Finding your fertility window - Mayo Clinic Press (2025)

The Mayo Clinic Guide to Fertility and Conception is the ultimate guide to expanding your family through pregnancy, with clear information and tips for getting pregnant as well as inclusive expertise on options available to all individuals and families. Based on their extensive expertise in helping people build their families, Mayo Clinic physicians break down what contribuites, to healthy eggs and sperm, steps you can take to get ready for pregnancy, how babies are made, and tips for ovulation tracking, timing sex, and improving you chances.

The female body basically runs on a clock, and timing is important. Ovulation typically occurs once a month, and the lone egg that’s produced vanishes about 24 hours after it’s released. That means there’s a fairly narrow window of opportunity for sperm and egg to meet and to successfully mingle. So how do you know when the time is right to try to become pregnant?

A regular menstrual cycle is certainly helpful. But especially if the timing of your period varies, you need a keen eye for detail. The signs and symptoms of ovulation can be subtle. Understanding what symptoms to look for and observing what happens to your own body can help you determine when you’re most likely to be fertile, so that you can plan accordingly.

There are several ways you can keep track of where you are in your menstrual cycle. Beyond an old-fashioned calendar, options include apps, wearable devices and ovulation predictor kits. But along with any of these, the best way to figure out your fertility signs is to observe your body for a while.
After a few months, most people, though not all, are able to uncover patterns in the length of their cycles, the ups and downs of their resting body temperatures, and the changes that occur in mucus coming from the cervix. By following the clues revealed in your personal cycle, you’ll be able to develop a pretty good estimate of when ovulation is likely to occur.

Apps, Devices, and Other Products That Can Help

For some people, identifying patterns in their menstrual cycle is easier said than done. Irregular periods, no real noticeable shifts in body temperature and not being able to detect cervical fluid — or finding cervical fluid all the time — can make it difficult to track changes. This doesn’t mean you can’t conceive; it’s just a little harder to tell when you’re ovulating.

If this sounds like you, don’t worry. Many products and devices, from low-tech to high, are available that can help you track the phases of your menstrual cycle. They can predict when you’re most likely to ovulate and give you clear indications of when your most fertile days are likely to be.

Ovulation Predictor Kits

Over-the-counter ovulation test kits test your urine for the surge in luteinizing hormone (LH) that starts about 36 hours before ovulation. You can buy these kits at almost any pharmacy or online. The cost ranges widely, starting around $15, depending on how many tests come in a kit and any advanced features.

Kits typically contain at least 10 test sticks. Starting on the earliest possible ovulation date — generally day 10 or day 11 for a person whose cycle ranges between 27 and 34 days — test your urine each day to see if LH is present. Hold the stick in your urine stream for a few seconds or place the stick in a urine sample you’ve collected in a sterile container. It’s best to do this the first time you urinate in the morning, as all the hormones your body made overnight are concentrated in your urine. Within a few minutes, an indicator appears on the stick — usually a color change of some sort — telling you whether LH is present or not. Follow the kit instructions carefully to get the best results.

Because the test measures hormone production over a number of hours, it usually detects the middle of an LH surge rather than its very start. Therefore, once the test indicates an LH surge, you know that ovulation will likely occur within the next 24 hours. At this point you can stop testing. This is also the best time to have sex. Most home-based tests are pretty accurate at detecting the LH surge when it occurs. Studies comparing urinary LH tests with ultrasound visualization of ovulation found that LH levels correlated with ultrasound-confirmed ovulation almost every time.

If you ovulate earlier or later than the midpoint in your cycle, it may take a few tries before you find the right time to start testing. Occasionally, ovulation may not occur or a false positive result may happen, telling you LH is present when really it’s not.

Increasingly, some ovulation predictor kits will monitor both estrogen and LH. The estrogen rise can give you a heads-up that LH will peak soon. This can provide more warning of when to expect the LH surge and ovulation — helping to ensure that you won’t miss it.

Fertility Monitors

Another option is to purchase a fertility monitor, a hand-held device that stores daily test results and shows you when your low, high and peak fertility days are. The most accurate monitors rely on urine tests to determine where you are in your cycle.

You start using this monitor on the first day of your period. Each day the monitor advises you whether or not to collect a urine sample right away when you wake up. Once you have a urine sample, you plug the test stick into the monitor. The monitor analyzes the sample and stores the data. In addition to testing for an LH surge, a monitor may test for other hormones — such as estrogen and progesterone — to help detect the fertile window and “learn” the patterns of your cycle. After analyzing the sample, the monitor tells you whether your fertility is low, high or at a peak range.

By using a monitor over several cycles of data, you can get more personalized feedback based on what the monitor learned from your last cycle. As with other products, it’s important to follow the instructions carefully to get the best results.

Evidence suggests that monitors that detect both LH and estrogen offer a fairly accurate portrayal of your fertile window. As new models enter the market, their accuracy may vary. These monitors can be expensive, however, starting at more than $150 for a starter kit and test sticks. For some people, this may be overkill. Many find the low-tech methods described earlier work fine in determining when their fertile window is likely to occur.

Apps and Wearable Tech

Numerous apps are available for tracking menstrual cycles, ranging widely in the information they collect and what guidance they offer. You might use an app only to record the dates of your period. Or you may find it helpful to log your basal body temperature, data about your cervical fluid, your mood, how much sleep you got, your energy level and more. Apps such as Natural Cycles — the first to be approved by the U.S. Food and Drug Administration (FDA) for pregnancy prevention — use algorithms to calculate the days during your cycle when you’re more likely to be fertile, based on the information you input about your menstrual cycle.

Some apps also can communicate with wearable tech devices, such as a smartwatch. This can make it quick or even automatic to upload information. Wearable fertility trackers include watches, bracelets and a ring, which can sense your temperature, heart rate and other signals.

Other Devices

Some monitors measure and store your daily basal body temperature and calculate your ovulation date and fertile periods based on temperature changes. However, as discussed earlier, temperature changes typically aren’t the most reliable way to detect your fertility window ahead of ovulation.

Hormone changes also may be reflected in your saliva to a degree. Some ovulation tests and fertility monitors use samples of saliva to detect changes in estrogen that accompany your fertility window. For example, some ovulation tests provide mini-microscopes you can use at home to observe samples of your saliva. When estrogen levels are high, special “ferning” patterns can be detected in dried saliva. When these patterns are present, your fertility is supposedly high. When they are absent, your fertility is considered low. Saliva-based fertility monitors collect and store information from saliva samples to help you determine high and low fertility days.

What evidence is available indicates that these methods are not as accurate in detecting the fertile window as urine-based tests or combined methods.

Don’t Be Afraid to Seek Help

Your body can provide valuable information about when you’re most likely to be fertile. But for many people, ovulation testing can be stressful. It can be easy to get so caught up in tracking all the various signs of fertility that you lose some of the spontaneity and fun involved in having sex.

Being aware of what’s happening with your cycle is an important step toward conceiving. But if you become frustrated or if the methods described don’t seem to be working for you, talk to your care provider or someone who’s well versed in natural family planning. They may be able to provide valuable information and advice.