< Back to the Blog
Conception

Finding Your Fertile Window: What It Is and How to Calculate Yours

Kylie Han
Kylie Han

If you’re trying to get pregnant (or avoid pregnancy), you need to know your fertile window. Here’s how.

No items found.
Modified On:
Published:
Mar 29, 2024
Est. Read Time:
0
woman on beach running through water
Published:
May 11, 2025
Est. Read Time:
0

If you’re trying to get pregnant (or avoid pregnancy), you need to know your fertile window. Here’s how.

Conception
Share to:

If you’re trying to get pregnant (or avoid pregnancy), you need to know your fertile window. Here’s how.

The fertile window refers to the small period of time in your menstrual cycle in which you are most likely to get pregnant. 

If you're trying to conceive, knowing your fertile window increases your chances of pregnancy during intercourse. And if you're avoiding pregnancy, having sex outside the fertile window significantly reduces your chances of getting pregnant. 

So, how can you figure out what your fertile window is? Here’s your full-proof guide.

Fertile window meaning

Your fertile window is the time in your cycle when you’re likely to get pregnant. This period typically includes the five days before ovulation and 24 hours after you ovulate.

>>MORE: When Am I the Most Fertile?

Essentially, if you want to find your fertile window, it’s crucial to track your ovulation.

Ovulation is one part of your menstrual cycle. Your menstrual cycle begins on the first day of your period and lasts until the first day of your next period. An average menstrual cycle lasts 28 days but can range from 21 to 35 days. 

During your menstrual cycle, your hormones fluctuate. Your uterine lining gets thicker, and your hormones stimulate the growth of follicles in your ovaries to develop a mature egg. Ovulation occurs when one of your ovaries releases the mature egg, usually around day 14 of your cycle. 

The egg then travels through one of your fallopian tubes to your uterus, where it is ready to be fertilized by sperm. If the egg is fertilized by sperm it attaches to your uterine wall, and you become pregnant. If not, hormone levels drop and your uterine lining sheds, resulting in menstruation. 

Even though your egg isn’t fully mature before ovulation, sperm can live in your fallopian tube for up to five days and can fertilize the egg as soon as it’s released. This means that the fertile window is about six days total—starting about five days leading up to ovulation and lasting until the day after. 

Fertile window vs. ovulation

The fertile window isn’t the same as ovulation, but ovulation is a crucial part of the fertile window. Both are crucial time periods if you’re trying to conceive (or avoid conception).

Ovulation is when your ovaries release a mature egg, which sperm can then fertilize. In order to become pregnant, you need a fertilized egg.

The fertile window isn’t just the day of ovulation, but the five days before and the day after. Why? Sperm can live in the fallopian tube for up to five days—which means if you want to conceive, you’ll need to have sex either in the days leading up to ovulation, or while you’re ovulating.

How to find your fertile window

Knowing if and when you ovulate is integral to understanding your fertile window. 

Yet figuring out when you ovulate isn’t always as easy as counting 14 days from your period. Menstrual cycles vary for each person. Ovulation can also change in each cycle, and for those with irregular periods, tracking your fertile window can be even harder and unreliable. 

Tracking your period

Tracking your menstrual cycles in a calendar or period tracking app can help you figure out when you’re ovulating—and therefore find your fertile window—if you have a consistent cycle. 

Tracking physical signs of ovulation

Your body gives off physical signs that you’re ovulating, too. Look out for bodily changes like vaginal mucus, which becomes heavy and slippery during ovulation. You can also record your basal body temperature, or your temperature when your body is at rest—which dips slightly,  then increases 0.5°F after ovulation.

>>MORE: Top 5 Signs of Ovulation: What To Look Out for if You’re Trying To Conceive

Using traditional ovulation predictor kits

Before you ovulate, the amount of luteinizing hormone in your body rapidly increases, which is often referred to as the LH surge. Traditional ovulation predictor kits measure the levels of LH in your body and will say that you’re ovulating if the amount of LH is above a certain threshold.

