If you're relying on your menstrual cycle as a form of birth control, you might be surprised to learn that you can, in fact, get pregnant on your period.
Sure, it's one of the less fertile times of the month, but under some conditions, conception could occur.
How can you get pregnant on your period?
The chances of getting pregnant when you're on your period are low, but they're not zero. So how could a pregnancy happen at the same time your body is deciding it’s not pregnant?
Let’s break it down: At ovulation, your ovary releases an egg into your fallopian tube, where it can live for 24 hours awaiting fertilization before the early embryo begins its travels to the uterus. Meanwhile, the uterus is building up a lining just in case it needs to host a growing embryo.
If egg meets sperm during ovulation and implants in that lining, bingo — baby on board. If not, your body sheds both lining and egg (and … you’re bleeding).
Most women’s menstrual cycles last about 24 to 28 days, from the first day of their period to the first day of the next period. Because the egg can survive for 24 hours after ovulation and sperm can live inside a woman for up to five days, a woman can get pregnant starting five days before ovulation and ending a day after.
Ovulation usually occurs 14 days before the first day of your next cycle — which, if you have a 28-day cycle and a week-long period, leaves you a week between the last day of your period and the first day you ovulate.[1]
But what if you have sex on the last day of your period and you ovulate a few days early? There could still be viable sperm inside you, and you could get pregnant.
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Even in a woman who has a 28-day cycle, the day of ovulation starts vary from month to month. Because of this fluctuation, you can’t guarantee the sperm from the sex during your period will be dead by the time you ovulate next.[2]
Can you get pregnant on your period if you have an irregular cycle?
Yes. If you have an irregular period, it can be harder to predict when you’ll be ovulating — and that could cause you to get pregnant accidentally, since it can be harder to avoid having sex close to that time.[3]
Here are a few types of irregular menstrual cycles, and how it's still possible to get pregnant:[4]
- You have a short cycle. Some women have cycles as short as 21 days and still ovulate, which means they don’t have as much time between when they finish menstruating and when they next ovulate. And since sperm can live in your reproductive tract for a few days, if you happened to have sex during your period and then ovulated the following cycle’s egg two to three days later, that egg could encounter viable sperm. And you know what that means.
- Your periods last a long time. While your body is slowly shedding that uterine lining, the clock is ticking on ovulation — and your next egg shows up while you’re still bleeding from the previous month’s (non-fertilized) egg. So you’re already fertile again — which means you can get pregnant on your period.
- You have breakthrough bleeding, or spotting, when you ovulate. Especially if you have light or irregular periods, it would be easy to mistake this bleeding for a true period — even though it’s happening when you’re actually most fertile, since you’ve just ovulated.[5]
Sometimes, however, an irregular period can be a sign that you're not ovulating at all, which is one cause of infertility. (You can't get pregnant if you don't ovulate.) Breakthrough bleeding can also be a sign of hormonal abnormalities or a physical abnormality in your uterus (such as polyps, fibroids or an overly thick lining), so bring it up with your doctor even if you are not trying to get pregnant if it persists.
If you have an irregular menstrual cycle and you've had trouble getting pregnant, talk to your doctor, who may want to do a further evaluation.
Can you get pregnant right before your period?
It’s not impossible, but it is unlikely — especially in women with regular, 28-day cycles. Ovulation is normally complete by day 19, a solid week-and-a-half before your next menstrual period begins.
That said, ovulation is harder to predict in women with irregular periods, which means it could happen later in the cycle. Plus, even in women with regular cycles, ovulation can vary from month to month, especially if you're stressed, traveling or changing up your normal routine.
Can you get pregnant on the first day of your period?
It's possible — though not very likely — for you to get pregnant on the first day of your period, especially if you have a regular, 28-day cycle.
If you have an irregular or a shorter menstrual cycle, however, ovulation might occur much closer to day one of your period, which would cause you to get pregnant on the first day.
Can you get pregnant right after your period?
Yes, you can get pregnant right after your period. The likelihood of this happening, however, depends again on when you ovulate. In women with a 28-day, regular cycle, ovulation usually begins at day 14, which would be seven days after the end of a week-long period.
If you ovulate early, or if you have a short menstrual cycle or a long period, the amount of time between your period and ovulation could be much less. Also, because sperm can stick around for five days, sex only a day or two right after your period could lead to a baby.
Can you get pregnant on your period while using birth control?
It's possible to get pregnant when you're using birth control, whether you're on your period or not. (The only 100-percent-effective type of birth control is abstinence.)
The likelihood that a contraceptive will fail varies depending on the method of birth control (based on typical use):[6]
- Intrauterine devices (IUD): Less than 1 percent failure rate[7]
- Implant: Less than 1 percent failure rate
- Injection: About 4 to 6 percent failure rate
- Oral contraceptives (“the pill”): About 7 to 9 percent failure rate
- Progestin-only pill: About 7 percent failure rate
- Patch: About 7 to 9 percent failure rate
- Vaginal contraceptive ring: About 7 to 9 percent failure rate
- Male condoms: About 13 to 18 percent failure rate
- Diaphragms: About 12 to 17 percent failure rate
For what it's worth, tracking your monthly cycle — called "fertility awareness" — in order to avoid pregnancy isn't the most reliable birth control method; the typical failure rate may be as high as 23 percent.[8]
The bottom line: Although the odds are slim, you can get pregnant on your period — or any other time of the month. It's even possible (though not as likely) to get pregnant on your period if you're using birth control.
So unless you’re trying to conceive, it’s always smart to be vigilant about contraception — unless you like big surprises.
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