We all sit through awkward and embarrassing Sex Ed classes in high school, but when it comes down to it, none of us really learned when to actually have sex during your cycle in order to get pregnant. In fact, we didn’t really learn much of anything useful about our menstrual cycles. Like, what even happens to us every month? And what does any of it have to do with getting pregnant?
Now that you’re in the phase of life where you might be trying to get knocked up, a little info would go a long way. So imagine we’re your junior-year P.E. teacher, because we’re about to tell you everything you need to know about what your uterus gets up to every month. Spoiler alert: it basically has a life of its own.
I’ve heard there are different phases of my cycle…is that true?
Yup. Your monthly cycle is divided up into two phases: the follicular and the luteal. The follicular phase starts when your period kicks off and lasts about two weeks, ending when you release a ready-to-be-fertilized egg in ovulation. Once that happens, you move into the luteal phase, which also lasts about two weeks and ends when you get your period. Then the whole process starts alllllll over again.
Most menstrual cycles are about 28 days, on average, but really there’s a range of normal here. According to the Mayo Clinic, a cycle can last anywhere from 21 to 35 days.
What happens during each phase?
Let’s pretend you have a totally textbook 28-day period (yeah, we know—you’re not a robot, but just go with us here).
On the first day of the follicular phase, Aunt Flo shows up for a visit. You’re crampy and bloated and cranky and bleeding. (So. Much. Fun.) But according to Dr. Jane Frederick, reproductive endocrinologist at HRC Fertility in Orange County, California, there’s also hormonal stuff happening, too: your brain is secreting hormones from your pituitary and sending signals to your ovary to stimulate egg production. You’ll bleed for about 3 to 7 days and then have 7 to 10 days where not a whole lot goes on that you can see.
But behind the scenes, explains Frederick, your hormones are communicating like crazy. At some point, the dominant follicle in your ovary will produce estrogen and then send a message back to your brain: Stop sending egg production signals…I’m ready to ovulate! The ovary releases the egg and it moves through your fallopian tubes. (This is the point in your cycle when you could become pregnant, but we’ll circle back to that in a few.)
Once ovulation is complete, you move into the luteal phase. If you have a 28-day cycle, it’s probably about day 14 of your cycle, give or take. Now your hormones are doing a Freaky Friday-style switcharoo: the estrogen that peaked before ovulation is dropping and your progesterone levels are rising instead. According to Dr. Frederick, if you have a fertilized egg, progesterone will help it implant in the lining of the uterus and develop successfully into a pregnancy.
On the other hand, if your egg didn’t get fertilized during ovulation, your progesterone levels drop and your endometrial lining starts to shed in menstruation. Aunt Flo’s back in town again!
Okay, but when am I most fertile?
Despite what your sex ed teacher might have told you, a woman can only get pregnant during a very short window of time every month. And that’s right around the time of ovulation, because once the egg has been released from the ovary it’s only good for 24 hours, which would be considered your fertile window.
So if you’re looking to become pregnant, you either want to have some sperm already swimming around in your reproductive tract ready to pounce (pro tip: those guys can survive in there for up to 5 days), OR make sure you have sex within that magic 24-hour window as this is when a female is most fertile.
To be clear, when exactly is my fertile window?
This part can be tricky as everyone’s fertile window is different. If you don’t have a perfect 28-day cycle, pinpointing ovulation closely enough to get your conception timing right can feel like a guessing game. The good news is that there are ways to figure out when to have sex to get pregnant.
The best way to indicate your fertile window is by monitoring your cycle. Luckily, there are ovulation calculators and easy-to-use tracking apps on your phone that are super simple to implement in your daily life.
But getting back to your fertile window, it all depends on the length of your cycle. Every woman’s cycle length varies, but the commonality is that ovulation occurs about 14 days before your next period with your most fertile days typically being the 3 days leading up to ovulation, including the day of ovulation.
For example, if you have a 28-day cycle, you are expected to ovulate around day 14 with your most fertile days being days 12, 13, and 14. Whereas, if you have a 24-day cycle you’ll be ovulating around day 10 with days 8, 9, and 10 being your fertile window.
But wait…can you get pregnant on non-fertile days?