While this can be a helpful indicator of ovulation, it’s important to note that traditional ovulation predictor kits aren’t accurate for everyone. The “threshold” is simply an average level for an LH surge. For example, if you have low LH levels, the ovulation predictor kit might not pick up on an LH surge even if you’re experiencing one because your levels of LH don’t increase up to the test’s standard. This means you’d get a negative result from the kit—even though you did ovulate.

Tracking your hormones

Tracking your specific hormone levels can be one of the most accurate ways to not only figure out when you’re ovulating, but confirm you have definitely ovulated. 

Digital ovulation predictor kits like Oova can accurately monitor your specific hormone levels to identify your fertile window. Oova measures three hormones—luteinizing hormone, E3G (an estrogen metabolite), and PdG (a progesterone metabolite) —to measure the exact length of your specific cycle and confirm that you’ve ovulated. 

Fertile window: the bottom line

The fertile window is the period of time in your cycle when it’s more likely that you’ll get pregnant. It typically makes up the five days before ovulation and the day following—which means to find your fertile window, you need to track your ovulation.

It’s important to record and gather your own data to understand your ovulation patterns, although stress, lifestyle changes, and ovarian conditions can interfere with some of these body measurements and at-home tests. And while ovulation is crucial to conception, other factors like the viability of sperm and egg can also interfere with fertility and chances of getting pregnant.

Utilizing different methods to monitor ovulation, from recognizing signs of ovulation to tracking your hormones, can be helpful in empowering you to understand and take control of your reproductive health.

About the author

Kylie Han
Kylie Han is a writer from Oakland, California. She's the SEO Manager at The Infatuation, where she loves to support the work of writers and highlight local restaurants. She is also a contributing writer at The Infatuation and is excited to get involved in reproductive health, a passion of hers.

