When is your fertile window? Everything you need to know

    Updated 19 January 2023 |
    Published 27 September 2019
    Fact Checked
    Medically reviewed by Dr. Barbara Levy, Clinical professor of obstetrics and gynecology, George Washington University School of Medicine and Health Sciences, UCSD Health, California, US
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    Your fertile window is the time you’re most likely to get pregnant. Here, two experts explain what your fertile window is, what happens during ovulation, and what your chances are of getting pregnant at other times. 

    If you’re trying for a baby, it’s likely you’ve wondered when the best time to get pregnant is. It’s possible to conceive at any point in your menstrual cycle if you aren’t using birth control, including during your period. However, there are certain points in the month when you’re most fertile. This is aptly named your fertile window. 

    Your fertile window will differ depending on how long your cycle is and how regular your periods are. It’s sometimes described as your ovulation window. More on that below, but if you’re unsure how to keep track of where you’re at in your cycle, you can use a period tracker like Flo to help with that. 

    Here, two Flo board experts explain what happens during your fertile window, how likely you are to get pregnant throughout your menstrual cycle, and how you can boost your chances of conception. 

    Everything you need to know about getting pregnant

    From when to have sex to early signs of pregnancy

    What is a fertile window and how long is it?

    For many people, their fertile window is around six days long. “Because the egg is viable for 1 to 2 days, and sperm can live in the female genital tract for 4 to 5 days, the fertile window is generally considered to be 6 to 7 days each cycle,” says obstetrician-gynecologist (OB-GYN) Dr. Jenna Flanagan. However, this can be slightly different from person to person. It begins shortly after their period ends — the five days before you ovulate, the day of ovulation (usually around day 14 of your cycle), and the day after you ovulate.

    Your estrogen levels rise throughout your fertile window, and you’ll likely notice changes in your vaginal discharge to reflect this. It becomes slippery and stringy (resembling egg white). “This allows the sperm to travel through the cervix and uterus to the fallopian tubes where they can meet up with the egg. Then, egg fertilization, the first step in pregnancy, can occur,” explains OB-GYN Dr. Jennifer Boyle.

    Your basal body temperature (your temperature when you’re at rest) also typically rises just after ovulation (by around 0.3 C or 0.5 F) and for the latter part of your cycle in the run-up to your next period. This happens because the hormone progesterone is released after ovulation in preparation for conception, so by measuring it, you can track whether you’ve likely ovulated. 

    Flo can help you understand when you’re most likely to get pregnant

    When is your fertile window?

    You may have heard your menstrual cycle talked about in reference to your period. However, your monthly bleed only makes up one part of your cycle. 

    Conveniently, day one of your period marks day one of your menstrual cycle. Your cycle then runs to the start of your next period. On average, this is around 28 days. However, your cycle may be between 21 to 35 days and still be considered normal. 

    The first part of your cycle is called the follicular phase. On average, it lasts between 10 to 16 days but can really depend on your overall cycle length. If you have a 35-day cycle, then the follicular phase is 20 days. Similarly, for a 21-day cycle, the follicular phase is only 7 days. So knowing how long your cycle is can really help. 

    If during your last fertile window you didn’t conceive, then your estrogen and progesterone levels will fall — these are the two hormones that control your cycle. This leads to the lining of your uterus breaking down, and your period will begin. Your period may last between 3 and 8 days. 

    After your period ends, your pituitary gland (a tiny gland in the base of your brain) triggers the release of follicle-stimulating hormone (FSH) to encourage your ovaries to start developing a new egg ahead of your next ovulation window. 

    After a few days (normally around day 14 of your cycle), a surge in luteinizing hormone (LH) triggers an egg to be released from one of your ovaries to travel down your fallopian tubes in order to be fertilized by sperm. This is known as ovulation.  

    Why is your fertile window important?

    Whether you’re trying for a baby or not, knowing when your ovulation window is may help you understand any symptoms you may be experiencing at this point in your cycle (like a change in discharge) and your menstrual cycle as a whole. It also helps you time sex for conception or lets you know when you need to use backup birth control. 

