Fertility: When Are You Most Likely to Get Pregnant?

How to predict your most fertile days

Pregnancy can only happen when a sperm meets an egg—and timing is key to making sure this meeting happens.

An egg is available for just one 12- to 24-hour period each month. You can become pregnant right as or just after your ovary releases an egg (ovulation).

When you've ovulated, you are at your most fertile. During this time, you are most likely to get pregnant if you have unprotected sex.

Learning to predict your ovulation will give you a better sense of when your most fertile days are. If you don't wish to become pregnant, these are the days you need to be the most careful if you're having sexual intercourse.

This article will help you learn how to predict your ovulation. It also discusses some of the problems you may have when trying to predict fertility.

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Understanding Your Most Fertile Days

There are six to seven days during your menstrual cycle when you can get pregnant. This is known as your fertile period.

You are most fertile during the five days before you ovulate, the day that you ovulate, and possibly a day after you ovulate.

Sperm can live up to five days. Once released, an egg only lives for about 24 hours. This is why there are six to seven days that count as being within your most fertile time.

If you have unprotected sex on those days, you may become pregnant.

How to Predict Ovulation

To figure out your most fertile days each month, you need to know when you'll ovulate. To pinpoint that time, you'll need to rely on body awareness and look for ovulation signs each month.

Most people with ovaries will ovulate two weeks before the start of their next period. 

Natural family planning techniques can help you learn when you ovulate. You can also look at the day that you expect your next period to start and count back 14 days from it. This calculation will give you an idea of when you will ovulate.

If you have a very regular 28-day cycle, ovulation usually happens on day 14. However, if the length of your cycle varies, counting back 14 days won't be a good way to predict when you will ovulate.

That said, you do not need a 28-day cycle to use this method—you just need a regular cycle.

You can still figure out when you are most fertile if your cycle is longer or shorter than 28 days. The key is knowing that your cycles are reliable.

In other words, if you have a 35-day cycle, then you have a 35-day cycle every month.

Tracking Your Cycles

The only way to find out if you have regular cycles is to track them for 3 to 6 months. You can use a notebook or an app to track your periods and get a sense of when you're most likely ovulating.

When counting the days of your cycle, the day your period starts is day 1. Most menstruating people have cycles that last 26 to 32 days. For these people, ovulation is likely to occur between days 12 and 18.

Factors That Affect Ovulation

Timing your ovulation can be tricky because it may not happen on the same day or same time every month. The length of your cycle may also change from month to month.

Even carefully tracking the numbers may not always help you predict ovulation. You may ovulate earlier or later than you predicted.

A change in the day of ovulation can have a number of causes, including:

  • Illness
  • A specific disorder like diabetes or a thyroid disorder
  • Stress
  • An imbalance in your hormones or irregular cycles
  • Taking certain pain medications, antibiotics, or antidepressants
  • A disruption in your normal routine
  • Drinking alcohol or smoking
  • A 10-15% increase or decrease from a normal level of body fat

How To Predict Your Fertile Days

If you do not want to become pregnant, you'll need to abstain from having unprotected sex during your most fertile time.

Once you know when you ovulate, you should avoid having unprotected sex:

  • During the six days leading up to and including the day you ovulate
  • During the one day (or 24 hours after ovulation)

Why Six Days + One?

Sperm can live inside your body for up to five days.

Let's say that you ovulate on day 12 of your cycle. If you have sex on days seven, eight, nine, 10, or 11, there could still be sperm living inside you on those days.

When your egg is released on day 12, there could be sperm available to fertilize it.

If you have sex the day after you ovulate, you may also become pregnant. After you ovulate, an egg survives for about 24 hours. 

If you happen to ovulate in the afternoon or evening on day 12, then the egg could be fertilized in the 24-hour period after.

This is why it's best to avoid having unprotected sex the entire day after you ovulate.