Sources

perimenopause-periods
Should I still see my gynecologist if my periods are just "weird" but not painful?
Yes. Annual visits remain important during perimenopause. Your provider can help determine if your "weird" periods are typical perimenopause changes or something requiring attention. They can also discuss management options to improve your quality of life.
perimenopause-periods
How long do irregular periods last before menopause?
Irregular perimenopause periods typically last 4 to 8 years before your final period, though this varies greatly. Some women experience irregularity for just a few months, while others have irregular periods for over a decade before reaching menopause.
perimenopause-periods
Is it normal to have two periods in one month during perimenopause?
Yes, this can happen, especially in early perimenopause when cycles shorten. You might have a 21 day cycle, meaning you could have a period at the beginning and end of the same calendar month. Track these patterns to distinguish between short cycles and abnormal bleeding.
perimenopause-periods
Why are my periods suddenly so heavy in my 40s?
Heavy perimenopause periods often result from estrogen dominance. When progesterone drops but estrogen remains high, your uterine lining builds up more than usual, causing heavier bleeding when it sheds. This is common in perimenopause but should be evaluated if it affects your daily life.
perimenopause-periods
Can I still get pregnant if my periods are irregular during perimenopause?
Yes. As long as you're having periods, even irregular ones, you may still be ovulating. Pregnancy is possible until you've gone 12 full months without any period. If you don't want to become pregnant, continue using contraception throughout perimenopause.
perimenopause-and-weight-gain
Can you prevent perimenopause weight gain completely?
While you may not prevent all weight changes during perimenopause, you can minimize gain through proactive strategies. Starting strength training before perimenopause, maintaining consistent sleep habits, and managing stress can help your body adapt to hormonal changes more smoothly. Remember, some body changes during this transition are normal and healthy.
perimenopause-and-weight-gain
At what age does perimenopause weight gain typically start?
Perimenopause weight gain can begin in your late 30s or early 40s, often coinciding with the first hormonal changes. Many women notice gradual changes starting 5 to 10 years before their final period. The timing varies greatly based on genetics, lifestyle, and overall health.
perimenopause-and-weight-gain
Does everyone gain the same amount during perimenopause?
No. Perimenopause weight gain varies significantly. Some women gain 5 pounds, others 20 or more, and some maintain their weight. Factors include genetics, starting weight, activity level, stress, sleep quality, and how dramatically hormones fluctuate. Your experience is unique to your body.
Is perimenopause weight gain different from regular aging weight gain?
Yes. While metabolism naturally slows with age, perimenopause weight gain has distinct characteristics. The hormonal shifts cause fat redistribution to the midsection, even if overall weight doesn't change dramatically. This abdominal weight gain pattern is specifically linked to declining estrogen and progesterone, not just aging.
perimenopause-and-weight-gain
Will the weight come off after menopause?
Perimenopause weight gain often stabilizes after menopause when hormones level out, but the weight doesn't automatically disappear. The metabolic and body composition changes that occur during perimenopause tend to persist. However, with consistent healthy habits, weight management becomes more predictable post menopause than during the fluctuating perimenopause years.
https://www.oova.life/blog/progesterone-supplementation-guide
Can I take progesterone if I'm breastfeeding?
Yes, progesterone is generally safe while breastfeeding and doesn't significantly affect milk supply. However, always discuss with your healthcare provider before starting any hormone supplementation while nursing.
https://www.oova.life/blog/progesterone-supplementation-guide
Is it safe to take progesterone throughout pregnancy?
Yes, when prescribed by your healthcare provider. Progesterone supplementation in early pregnancy is safe and can reduce miscarriage risk in women with low progesterone or a history of pregnancy loss. Most providers continue supplementation through the first trimester (weeks 10-12) when the placenta takes over.
https://www.oova.life/blog/progesterone-supplementation-guide
Can progesterone supplementation cause weight gain?
Progesterone can cause temporary water retention and bloating, which may show up as a few pounds on the scale, but it doesn't cause true fat weight gain. Most women don't experience significant weight changes from progesterone supplementation.
https://www.oova.life/blog/progesterone-supplementation-guide
Can I switch from pills to suppositories or vice versa?
Yes, but only under your doctor's guidance. The dosing and timing may need adjustment when switching between forms since they're absorbed differently. Never switch on your own, especially if you're pregnant or undergoing fertility treatment.
https://www.oova.life/blog/progesterone-supplementation-guide
Will progesterone supplementation delay my period?
Yes, progesterone keeps the uterine lining intact, so if you're not pregnant and continue taking progesterone, your period will be delayed. Once you stop taking it, your period should start within 2-10 days. If you are pregnant, progesterone helps maintain the pregnancy and you won't get a period.
https://www.oova.life/blog/progesterone-supplementation-guide
Should I take progesterone pills orally or vaginally?
For fertility and pregnancy support, vaginal progesterone is usually preferred because it delivers higher concentrations directly to the uterus. For perimenopause or general hormone balance, oral progesterone often works well and is more convenient. Your doctor will recommend the best route based on your specific needs.
https://www.oova.life/blog/progesterone-supplementation-guide
When should I start taking progesterone after ovulation?