    You can track when you’re ovulating using our online ovulation calculator, by downloading an app like Flo, or using ovulation testing kits. These measure the levels of hormones in your urine to establish if an egg will be released in the next 12 to 36 hours. If you’ve been trying to conceive for a while and haven’t become pregnant, it can be useful to explain to your health care provider how frequently you’re ovulating and how regular your cycle is (if it’s the same length every month).

    Can you get pregnant anytime in your fertile window?

    If you’re trying for a baby, then you’ll likely want to do everything you can in order to conceive. And with conception, timing is often really important. For the highest probability of getting pregnant, research has highlighted that it’s best to have sex in the days just before you ovulate and during ovulation rather than on the days following ovulation. This is because eggs only live for up to 24 hours following ovulation.  

    Approximately 5 days prior to expected ovulation, it’s recommended that you have unprotected sex “every other or every day and then 2 to 3 days after expected ovulation,” advises Flanagan, explaining that this helps “to ensure viable sperm are present when the viable egg is released.” 

    Can you get pregnant outside of your fertile window?

    Whether you’ve only just started to think about having a baby or have been trying to conceive for a while, it’s really important to look after yourself and remember that your well-being is crucial. It’s important not to put pressure on yourself to have sex around this period. While your fertile window is the time you’re most likely to get pregnant, there’s still a chance that you can conceive throughout your cycle if you aren’t using birth control. 

    “The amount of time that sperm can live and be able to fertilize an egg can be as long as five days after sex occurs. If the sperm is there and ready when ovulation occurs, then pregnancy can happen even if the person had sex days before they ovulated,” explains Dr. Boyle.

    Since ovulation dates are usually based on predictions, pregnancy could happen outside the expected fertile window if your actual ovulation occurs earlier or later than estimated.

    “The fertile window can be monitored by various methods including cervical mucus [discharge] tracking, basal body temperature monitoring, and ovulation predictor kits; however, these methods are not exact."

    Your ovulation date can change from cycle to cycle, and there may be some months when you don’t ovulate at all. If you’ve experienced this once or twice throughout a year, this is totally normal and isn’t something you need to worry about. 

    “The fertile window can be monitored by various methods including cervical mucus [discharge] tracking, basal body temperature monitoring, and ovulation predictor kits; however, these methods are not exact,” says Dr. Flanagan. If you’re at all worried that you haven’t ovulated or your cycle has become irregular, you should speak to your health care provider. 

    How to protect yourself if you don’t want to get pregnant

    Knowing when your ovulation window is can be just as helpful if you don’t want to become pregnant. It’s really important to use birth control if you don’t want to conceive; if you aren’t sure what the best option for you is, then your health care provider will be able to talk you through your options — hormonal and non-hormonal. While Flo can help you accurately predict your fertile window, you shouldn’t use this prediction to prevent yourself from getting pregnant. 

    As the day you ovulate can differ from cycle to cycle, it isn’t enough to avoid having penetrative sex on the days when you think you might be in your fertile window. You need to be using birth control too. “Ovulation can be variable, so it isn’t recommended to rely on natural monitoring of ovulation and avoiding vaginal intercourse during that fertile window, as this method of birth control can fail up to 20% of the time,” advises Flanagan.

    Fertile window: The takeaway

    Menstrual cycles can vary in length, meaning your fertile window might be slightly different every month. Tracking your cycle over time can increase your chances of predicting your fertile window accurately

    If you’re trying to get pregnant, then knowing when your fertile window is may help you feel more in control of your family planning by giving you the best idea of when to have sex for conception. Alternatively, if you don’t want to become pregnant, knowing when you’re ovulating and how your hormones change could help you understand any symptoms you experience throughout the month. 

    If you’re ever confused or worried about your menstrual cycle or fertile window, then you should reach out to your health care provider. They will be able to explain any symptoms you’re experiencing and outline how your body changes throughout the month.


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    History of updates

    Current version (19 January 2023)

    Medically reviewed by Dr. Barbara Levy, Clinical professor of obstetrics and gynecology, George Washington University School of Medicine and Health Sciences, UCSD Health, California, US

    Published (27 September 2019)

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