No matter where you are in your menstrual cycle, there’s always a chance that you can get pregnant if you have sex without contraception (aka birth control). You might be thinking, “Wait, any time? Like, can you get pregnant on your period?” While the chances are slightly lower, it is entirely possible to conceive while you are menstruating.
Experts in This Article
board-certified OB/GYN
A few key factors can play into the likelihood of getting pregnant on your period, including the length of your menstrual cycle (i.e., the time from the first day of your period until the first day of your next period), the number of days you bleed, and when you had penetrative sex with a partner with a penis, Staci Tanouye, MD, an OB/GYN and sexual health advocate, tells Well+Good.
Want to know more? Read on to learn why it’s possible to get pregnant on your period, when you’re most likely to conceive throughout your cycle, and how to prevent pregnancy during that “time of the month” (if you’re not planning to get pregnant any time soon).
Why you can still get pregnant on your period
Before we dive into why conception during your period is possible, let’s brush up on a few basics. First, conception is most likely to occur when you ovulate (i.e., when your ovary releases an egg). When an egg is released, it travels down one of your fallopian tubes to your uterus, where it will meet with sperm if you’ve had unprotected sex. If the egg gets fertilized by the sperm, bam, conception happens. But there’s only a small window each menstrual cycle when this is possible—during ovulation.
Ovulation typically occurs in the middle of your cycle (on average, day 14 of a 28-day cycle, though everyone is different), and the egg is only available to be fertilized for 12 to 24 hours. If it’s not fertilized by then, it’s reabsorbed by your body, and then you shed your uterine lining41 (the bleeding during your period). While the egg only lasts a short time, “sperm can live inside you for up to five days,” Dr. Tanouye says. Some studies2 even suggest they may survive for as long as a week (in your fallopian tubes), she adds.
This means, if you have unprotected sex on your period, especially toward the end of your period, some sperm can stick around long enough to fertilize an egg if you ovulate about five to seven days later. This can specifically apply to those who ovulate earlier or later than average. (For context, only one-third of people ovulate between days 10 and 173 of their cycle. The rest, about 70 percent of people with uteruses, ovulate before or after this window.)
A bit confusing, right? Don’t worry: Here’s a breakdown of some of the more specific scenarios in which sex on your period can result in pregnancy, according to Dr. Tanouye:
1. You have short cycles
If you have a shorter menstrual cycle (aka any less than the average 28 days), you may ovulate only a few days after your period. This can cause an overlap between when sperm is in your reproductive tract (from unprotected sex) and when your ovary releases an egg, making pregnancy possible.
For example: “If someone has a 26-day cycle, then they are probably ovulating closer to day 12,” which is only five days after your period (if you menstruate for seven days), Dr. Tanouye says. So if you have unprotected sex on your period, your partner’s sperm may still be hanging around your reproductive system for five days (or even longer). That means a person “could potentially get pregnant if penis-in-vagina sex occurred as early as day five through seven [of their cycle], often when people are still on their periods.”
2. You ovulate earlier in your cycle
Remember: only 30 percent of people ovulate in the middle of their cycle. That means ovulation happens earlier (or later) for many. So even if you have the textbook 28-day cycle, you can still ovulate way before day 14. In other words, if you have unprotected sex on your period, and you ovulate a few days after, you can conceive by the sperm that is still lingering inside you.
3. Other factors led to an irregular cycle
Even if your periods are typically regular, some factors can throw your cycle out of whack on occasion. This can include stress, weight loss (or gain), certain medications, and uterine fibroids, among other things. If these factors cause your cycle to become shorter or longer one month, you may have a higher chance of pregnancy when you have sex while menstruating.
4. You have spotting between periods
Spotting between periods (aka breakthrough bleeding) is pretty common. It can happen for countless reasons—like forgetting to take your birth control pill, having endometriosis, or taking certain medications, just to name a few. But sometimes, it can be easy to confuse spotting with your period. Take the following scenario, for example: You see blood in your underwear, so you think you got your period. You proceed to have unprotected sex the same day (figuring the pregnancy odds are low), but it turns out it was just spotting, and a few days later, you ovulate when sperm are still inside you. This can up your odds for conception.
To make things even trickier, sometimes ovulation itself can cause light bleeding. In other words, you may think you’re on your period, but in reality, you’re having sex during the most fertile time in your cycle.
Can you get pregnant on your period while on birth control?
According to Dr. Tanouye, it’s highly unlikely to get pregnant during your period while on birth control. Whether you take the birth control pill or use the ring, patch, or injections, all these methods help prevent ovulation. And without an egg to be fertilized, you cannot get pregnant.
That said, birth control only works reliably if you’re taking it as directed. If you don’t use it properly (say, you forgot to take the pill or skip a day), “birth control could be less effective,” Dr. Tanouye adds. Plus, other factors can mess with birth control’s effectiveness, too, including taking certain antibiotic medications or having a stomach virus (which may interfere with the absorption of the pill), she says.
And keep in mind: Even when you use birth control correctly, there’s still a slight margin for error. “These methods are around 91 percent effective at preventing pregnancy,” Dr. Tanouye says. So if you’re not planning to become pregnant, it might be safe to use a combo of birth control strategies, say, condoms along with the pill for example.