Typically, progesterone supplementation for luteal phase support starts 2-3 days after ovulation (confirmed by LH surge or temperature rise). Your doctor will give you specific timing based on your protocol. Some women start immediately after a positive ovulation test.
https://www.oova.life/blog/progesterone-supplementation-guide
What's better: progesterone cream or pills?
Pills (oral micronized progesterone) are generally more effective and reliable than creams because absorption from creams is inconsistent. For medical conditions like fertility issues, low progesterone, or HRT, prescription pills or suppositories are strongly recommended over over-the-counter creams.
https://www.oova.life/blog/low-vs-high-progesterone-symptoms
How can I tell if I have low or high progesterone?
The only definitive way to know is through hormone testing via blood tests or at-home urine tests that measure progesterone metabolites. However, symptom patterns can provide clues: anxiety and irregular periods suggest low progesterone, while bloating and extreme fatigue suggest high progesterone.
https://www.oova.life/blog/low-vs-high-progesterone-symptoms
When during my cycle should I test progesterone levels?
Test progesterone levels during the luteal phase, typically 7 days after ovulation or around day 21 of a 28-day cycle. This is when progesterone should be at its peak, making it easier to identify if levels are too low or too high.
https://www.oova.life/blog/low-vs-high-progesterone-symptoms
What are the main differences between low and high progesterone symptoms?
Low progesterone typically causes irregular or heavy periods, anxiety, hot flashes, and sleep issues. High progesterone causes bloating, fatigue, intense breast tenderness, and depression-like mood changes. Low progesterone symptoms persist throughout your cycle, while high progesterone symptoms are most intense during the luteal phase.
https://www.oova.life/blog/low-vs-high-progesterone-symptoms
Can you have symptoms of both low and high progesterone?
Some symptoms like breast tenderness and mood changes can occur with both low and high progesterone, making it confusing. However, the timing, intensity, and accompanying symptoms differ. Hormone testing is the best way to determine which imbalance you're experiencing.
https://www.oova.life/blog/10-dpo
Can stress affect 10 DPO symptoms?
Yes, stress can worsen or mimic 10 DPO symptoms. Stress increases cortisol, which can cause cramping, fatigue, and mood changes similar to both PMS and early pregnancy. During the two-week wait, try stress-reduction techniques like gentle exercise, meditation, or spending time with loved ones.
https://www.oova.life/blog/10-dpo
Is it better to test at 10 DPO or wait?
It's better to wait until 12–14 DPO for more accurate results. Testing at 10 DPO often leads to false negatives because hCG levels may still be too low. If you absolutely can't wait, use a sensitive early detection test with first morning urine, and be prepared to retest in 2–3 days if negative.
https://www.oova.life/blog/10-dpo
What does implantation bleeding look like at 10 DPO?
Implantation bleeding at 10 DPO is typically light pink or brown, much lighter than a period, and lasts 1–2 days. It's often just spotting when you wipe or a few drops on a panty liner. However, only 15–20% of pregnant women experience implantation bleeding—most don't have any bleeding at all.
https://www.oova.life/blog/10-dpo
Why am I cramping at 10 DPO?
Cramping at 10 DPO can be caused by elevated progesterone (whether you're pregnant or not), implantation (if you're pregnant), or premenstrual cramping. Unfortunately, cramping alone can't tell you if you're pregnant since progesterone causes similar symptoms in both scenarios.
https://www.oova.life/blog/10-dpo
What are the chances of a BFP at 10 DPO?
If you're pregnant, you have about a 50–60% chance of getting a positive test at 10 DPO. This means there's a 40–50% chance of a false negative even if you conceived. Chances improve significantly by 12–14 DPO.
https://www.oova.life/blog/10-dpo
What DPO is most accurate for pregnancy testing?
14 DPO (the day of your missed period) is the most accurate time to test, with 99% accuracy. 12 DPO offers 80–90% accuracy. 10 DPO has only 50–60% accuracy. For best results, wait as long as you can—ideally until 12–14 DPO.
https://www.oova.life/blog/10-dpo
Is 10 DPO too early to test?
10 DPO is considered early for pregnancy testing. While some women get positives at 10 DPO, accuracy is only 50–60% if you're pregnant. For best results, wait until 12 DPO (80–90% accuracy) or 14 DPO/missed period (99% accuracy).
https://www.oova.life/blog/10-dpo
Can you have implantation at 10 DPO?
Yes, implantation can still occur at 10 DPO, though 84% of women have already implanted by this point. Late implantation at 10–12 DPO is normal. If implantation happens at 10 DPO, you won't get a positive pregnancy test for another 2–3 days.
https://www.oova.life/blog/10-dpo
What does a negative test at 10 DPO mean?
A negative test at 10 DPO does not mean you're not pregnant. It's very common to get negatives at 10 DPO even if you conceived. Your hCG levels may still be too low, or implantation may have occurred later. Wait until 12–14 DPO to retest for more accurate results.
https://www.oova.life/blog/10-dpo
Can you get a positive pregnancy test at 10 DPO?
Yes, but only about 50–60% of pregnant women will get a positive at 10 DPO. The other 40–50% have hCG levels that are still too low to detect. If you test negative at 10 DPO, wait 2–3 days and test again.
https://www.oova.life/blog/high-progesterone-symptoms
Can high progesterone cause weight gain?
Yes, elevated progesterone can cause temporary weight gain through water retention and bloating. This is a normal part of the luteal phase and early pregnancy.
https://www.oova.life/blog/how-to-increase-estrogen
Does stress affect estrogen levels?
Yes, chronic stress elevates cortisol, which can suppress estrogen production and disrupt hormonal balance. Stress reduction through meditation, yoga, adequate sleep, and self-care practices helps maintain optimal estrogen levels.
https://www.oova.life/blog/how-to-increase-estrogen
When should I consider medical treatment for low estrogen?
