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When are you most fertile? How to tell when you're more likely to get pregnant

Whether you’re trying to get pregnant or trying to make sure you don’t, here are a few fertility basics.
/ Source: TODAY

Growing up, getting pregnant seemed like an absolute outcome of sex rather than a calculated science based on your fertility window.

Yes, of course, you can get pregnant from sex. And when you’re not trying to get pregnant, you should be using precautions to prevent pregnancy whenever you’re sexually active.

But unlike what was drilled into our minds as teens, you aren't likely to get pregnant every single time you have sex. In fact, getting pregnant depends on when you are most fertile each month and there are specific days when you can and can’t get pregnant.

The truth is that most women only have a short window each month that they will be able to get pregnant. Sometimes, the window is just hours long.

When are you most fertile?

Whether you’re trying to get pregnant or trying to make sure you don’t, understanding a few fertility basics is key according to Dr. Jill Purdie, a board certified OB-GYN and medical director at Pediatrix Medical Group.

"A woman is the most fertile at the time of ovulation," Purdie tells "Ovulation is when the egg is released from the ovary. For the majority of women, ovulation will occur about 14 days before the menstrual period begins."

Purdie says the timing of ovulation depends on the length of the menstrual cycle.

"Women can typically get pregnant about three to four days prior to ovulation and one to two days after ovulation," she says.

How many days after your period are you most fertile?

Fertility is linked to menstruation, so iff women have a regular menstrual cycle, the fertile window should be predictable.

The first day of menses is day one of the cycle.

"If a person has a 28-day cycle, ovulation will occur at day 14 and the next period will start 14 days after that," Purdue says. "If the person has a shorter cycle, say 25 days, ovulation will occur sooner around cycle day 11."

If the cycle length is longer, ovulation occurs later.

"The time from ovulation until the next period begins is typically 14 days for everyone," Purdie explains.

According to the American College of Obstetricians and Gynecologists (ACOG), an egg can only be fertilized for about 24 hours following ovulation, while a man's sperm can live in a woman's body for anywhere between three and five days.

Fertility window calculator

When are you most fertile?
Ovulation and menstruation apps can help track your cycle and enable to better predict when you're in the window of fertility. myflo period tracker

For women with an irregular cycle, tracking ovulation may be a bit harder; however, these women do have options.

"They can look for signs of ovulation, such as increased cervical discharge," Purdie says. "They can also use basal body temperature charting."

With basal body temperature charting, women check their temperature first thing in the morning and chart it on a graph.

"Women will typically get an increase in their body temperature the day after they ovulate," Purdie says.

Women with irregular cycles may also use ovulation predictor kits.

"These kits detect the hormone LH, which is responsible for causing the ovary to release the egg," Purdie says. "The LH level will typically spike the day prior to ovulation."

Tracking overall fertility

If you want an even clearer picture of what's happening inside your body, it's important to pay attention and track ovulation. In order to conceive, there must be an egg, sperm and open fallopian tubes. Purdie tells that tracking ovulation assesses if an egg is being released.

"Women are born with all the eggs they will ever have, and the eggs age as the woman ages," she explains. "There are blood tests that can be done to predict ovarian reserve to determine if a woman has a reasonable number of eggs remaining; however, there is no test to look at quality of those eggs."

As a woman's eggs age, the quality goes down.

"This means the ability for the egg to be fertilized and develop into a healthy embryo decreases with age," she says. "For the sperm, the partner can give a sample for analysis. This sample looks at the sperm count, motility and anatomy of the sperm."

There is also a test called a hysterosalpingogram (HSG) that is done with a radiologist and can assess if the fallopian tubes are open.

Purdie tells the chance of conceiving each menstrual cycle is approximately 20% to 25%.

"This number does decrease as the woman ages since the quality of the eggs decreases," she says.

A couple is officially diagnosed as infertile once they have tried for 12 cycles without conceiving.

"Couples may choose to have an evaluation after six months if they desire," Purdie says. "Especially in women over 35."