What times of your cycle are you least (and most) fertile?
While cycle length varies from person to person, everyone’s menstrual cycle is made up of four phases. Depending on what phase you’re in, you have higher or lower odds of becoming pregnant. Here’s the breakdown of the four stages, including when you’re most and least fertile, according to Dr. Tanouye:
- 1.The menses phase (starts on the first day of your period): This is when you shed your uterine lining (i.e., period blood) if you’re not pregnant. As we learned, you’re not super fertile during this time, but it’s still possible to become pregnant.
- 2.The follicular phase (overlaps with the menses phase and ends when you ovulate): During this time, the lining of your uterus (the endometrium) grows and thickens and follicles in your ovaries begin to grow. Between days 10 and 14, a fully mature egg (ovum) will form. The second half of the follicular phase (i.e., right before ovulation) is a very fertile time, Dr. Tanouye says.
- 3.Ovulation (typically happens around the midpoint of your cycle, i.e., about day 14 in a 28-day menstrual cycle): Your ovary releases an egg that can be fertilized by sperm, but it’s only viable for 12 to 24 hours. This short window is your peak of furtiveness.
- 4.Luteal phase (lasts from about day 15 to day 28 in a 28-day cycle): This phase is when an egg leaves your ovary and begins to travel through your fallopian tubes to your uterus, where the lining thickens to prepare for a potential pregnancy. If the egg is fertilized by sperm and attaches itself to your uterine wall (implantation), you become pregnant. If not, the thick uterine lining sheds during your next period. Your chances of conceiving 24 hours after ovulation are slim, so you’re probably the least fertile during this phase, Dr. Tanouye says.
To sum up:
- You’re most likely to get pregnant when you have sex right before and during ovulation.
- You’re least likely to get pregnant 24 hours (and beyond) after ovulation.
- While your period isn’t your most fertile time, you can still conceive.
How to prevent pregnancy while on your period
If you don’t want to get pregnant, you’ll need to use some form of contraception. Luckily, there are many options to choose from, and you can talk to your healthcare provider about which is the best fit for you. Here’s a breakdown of the most common types:
- Hormonal birth control: Birth control methods like the pill, ring, patch, shot, and intrauterine devices (IUDs) work by preventing ovulation.
- Condoms: “Barrier methods [like condoms] are the only methods that prevent STIs,” Dr. Tanouye says. They provide an extra layer of security especially if you use them along with other birth control methods.
- Abstinence: If you’re not on birth control and/or don’t have access to other barrier methods, you might want to abstain from penis-in-vagina sex during your period or other fertile times in your cycle.
- Natural family planning (NFP): This method involves tracking your menstrual cycle so you can accurately predict when you’re ovulating. For example, you’ll have to pay very close attention to your symptoms, including changes in your cervical mucus and your basal body temperature (which rises slightly after ovulation), Dr. Tanouye says.
- The morning-after pill: This method, also known as “Plan B,” works by preventing your body from releasing an egg. It’s most effective if you take it as soon as possible after unprotected sex, though you can take it within a five-day window. However, because the morning-after pill doesn’t work as well as other forms of birth control, it’s best to use it only in emergencies—i.e., when you didn’t use birth control or it failed (think: the condom broke).
The final takeaway
If you have unprotected sex with a partner who has a penis, it is entirely possible to get pregnant during your period. Certain factors—like short, irregular cycles or early ovulation—can increase your chances of conceiving during menstruation. But, still, it’s not very probable, especially if you have sex on the first few days of your period. In other words, if you’re actively trying to get pregnant, this is not the best time to have sex.
That said, if you’re trying to avoid pregnancy, always use some form of protection during sex (or a combination of methods). Your healthcare provider can help you decide which is right for you.
And if you’re unsure whether you are pregnant? Consider picking up an at-home pregnancy test at your local pharmacy or visiting your healthcare provider for a test in-office.
Critchley HOD, Maybin JA, Armstrong GM, Williams ARW. Physiology of the Endometrium and Regulation of Menstruation. Physiol Rev. 2020 Jul 1;100(3):1149-1179. doi: 10.1152/physrev.00031.2019. Epub 2020 Feb 7. PMID: 32031903.
↩︎Kölle, Sabine. “Sperm-oviduct interactions: Key factors for sperm survival and maintenance of sperm fertilizing capacity.” Andrology vol. 10,5 (2022): 837-843. doi:10.1111/andr.13179
↩︎Wilcox, A J et al. “The timing of the “fertile window” in the menstrual cycle: day specific estimates from a prospective study.” BMJ (Clinical research ed.) vol. 321,7271 (2000): 1259-62. doi:10.1136/bmj.321.7271.1259
↩︎Critchley HOD, Maybin JA, Armstrong GM, Williams ARW. Physiology of the Endometrium and Regulation of Menstruation. Physiol Rev. 2020 Jul 1;100(3):1149-1179. doi: 10.1152/physrev.00031.2019. Epub 2020 Feb 7. PMID: 32031903.
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