How Long Does It Take to Get Pregnant?

Many factors determine whether a person will conceive after sex, including birth control use, age, fertility, or just plain chance. However, 85% of sexually active people between ages 15 and 44 who don’t use any birth control will become pregnant within a year, according to a 2011 study.

The process of conception usually takes two to three weeks after intercourse, according to Planned Parenthood. It involves ovulation (egg release), sex with the penis in (or near) the vagina, ejaculation of sperm, fertilization of the egg, and implantation of the fertilized egg in the uterus, after which pregnancy symptoms will start to develop.

Fertilization happens when an egg and a sperm cell (spermatozoon) unite to form a single cell. After fertilization, that cell travels down the fallopian tubes to implant itself in the lining of the uterus. If implantation is successful, the embryo starts to grow. Pregnancy is assumed to start two weeks after the first day of a person’s last period, even if some of that time includes not being pregnant.

Ovulation

Ovulation involves the release of a fully mature egg from one of a person’s two ovaries. Assuming that no contraception is being used to prevent ovulation, it usually occurs at about day 14 of a 28-day menstrual cycle. Then the egg takes about five days to travel down one of the two fallopian tubes to the uterus. Meanwhile, hormones such as estrogen and progesterone are rising in the body to help prepare the uterine lining for pregnancy.

The egg is only capable of fertilization for 12–24 hours. This is why some people use at-home ovulation tests to predict when they are at their most fertile and time intercourse to happen around then. If fertilization does not happen, the thickened uterine lining is shed during your period, and the cycle starts all over again.

Occasionally, more than one egg is released during ovulation. If all are fertilized, they can result in multiple pregnancies. Fraternal twins are conceived this way, with two eggs. In identical twins, one fertilized egg splits into two.

Ejaculation

Sperms are ejaculated from the penis into the vagina—a lot of them—during sex without a condom. All of the sperm are vying to fertilize one egg, in most cases. Unless contraception is used, some of them can travel through the cervical mucus guarding the entrance to the uterus and upward into the fallopian tubes, where they can live for up to five days. So it’s possible for fertilization to happen even a few days after intercourse.

Fertilization

If just one sperm penetrates the egg, the egg won't allow other sperm in, and the resulting single cell is known as a zygote. It gets half of its 46 chromosomes from one parent and half from the other.

Cell division begins during the roughly weeklong journey that it takes the growing cluster of cells to travel down the fallopian tubes and into the uterus. Once it reaches about 100 cells in size, it is known as a blastocyst. 

Implantation

About a week after fertilization (and up to nearly two weeks after intercourse), the blastocyst emerges from its shell and attaches itself to the uterine lining, also known as the endometrium. Implantation can take three to four days to complete. During this time, the placenta connecting the mother and embryo develops. Its job will be to supply the growing embryo with oxygen and nutrients through the mother and to filter out waste.

After implantation has taken place, the embryo begins to grow. At this point, two to three weeks may have elapsed since intercourse. However, about half of all naturally fertilized eggs do not implant and are lost before the next menstrual cycle begins.

If a pregnancy has occurred, then the body will release hormones to prevent the lining from being shed and to further prepare the body for gestation. Starting from nine weeks after implantation until birth, the term for the baby changes from "embryo" to "fetus."

Pregnancy Symptoms

The first sign of pregnancy that a person may notice is a missed period. Other common early signs are:

• Nausea and vomiting (also known as morning sickness, thought it can happen at any time of day)
• Fatigue
• Swollen or tender breasts
• Bloating
• Constipation
• Urinating more frequently than usual

Summary

It takes two to three weeks to get pregnant after unprotected intercourse. Pregnancy is said to start two weeks after your last period. If you suspect that you are pregnant, confirm it with your primary care clinician or an obstetrician-gynecologist. They will also be able to instruct you on the next steps.

It can take a surprisingly long period of time after sex to become pregnant: about two to three weeks. Even if the egg is fertilized, it may not implant in your uterus, and pregnancy may not occur. It’s important to understand the timeline from ovulation to implantation—whether or not you wish to conceive—so you can make informed choices about sex and pregnancy.