If you’re trying to conceive, knowing how to calculate your fertile window is key. 


By Dr. Nazaneen Homaifar

Finding your “fertile window,” those special few days when you’re likeliest to conceive, can be a tricky task. 

We’ve designed ourOvulation Test Kit with a tracker to help you decode your body’s signals. You’ll be able to find your fertile window much more successfully if you understand the ins and outs of your cycle. We hope this can help you set your mind (and body) at ease!  

What is ovulation?

A woman’s menstrual cycle is usually about 28 to 35 days long (some can be shorter or longer, and that’s normal). This whole affair begins on cycle day one, the day you get your period. Day one marks the beginning of the follicular phase of your cycle, which is named for the tiny fluid-filled sacs called follicles in your ovaries that hold immature eggs.  

About halfway through your cycle, a colorful cast of hormones triggers the process of ovulation: when a mature egg is released from your ovary. The egg ventures down your fallopian tube where, if you’ve done the math right and timed sex well, sperm can travel to fertilize the egg, eventually creating an embryo. 

After you ovulate, the follicle transforms into the corpus luteum, a cyst that supports the pregnancy by producing progesterone; the uterus prepares for implantation of the embryo by thickening it’s lining. This part of your cycle is called the luteal phase.

If fertilization does not occur, the corpus luteum will stop producing progesterone and break down, and the uterine lining will shed, resulting in another period. 

So, what’s a fertile window?

A woman’s “fertile window” is the five-day period of time leading up to ovulation, plus the day of ovulation itself (so, six days total). Since sperm can live inside a woman’s body for up to five days, having sex at the beginning of your fertile window before an egg is released can still lead to pregnancy. 

Some women experience noticeable signs of ovulation like abdominal pain (called mittelschmerz, German for “middle pain”), light spotting, breast tenderness, bloating, and an increased sex drive. But for those of us who don’t experience these signs, or who have erratic cycles, it can be tough to tell. If you’re in that boat, keep reading for some ways to determine your fertile window.

Ovulation tests

Ovulation tests come in all sorts of flavors. Some are midstream (which you pee directly on) and some are test strips you dip in urine. All of these types of tests detect the presence of something called luteinizing hormone (LH) in urine. LH is one of the key players in your monthly cycle. The LH surge (increase in hormone level) triggers ovulation, or the release of an egg.

LH levels spike—or “surge”—16 to 48 hours before ovulation. Ovulation tests detect this surge and can help identify your fertile window. A positive ovulation test means you are in your “LH surge” and that it’s an ideal time to have sex if you want to get pregnant. Keep in mind, you’ll want to know your pattern of ovulation (what day in your cycle you get a positive test) for future months in order to time sex before the surge and make use of the full fertile window. Our Ovulation Test Kit comes with a free ovulation tracker where you can record what day and time you took your ovulation test and whether the results were positive or negative.  

Of course, sex can’t always be scheduled like a business meeting. Having an honest discussion with your partner, and planning how to go about this together will make the process easier (and won’t kill the mood). 

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Cervical mucus tracking 

Monitoring your cervical mucus can also help you identify your fertile window. You’ll notice a section of our tracker dedicated to this, as well. Using a fertility lube can help simulate the natural environment where human sperm thrive—fertile cervical mucus.

Cervical mucus (aka vaginal discharge) is a fluid produced by your cervix. The cervical mucus produced right before and during ovulation is translucent, stretchy, and more copious. It has a similar consistency and appearance to egg whites. This is called fertile-quality cervical mucus because it’s ideal for helping sperm move along their journey into the uterus and fallopian tubes.

To test your cervical mucus, simply insert a clean finger into your vagina, and note the color and consistency of the sample. If it’s sticky, thick, or dry, you are likely not in your fertile window. If it resembles egg whites and is stringy, you are likely near ovulation and in your fertile window

Detecting Ovulation From Cervical Mucus

Detecting Ovulation From Cervical Mucus

Basal body temperature 

You’ll also see a section on the tracker for capturing basal body temperature (BBT). The progesterone that is released from the corpus luteum after ovulation actually affects a part of your brain that regulates temperature, called the hypothalamus. Progesterone increases the temperature of the body ever so slightly, and this temperature change is what we measure with the basal body temperature. Your basal body temperature (BBT) changes subtly right around ovulation, and those changes can be used to determine when you are in your fertile window. BBT is an indicator of when you ovulated, not when you will ovulate

When you ovulate, your BBT will rise about half a degree (0.5℉) for ten days. To track your BBT, you need to buy a special thermometer—one that measures up to a one-tenth of a degree. Good news is they’re cheap and available in pharmacies and supermarkets, as well as online. 

BBT tracking is the most labor intensive and error prone option of the three options discussed here. You are required to take your BBT immediately when you wake up, before you even sit up for the day. If you forget, that day’s reading is lost. In a study performed to test the accuracy of BBT tracking, 20% of women did not show changes in BBT despite regular ovulation confirmed via blood hormone level checks. 

To reiterate, a key difference between BBT and the other tracking methods in this article: your BBT will increase right after ovulation. This means that you can’t use BBT to identify your fertile window for your current cycle. But if you track when this temperature rise occurs month-to-month, it can be helpful in predicting when your fertile window is likely to occur in the following months.  

Natalist’s ovulation tracker 

Our ovulation tracker, which is included for free in our Ovulation Test Kit, allows you to record your cycle effectively and reliably. Tracking these different aspects of your cycle will make it easier to find your fertile window and have sex at the most opportune time. Even if your cycle is irregular, it can be a good idea to use this ovulation tracker to document your periods over a few months to get a sense for whether your body is indeed following any patterns. 

If you’re having trouble conceiving, you’re not alone! You can show your trackers to a gynecologist or fertility specialist to get an expert opinion. Having this information, even if you’re struggling to conceive, can help you have a more educated and directed conversation with a physician. 

We hope this tracker can be a helpful tool on your journey to conception! Sometimes the fertile window can feel elusive, but hopefully one of the methods we discussed above will help you get a handle on your unique cycle. 

Interested in more strategies, tips, and advice to increase your chances of getting pregnant naturally? Read “Tips to Increase Your Chances of Getting Pregnant This Month”.