How To Use Fertility Prediction

If you want to use fertility prediction to avoid pregnancy, the process is always the same:

  • Determine how many days each monthly cycle lasts
  • Predict the day of ovulation by charting signs in your body and counting back 14 days from the first day of your period
  • Count back six days from ovulation, and abstain from unprotected sex for these six days (which includes the five days before ovulation and the day you ovulate)
  • Do not have any unprotected sex for the entire day after the day you ovulated

Since your cycle may change from month to month, tracking it is not a reliable birth control method.

Examples of Most Fertile Days

Here are some examples to help you calculate your most fertile days.

  • You have a shorter cycle with 21 days between periods. You will most likely ovulate on day seven. Your most fertile days are day two, day three, day four, day five, day six, day seven, and day eight.
  • You have a regular cycle with 27 days between periods. You will most likely ovulate on day 13. Your most fertile days are day eight, day nine, day 10, day 11, day 12, day 13, and day 14.
  • You have a longer cycle with 33 days between periods. You will most likely ovulate on day 19. Your most fertile days are day 14, day 15, day 16, day 17, day 18, day 19, and day 20.

Remember, these results will be most accurate if you can predict when you ovulate. Use your body signs to help confirm you got the day right.

Tracking Tips and Tools

Basic charting tools can help you most accurately determine when you ovulate. In addition to fertility apps, here are some other tracking tools you might find helpful:

Summary

You can become pregnant during and right after ovulation. Sperm can live in your body for up to five days, and you are most fertile for about seven days during your monthly cycle.

You can predict when you will ovulate by tracking your monthly cycle. Count back 14 days from the first day of your period. If you have a predictable cycle, you can use this method to estimate the day you will ovulate.

You can become pregnant if you have unprotected sex in the six days leading up to and including the day you ovulate, plus the day after. 

Keep in mind that factors like illness, being stressed, and weight loss may cause you to ovulate earlier or later than you predicted.

Smartphone apps, a basal body thermometer, ovulation tests, and other tools can help you keep track of your cycle.

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. If you have regular, 28-day cycles, you will likely ovulate in the middle—about 14 days before your next period starts.

  • How many days does ovulation last?

    Ovulation lasts only one day. However, this is not the only day during your cycle when you could get pregnant. You are also fertile for about five days before you ovulate and the 24 hours or so after you ovulate.

  • How long after ovulation can you get pregnant?

    A mature egg is only fertile for up to 24 hours, but the opportunity to conceive lasts around seven days.

    The fertile period includes the time when the egg is viable plus the five days that sperm can remain viable in the uterus or fallopian tubes.

  • How soon after ovulation can you start pregnancy testing?

    Most home pregnancy tests can pick up trace levels of human chorionic gonadotrophin (hCG) about 12 to 14 days after conception.

    If a blood-based pregnancy test is used, hCG might be detected around 11 days after conception.

  • Are there fertility apps that help predict ovulation?

    There are many apps in the Apple App Store or Google Play store for tracking your cycle. One example is the Spot On Period Tracker, which is designed and endorsed by Planned Parenthood. The gender-neutral app is free, secure, and allows you to register online or stay anonymous.

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4 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.
  1. Wilcox AJ, Dunson D, Baird DD. The timing of the "fertile window" in the menstrual cycle: day specific estimates from a prospective studyBMJ. 2000;321(7271):1259–1262. doi:10.1136/bmj.321.7271.1259

  2. Holesh JE, Bass AN, Lord M. Physiology, ovulation. In: StatPearls [Internet]. Treasure Island, Fla: StatPearls Publishing; 2021.

  3. Sung S, Abramovitz A. Natural family planning. In: StatPearls [Internet]. Treasure Island, Fla: StatPearls Publishing; 2020.

  4. American Pregnancy Association. What is hCG?

Additional Reading
  • Weschler T. Taking charge of your fertility: the definitive guide to natural birth control, pregnancy achievement, and reproductive health." New York, NY: HarperCollins; 2015.