Consider medical intervention if natural methods don't improve symptoms after 3 months, if symptoms severely impact quality of life, if you're experiencing early menopause (before 40), or if you have fertility concerns. Hormone replacement therapy may be appropriate in these cases.
https://www.oova.life/blog/how-to-increase-estrogen
What are the signs that my estrogen is increasing?
Signs of rising estrogen include more regular menstrual cycles, reduced hot flashes, improved vaginal lubrication, better mood stability, increased energy, and improved skin elasticity. You may also notice reduced symptoms that originally indicated low estrogen.
https://www.oova.life/blog/how-to-increase-estrogen
Can exercise increase estrogen levels?
Yes, moderate exercise stimulates estrogen release and helps maintain hormonal balance. Aim for 150 minutes of moderate cardio weekly plus strength training twice per week. However, excessive exercise can actually lower estrogen, so balance is key.
https://www.oova.life/blog/how-to-increase-estrogen
How long does it take to increase estrogen naturally?
With consistent dietary and lifestyle changes, you may notice improvements in symptoms within 4-8 weeks. However, significant hormonal changes typically take 2-3 months. Tracking your cycle and symptoms can help you monitor progress.
https://www.oova.life/blog/how-to-increase-estrogen
What foods increase estrogen levels naturally?
Foods high in phytoestrogens can help increase estrogen naturally. The best options include flax seeds (high in lignans), soy products (tofu, tempeh, edamame), lentils, chickpeas, whole grains (oats, quinoa, brown rice), and garlic. These plant compounds mimic estrogen's effects in the body.
https://www.oova.life/blog/perimenopause
What helps relieve hot flashes quickly?
Cool environments, layered clothing, herbal teas, and medical treatments like gabapentin or HRT may help—depending on severity. Lifestyle changes like reducing caffeine and alcohol can also provide relief.
https://www.oova.life/blog/perimenopause
Are there tests to confirm perimenopause?
Yes. Tests measuring estradiol, LH, and FSH levels can indicate hormonal shifts—but diagnosis is often symptom-based since hormone levels fluctuate widely during perimenopause.
https://www.oova.life/blog/perimenopause
How do I know it's perimenopause and not something else?
A doctor may recommend hormone testing (like LH, E3G, and PdG) and track symptom timing. Diagnosis is often based on symptoms combined with age and menstrual pattern changes.
https://www.oova.life/blog/perimenopause
What's the earliest age perimenopause can start?
Some women begin experiencing symptoms as early as their mid-30s, though perimenopause typically starts between ages 38-45.
https://www.oova.life/blog/perimenopause
Does perimenopause affect mental clarity?
Yes. Brain fog and difficulty concentrating are common during hormone fluctuations in perimenopause.
https://www.oova.life/blog/TBD-10-symptoms-and-how-to-get-relief
What happens after the last sign of perimenopause?
After your final period, you enter postmenopause. You'll need 12 consecutive months without a period to confirm menopause. Many symptoms gradually improve, though some like vaginal dryness may persist without treatment.
https://www.oova.life/blog/TBD-10-symptoms-and-how-to-get-relief
When do perimenopause symptoms finally stop?
Some symptoms like brain fog improve after menopause, while others like hot flashes may continue for up to 10 years post-menopause. Vaginal symptoms often persist or worsen without treatment. Each person's timeline is different.
https://www.oova.life/blog/high-progesterone-symptoms
Is high progesterone a sign of pregnancy?
Yes, high progesterone is one of the earliest indicators of pregnancy. Progesterone levels rise significantly after conception to support the developing embryo and reach their peak during the third trimester.
https://www.oova.life/blog/TBD-10-symptoms-and-how-to-get-relief
Can you still get pregnant in late perimenopause?
Yes, you can still get pregnant during perimenopause as long as you're having periods, even if they're infrequent. Continue using birth control until you've gone 12 consecutive months without a period and have officially reached menopause.
https://www.oova.life/blog/TBD-10-symptoms-and-how-to-get-relief
Do symptoms get worse before perimenopause ends?
Yes, most perimenopause symptoms intensify in the final 1-2 years before menopause. Hot flashes peak around your final period, vaginal symptoms worsen, and mood changes increase. However, brain fog typically improves in late perimenopause.
https://www.oova.life/blog/TBD-10-symptoms-and-how-to-get-relief
How long does late perimenopause last?
Late perimenopause typically lasts 1-3 years before your final period. However, the exact duration varies significantly from person to person. You've reached menopause after 12 consecutive months without a period.
https://www.oova.life/blog/high-progesterone-symptoms
What are the symptoms of high progesterone?
High progesterone symptoms include fatigue, bloating, breast tenderness, weight gain, anxiety, depression, headaches, and food cravings. During pregnancy, you may also experience increased nipple sensitivity and muscle aches.
https://www.oova.life/blog/TBD-10-symptoms-and-how-to-get-relief
What are the first signs that perimenopause is ending?
The earliest signs include longer gaps between periods (60+ days), intensifying hot flashes that peak around your final period, and worsening vaginal dryness. These symptoms typically increase in late perimenopause before you reach official menopause.
https://www.oova.life/blog/high-progesterone-symptoms
When should I be concerned about high progesterone?
Consult a healthcare provider if you experience high progesterone symptoms outside your luteal phase when not pregnant, or if symptoms include severe pelvic pain, abnormal vaginal bleeding, or rapid weight gain while on hormone therapy.
https://www.oova.life/blog/high-progesterone-symptoms
How do you test progesterone levels?
Progesterone can be measured through blood tests at your doctor's office or at-home urine tests that measure PdG (a progesterone metabolite). Testing is typically done during the luteal phase, about 7 days after ovulation.

