Ovulation Calculator
Ovulation calculators can quickly estimate the optimal days for conceiving. All you need to know is the first day of your last menstrual period and your average cycle length.
Medically reviewed by Alyssa Dweck, MS, MD, FACOG
When it comes to getting pregnant, it’s all about the timing. Knowing when you're ovulating—and having intercourse on your most fertile days—can increase your chances of conceiving. This is where an ovulation calculator can help.
Like ovulation charts and calendars, an ovulation calculator estimates your fertile days based on the length of your menstrual cycle. The difference is that an ovulation calculator does the math for you, providing information about your fertility within seconds.
Ovulation calculators work best for people with regular menstrual cycles, but those with irregular periods can try them, too. They're even more effective when paired with other fertility prediction methods, such as monitoring your cervical mucus, taking your basal body temperature, or using ovulation predictor kits.
Here, we’ll dive into understanding ovulation calculators, including how they work and how to interpret the results. Then we'll share other tips for optimizing your chances of conceiving.
How Do I Use an Ovulation Calculator?
Using an ovulation calculator is simple and only takes a few short steps. In a nutshell, you put in the date of your last period, along with your average menstrual cycle length, and the calculator estimates your most fertile days. It will also display your predicted ovulation date, guess when your next period might come, and display estimated fertile days in future months.
Once your fertile days are determined, you can time intercourse to maximize your chances of conceiving each month.
How Do Menstrual Cycles Work?
A menstrual cycle is a series of changes that occurs monthly in those with female reproductive organs. Each cycle starts on the first day of menstrual bleeding ("day one") and continues for roughly 28 days, though this length can vary widely. You can only get pregnant by having sex around the time of ovulation, which occurs when a mature egg is released from an ovary.
Most people with a regular menstrual cycle ovulate roughly halfway through it, says Caroline Skahn, CNM, certified nurse midwife with UTHealth Houston. During a typical 28-day cycle, ovulation occurs about 14 days into the cycle.
What if you don't have a 28-day cycle? The general guideline is 14 days before your next period starts, no matter your cycle length, according to the American College of Obstetricians and Gynecologists (ACOG). If your cycle is 35 days long, for instance, you'll probably ovulate on day 21. If your cycle is 24 days, you'll ovulate around day 10.
Estimating ovulation—by using tools like ovulation calculators— can help determine your “fertile window” for any given month, explains Arielle Bayer, MD, an infertility specialist and reproductive endocrinologist at CCRM Fertility of New York. “A ‘fertile window’ is the period of time that is optimal to have intercourse or perform insemination when you are trying to conceive,” she explains.
Related: All About Ovulation Cycles
When Is The Best Time to Conceive?
The best time to conceive is during your fertile window, which spans about six days during each month—the five days before ovulation, plus the day of ovulation itself. "Sperm must be already present and waiting in the reproductive tract for the egg to be released and ovulated. Intercourse must occur before or during ovulation,” says Dr. Bayer.
Indeed, sperm can survive up to five days in the reproductive tract, while an egg lives for about 12 to 24 hours after ovulation. That means days-old sperm can fertilize a newly released egg, which can result in pregnancy.
You should have sex during your fertile window for the best chances of conception. Our ovulation calculator can give you those dates. Note that if reliable methods to predict ovulation are lacking, predicting the fertile window is also unreliable.
Chances of Pregnancy Each Month
Determining your fertile window can increase your chances of pregnancy success, but keep in mind that even when everything goes right, it can take several tries to conceive. According to ACOG, healthy couples in their 20s and early 30s have about a 25% chance of getting pregnant in any given cycle. After the age of 40, your chances of conceiving drop to about 10% per cycle.
Can I Only Get Pregnant During Ovulation?
Yes, you can only get pregnant around the time of ovulation. If you miss your fertile window and your ovulation day, you'll need to wait until the following month before trying to conceive again. No worries—it will be here before you know it!
Related: Can You Only Get Pregnant During Ovulation?
Getting Results from the Ovulation Calculator
If you want to pinpoint your fertility window with an ovulation calculator, it's pretty simple to use. Here are the steps:
First, you'll be prompted to enter the date of your last menstrual period. It’s fine if you aren't sure of the exact date, but the ovulation calculator result might not be accurate if it's off by more than a day or two.
You'll be asked to provide the average length of your menstrual cycle.
After you enter this data, the calculator will give you two pieces of information: the predicted ovulation date and the timeframe when you're most fertile.
So how exactly do you use this information? Well, you have intercourse during those fertile days. But experts recommend that you don’t wait until the end of that fertile period to “do the deed.”
“You should have intercourse in the third, second, or first day before expected ovulation,” suggests Dr. Bayer. “Intercourse on the exact day of ovulation is good, too.” Remember, sperm can live up to five days in your reproductive tract, so it’s a great idea to have sex before the egg releases so that some sperm are ready and waiting.
Many people want to know if it’s necessary to have sex every day when you're trying to conceive, or if spacing it out is better. You should do whatever works for you, but some experts recommend waiting a day or two between intercourse sessions to maximize sperm production.
“The sperm samples are typically better when the male partner has had two to five days of abstinence between ejaculations,” says Dr. Bayer. “So, I tell my patients that sex every other day leading up to ovulation is ideal (and often less pressure)!”
Related: Things to Do Before Getting Pregnant, According to Experts
How Accurate Are Ovulation Calculators?
