method unless you have been able to predict when you will ovulate and that you have fairly consistent cycles. Calculating your most fertile days is not limited to a perfect 28 day cycle. You can still determine when you are most fertile no matter how long or short your cycles are.

The key, however, is that your cycles are reliably that long. This means that is you have a 35 day cycle, you tend to have a 35 day cycle every month, and you have charted this to make sure.

Generally speaking, most women consistently have cycles that last 26 to 32 days. This means that ovulation is likely to occur between days 12 and 18. When counting the days of a menstrual cycle, you should count the the day that your period starts as Day 1.

Examples of Most Fertile Days

The fertile period is the six days leading up to and including ovulation, and the one day after you ovulate. You are most fertile the three days leading up to and including ovulation.

Here are some examples to help you calculate your most fertile days. Remember, these results will be most accurate if you can reliably predict when you ovulate (by using your body signs—just as a way to confirm that you have predicted the correct ovulation day). So, you have figured out that:

  • You have a shorter cycle—there are 21 days between periods. This means that you will most likely ovulate on Day 7. So, your most fertile days are Day 2, Day 3, Day 4, Day 5, Day 6, Day 7, and Day 8.
  • You have a regular cycle—there are 27 days between periods. This means that you will most likely ovulate on Day 13. So, your most fertile days are Day 8, Day 9, Day 10, Day 11, Day 12, Day 13, and Day 14.
  • You have longer cycle—there are 33 days between periods. This means that you will most likely ovulate on Day 19. So, your most fertile days are Day 14, Day 15, Day 16, Day 17, Day 18, Day 19, and Day 20.

Looking for Some Extra Help?

You may feel more confident if you have some basic charting tools to help you most accurately determine when you ovulate. Besides using fertility apps, here is a list of some helpful items that you can use to best determine your most fertile days.

  • Basal Body Thermometers
  • Cycle Beads
  • Ovulation Tests and Fertility Monitors

Frequently Asked Questions

  • How many days after your period is ovulation?

    Your menstrual cycle starts on the first day of your period and continues up to the first day of your next period. You are most fertile at the time of ovulation, which usually occurs 12 to 14 days before your next period starts.

  • How many days does ovulation last?

    Ovulation, the release of a mature egg (ovum) from the ovary, lasts only one day.

  • How long after ovulation can you get pregnant?

    Although a mature egg is only fertile for up to 48 hours, the opportunity to conceive—known as the fertile period—is around seven days. The fertile period is the time during which the egg is viable (up to two days) plus the time during which sperm can remain viable in the uterus or fallopian tubes (typically up to five days).

  • How soon after ovulation can you start testing?

    Roughly 12 to 14 days after conception, trace levels of human chorionic gonadotrophin (hCG) can be detected in most urine-based home pregnancy tests. If a blood-based pregnancy test is used, hCG may be detected around 11 days after conception.

  • Are there fertility apps that help predict ovulation?

    Yes, there are numerous apps you can download on the Apple App Store or Google Play. One app designed and endorsed by Planned Parenthood is the Spot On Period Tracker. The gender-neutral app is free, secure, and allows you to register online or remain anonymous.

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5 Sources
Verywell Health uses only high-quality sources, including peer-reviewed studies, to support the facts within our articles. Read our editorial process to learn more about how we fact-check and keep our content accurate, reliable, and trustworthy.
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  2. Li D, Heyer L, Jennings VH, Smith CA, Dunson DB. Personalised estimation of a woman’s most fertile daysThe European Journal of Contraception & Reproductive Health Care. 2016;21(4):323-328. doi:10.1080/13625187.2016.1196485

  3. Holesh JE, Bass AN, Lord M. Physiology, ovulation. In: StatPearls [Internet]. Updated May 9, 2021.

  4. Sung S, Abramovitz A. Natural family planning. In: StatPearls [Internet]. Updated June 27, 2020.

  5. American Pregnancy Association. What is hCG? Updated 2021.

Additional Reading
  • Weschler T. (2015). "Taking Charge of Your Fertility: The Definitive Guide to Natural Birth Control, Pregnancy Achievement, and Reproductive Health." New York: HarperCollins.