The honest answer is that you must be fertile to conceive, but this doesn’t necessarily mean that you can only have sex on the days you are fertile to become pregnant. As previously mentioned, those little swimmers known as sperm can survive in a woman’s reproductive tract for up to 5 days. That means if you have unprotected sex on day 7 of your cycle but don’t ovulate until day 12, you may still have a chance of becoming pregnant. While the odds may not be as favorable compared to your ovulating day, it’s still possible.
Does that mean I can get pregnant during my period?
If you have unprotected sex during your period, it is possible to get pregnant depending on the length of your period and when your fertile window occurs. Going back to the example, a 28-day cycle means that you are fertile during days 12, 13, and 14. Therefore, if you have sex on day 7 of your cycle and you still have your period, you may very well end up pregnant since the sperm is able to survive within the reproductive tract for 5 days.
Am I considered fertile after my period, too?
Depending on what days you are talking about, the answer can be yes or no. If you have sex during your fertile window or five days prior to your fertile window, there is a possibility of becoming pregnant. However, after you reach that day of ovulation and the released egg does not become fertilized within that 24-hour window, your egg jumps ship and heads on down to your uterus since it knows it won’t meet its match this time. Your hormone levels then begin to go back to normal, your uterine lining will shed, and cause you to menstruate to start your cycle all over again.
In other words, this means that your chances of becoming pregnant after ovulation continue to go down.
Wondering if you’re fertile after having a baby?
Whether you’re looking to add some more limbs to the family tree, or just want a break from pregnancy…no judgment. The chances of becoming pregnant right after giving birth vary for each woman. Depending on a few factors, women may experience their first postpartum period anywhere from four weeks after giving birth to 24 weeks! That’s quite a difference, which is why if you’re trying to plan your next pregnancy, contraception will be your best friend until you have a better sense of your cycle.
Tracking your fertile window
As we mentioned, the best way to determine your fertile window is to monitor your cycle. You can use some of the many mobile apps or online calculators that exist, but you can also do some simple math in your head or predictor kits if you want precise indications.
Ovulation predictor kits
Around day 10 of your cycle, you can start peeing on a stick to see whether or not you’re ovulating yet. Dr. Frederick says it’s best to do this in the evenings after you’ve been hydrating all day. If you see a positive indicator for ovulation, she recommends having sex that night and the next night to optimize your pregnancy chances. Cue the Marvin Gaye!
You ovulate about 12 to 16 days before you start menstruating, so you can spend a few months keeping track of how many days your cycles usually are and counting back from the first day of your period to figure out which days in your cycle are prime ovulation territory.
To get pregnant, you would want to have sex for several days during that window. A recent Fertility and Sterility study suggests that daily sex during your fertile window will be the most successful—especially if you do it the day before ovulation. However, some doctors still recommend sex every other day to build a good supply of sperm.
Other fertility awareness methods
Are you ready to get down and dirty with your fertility? These methods are not for slackers, but they can be pretty effective in calculating your day of ovulation if you’re willing to commit. There are a few different varieties, but basically you’ll need to take and chart your basal body temperature (BBT) each morning the second you wake up with a super-accurate thermometer and/or keep tabs on your cervical mucus throughout the day by fishing around in your vagina to see what’s up down there.
Why? Because your body goes through several natural changes throughout your cycle, which you can observe if you’re paying enough attention. Around the time of ovulation, for example, your cervical mucus becomes slippery and stretchy, like egg whites—and right after ovulation, your BBT spikes by a few decimal points. If you know when this stuff is happening and chart it, you can become, like, a total fertility detective (which might eliminate all that pesky ovulation guesswork).
One disclaimer: Dr. Frederick says that tracking ovulation works best when you ovulate regularly, so if you only get one period every 45-60 days, tracking ovulation will be much trickier (though not impossible). There are tons of apps out there that make cycle tracking a breeze if you’re not a pen and paper kind of gal.
Summing it up
Here’s the moral of this story: if you’re trying to get pregnant, start tracking your cycle. If you really want to get crazy, grab a basal thermometer, get familiar with your cervical mucus, and start tracking all that stuff, too. Understanding your cycle does not have to be one of life’s great mysteries. Knowledge is power, girl—go get some.
Co's Picks for Best Ovulation Test Kits