Can you get pregnant on or right after your period?

You may have heard you can't get pregnant on your period, but that's not true. While it's not the most likely time to conceive, there are factors – such as the timing and the length of your menstrual cycle and when you ovulate – that make it possible to get pregnant on your period.

For most women with regular periods, the chance of getting pregnant is highest the five days before ovulation and the day of ovulation.

"The highest likelihood is on the day before ovulation," explains Amanda AdeleyeOpens a new window, M.D., an assistant professor of obstetrics and gynecology at the University of Chicago. "That doesn't mean you can't get pregnant any other time during your cycle, though!"

Here's a rundown of your chances of getting pregnant during your period, and on the days before and after it.

How can you get pregnant on your period?

It's possible to get pregnant during your period when you have a short menstrual cycle, especially when combined with a long period.

Because a typical menstrual cycle is 28 days, that usually leaves a good few days between the end of your period and the start of ovulation. But some women have cycles as short as 21 days. That means there's less time between the end of your period and your next ovulation.

"For most women, a normal menstrual cycle ranges from 21 to 35 days," explains the Eunice Kennedy Shriver National Institute of Child Health and Human Development.Opens a new window "However, 14 to 25 percent of women have irregular menstrual cycles."

Your menstrual cycle can vary from one month to the next. Also, cycles last longer when you first start menstruating and tend to become shorter and more regular as you age. According to the U.S. Department of Health & Human Services Office on Women's HealthOpens a new window, cycles are most regular in your 20s and 30s. In your 40s – when your body starts the transition to menopause – periods may become irregular.

If you have a short cycle, you could ovulate right after your period ends (mid-cycle of a 21-day cycle could be on day 10 or 11 since the start of your period). And because sperm can survive in your reproductive tract for up to five days, if you have sex during your period, it's possible that live sperm will be there when you ovulate, ready to fertilize the egg.

Having a long period would make this even more likely. If your period lasts 7 days and you ovulate on day 10, that would mean having sex on day 7 would provide sperm for fertilization on day 10 when the egg becomes available.

Another possibility is that you mistook mid-cycle bleeding for your period. (This is more likely to happen if you usually have pretty light periods.) Spotting between periods can be a sign of ovulation that occurs when the follicle surrounding the egg breaks open. It can happen all at once or for a few days. If you had unprotected sex at that time, thinking you were having your period, you could conceive. In fact, you'd be very fertile!

Can you get pregnant right after your period?

Yes. Immediately after your period isn't the ideal time to get pregnant, but you're more likely to conceive at this time than during your period. That's because you're closer to the time when you'll ovulate.

Again, two factors can increase your chances of getting pregnant right after your period:

1. A short menstrual cycle
2. A long period

The shorter your cycle and the longer your period, the more likely it is that you'll be fertile during the last few days of your period or in the days just after it ends.

So, for example, if your period lasts for a week and you have sex on day 8, you're pretty close to your fertile time (from day 11 to day 21). Remember, sperm can live for five days inside your body, so they can make it from day 8 to day 11!

Can you get pregnant right before your period?

Yes, but it's unlikely. In general, you're least likely to get pregnant in the days before your period. As you start your period, and then reach the end of it, your likelihood goes up.

But while chances of getting pregnant right before your period are low, it can happen.

"You might become pregnant right before or early in your period if your egg reserve is rapidly decreasing (because you're entering perimenopause, for example)," explains Sasha HakmanOpens a new window, a board certified ob-gyn and board-eligible reproductive endocrinology and infertility specialist. "This is because your brain sends early signals to the ovaries to recruit new eggs before the current cycle is over."

Can you get pregnant on the first day of your period?

This can happen if a woman is starting to transition into menopause or is prematurely running out of eggs. The brain is constantly sending signals to the ovary to recruit and mature more follicles that contain eggs. This may cause an "out of phase" ovulation during your previous menstrual cycle.

Learn more:

• Is it possible to get pregnant while breastfeeding?
• How soon after giving birth can you get pregnant?
• The best time to get pregnant