Ovulation calculators are only estimates. They can’t guarantee accurate information, because menstrual cycle length and ovulation timing can vary, even from month to month.
Still, for certain individuals, ovulation calculators can be quite precise. It's "most accurate for women who have regular cycles,” says Skahn. This means the length of your menstrual cycle is the same each month.
For people with irregular or unpredictable cycles, ovulation calculators may be less likely to pinpoint the exact fertile window, explains Skahn. But they can provide a general guideline for when ovulation is most likely to occur. It’s best to consult with your health care provider for any questions about your specific cycle and fertility.
How Does an Ovulation Calculator Work for Irregular Periods?
If you’ve got a menstrual cycle that's like clockwork, ovulation calculators will likely work well for you, says Jill Purdie, MD, a board-certified OB-GYN and medical director at Pediatrix Medical Group in Atlanta. However, people with irregular cycles “may not be able to use this method because ovulation varies, and that's what makes the cycle irregular,” explains Dr. Purdie.
If you have an irregular cycle, it doesn’t mean that ovulation calculators are totally off the table. Instead, you might need to combine a calculator-based method of determining ovulation with some other methods. We broke down the options below.
Related: How to Schedule Baby-Making Sex With an Ovulation Calendar
Other Ways to Determine Ovulation
There are several other ways to determine ovulation, and you can combine them with an ovulation calculator to maximize your chances of conceiving. Here’s what to know about these methods.
Cervical Mucus Changes
Your cervical mucus looks different throughout your cycle. Around the time of ovulation, it tends to be more abundant, stretchy, clear, and slippery, with an appearance and consistency like raw egg whites. This means that you are likely fertile.
Basal Body Temperature
Measuring and charting your basal body temperature (BBT) can help you conceive, says Dr. Purdie. “With this method, a patient takes their temperature every morning prior to getting out of bed,” she describes. You have to use a special thermometer called a basal body thermometer. Each time you take your temperature, you record it on a chart. You've likely ovulated when you notice an increase of 0.5–1°F.
The BBT method “can help one confirm that they've already ovulated (by the rise in temperature which occurs after ovulation) but will not be helpful to predict when ovulation is about to occur,” says Dr. Bayer. Even so, it can clue you into your cycle, and you can combine this method with other fertility awareness methods.
Ovulation Predictor Kits
Ovulation predictor kits (OPKs) look for the hormone released to trigger ovulation (luteinizing hormone or LH). You will get a positive test result on these kits about 36 hours before you actually ovulate, says Dr. Purdie. “These methods can confirm what the patient is seeing on their calendar as the ovulation date,” she explains. OPKs can be helpful for people with irregular periods looking to better predict ovulation.
Signs of Ovulation
Some people notice signs of ovulation in the body. It might be helpful to record them for a few months so that you can see a pattern and better understand your body's response. You might even use these signs of ovulation, along with ovulation calculators and the other prediction methods described above, to time intercourse when trying to conceive.
The signs and symptoms of ovulation may include:
Mild cramping on one side of the pelvis
Increased, slippery cervical fluid
Heightened sex drive
Mood changes, including increased energy
Breast tenderness
Tips for Getting Pregnant
Dr. Bayer shares other tips for getting pregnant, aside from using methods like an ovulation calculator to determine your fertile days.
Track your menstrual cycles and patterns, especially if this is the first time you're off birth control. If you notice that your cycle lengths are irregular or unpredictable, make an appointment with a health care provider (Also keep in mind that cycles can take a few months to regulate after stopping birth control).
Start taking a prenatal vitamin with folic acid as soon as you start trying to conceive
Eliminate unhealthy habits like smoking, drug use, or excessive alcohol intake.
If you have chronic health issues or take medications regularly, connect with your health care provider before becoming pregnant.
Consider prenatal testing for you and your partner to ensure you're negative for any infections, up to date on vaccines, and aren’t a carrier for any series of genetic mutations.
Related: 7 Steps for Getting Pregnant Faster
Frequently Asked Questions
What is ovulation?
Ovulation happens when an egg is released from one of your ovaries. It typically occurs once during each menstrual cycle.
When does ovulation occur?
Ovulation usually occurs about 2 weeks, or 14 days, before your next period begins. But some people ovulate earlier or later than that.
How soon should you take a pregnancy test after ovulation?
Most health care providers recommend waiting until the day after your expected period to take a pregnancy test. This is usually about two weeks after ovulation.
Are there medical conditions that can affect ovulation?
Medical conditions that can affect ovulation include polycystic ovarian syndrome (PCOS), thyroid issues, hormonal imbalances, primary ovarian insufficiency (POI), and more. Certain lifestyle and environmental factors can also affect ovulation, such as high levels of stress, drug use, and excessive physical activity.
How long should I try to conceive before seeking medical advice?
For people under the age of 35, most providers recommend seeking fertility advice after one year of trying. However, if you're over the age of 35, you should get a fertility workup after six months of trying. Those over 40 should see a fertility specialist before trying to conceive. Many people will seek fertility consultation outside of these parameters, especially due to excess stress about fertility in general.
Can birth control affect ovulation after discontinuation?
Some people start ovulating right away after stopping hormonal birth control, but for others, it can take a few cycles to start ovulating again. Reach out to your health care provider if you have further questions about trying to conceive after stopping birth control.
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