About the Oova Blog:
‍Our content is developed with a commitment to high editorial standards and reliability. We prioritize referencing reputable sources and sharing where our insights come from. The Oova Blog is intended for informational purposes only and is never a substitute for professional medical advice. Always consult a healthcare provider before making any health decisions.

Posts

Latest Articles

Stress and Perimenopause: How It Affects Your Hormones
Perimenopause
Nov 26, 2025

Stress and Perimenopause: How It Affects Your Hormones

Stress makes perimenopause symptoms significantly worse. Learn how stress affects progesterone, cortisol, and estrogen and what you can do about it.

Perimenopause Bloating: Why Your Belly Won't Flatten (And What Actually Works)
Perimenopause
Nov 20, 2025

Perimenopause Bloating: Why Your Belly Won't Flatten (And What Actually Works)

Digestive health symptoms are jaw-droppingly common in perimenopause. Nearly 80% of women report experiencing perimenopause bloating alone. Read on to learn what causes perimenopause bloating (hint: it isn’t you), and what you can do to help ease bloating and discomfort.

Perimenopause Breast Pain: When to Worry and How to Find Relief
Perimenopause
Nov 20, 2025

Perimenopause Breast Pain: When to Worry and How to Find Relief

Pain and soreness in your breasts are common perimenopause symptoms. While breast pain may seem scary, most cases aren’t cause for concern. Here’s what’s behind perimenopause breast pain, when and how to talk to your doctor, and strategies for pain management.