How Many Weeks Pregnant Am I?

Many people find themselves puzzled when trying to figure out how far along they are in pregnancy. Even those who have carefully tracked their menstrual cycles or believe they know exactly when conception occurred can still feel uncertain about their due date.

This confusion is common and nothing to worry about, especially in the early weeks of pregnancy. Understanding how pregnancy weeks are counted and what they really mean can help provide more clarity during this important time.

How Many Weeks Make Up a Typical Pregnancy

Pregnancy lasts about 40 weeks from the start of the last menstrual period. This method uses the first day of a woman’s menstrual period, even though ovulation or conception may not have happened yet. By the time ovulation occurs, a person is already counted as being two weeks pregnant.

Pregnancy is divided into three trimesters, each marked by different hormonal and physical changes. Some pregnancies last a bit less or more than 40 weeks. Blood tests and ultrasound exams help measure gestational age and monitor for preterm or full-term delivery. This calculation always starts with the last period date, regardless of when egg retrieval, conception, or embryo transfer occurs.

Dating Your Pregnancy After a Positive Test

Most home pregnancy tests check for hCG hormone in urine, which increases soon after embryo implantation. Typically, a positive result appears about five to six days before the expected period. At this stage, a person is usually just over three weeks pregnant, counting from the first day of their last menstrual period (LMP).

By the day the period is expected, pregnancy is usually counted as four weeks along for those with a regular 28-day cycle. Tracking the date of the last period helps estimate how many weeks pregnant someone is once they see a positive result.

Ways to Find Your Due Date

Figuring Out Your Due Date from Your Last Menstrual Cycle

Most healthcare providers estimate the expected date of delivery (EDD) using the first day of the last menstrual period. They typically add seven days to this date, then count back three months. For example, if the LMP was March 1, adding seven days gives March 8, and moving back three months points to December 8 as the estimated date of confinement. This calculation assumes a regular 28-day cycle.

Using the Day of Conception

Those who know exactly when they ovulate may find this method more accurate. When people use ovulation tracking or test kits, they can calculate the estimated due date by counting 266 days from the known conception date. Keep in mind, sperm can survive for several days inside the body, so conception might not be the same as the date intercourse happened.

Calculating Due Date with IVF Transfer

For pregnancies using in vitro fertilization (IVF), the embryo transfer date serves as the baseline. Count 263 days from a Day 3 transfer, or 261 days from a Day 5 transfer, to get the estimated due date. This method applies specifically to IVF patients because embryo age at transfer is known exactly.

Checking Pregnancy Weeks with an Ultrasound

An ultrasound scan helps determine how many weeks pregnant someone is. Healthcare providers usually schedule a dating ultrasound between week 6 and week 11 to measure the embryo’s size, which helps set a more precise timeline for the pregnancy.

If the embryo is small, a transvaginal ultrasound may replace the regular gel-on-abdomen method. This early scan gives valuable information for tracking both the baby’s growth and estimating a likely due date.

How to Keep Track of Pregnancy Weeks

Many people lose track of how many weeks pregnant they are as time goes on. One simple way to check is by counting from the first day of the last period. Using a pregnancy calculator can also help track weeks and important milestones. Marking the calendar or setting reminders can make it easier.

Can the Expected Birth Date Shift?

Sometimes, a due date changes as a pregnancy progresses. This often happens if a person has irregular periods or if new information comes from an early ultrasound. For example, a dating ultrasound may show a different stage of development than what doctors estimated from the last menstrual period. In these situations, doctors may adjust the due date to better match the baby’s actual growth.

Changes in fundal height, which is the distance from the top of the pubic bone to the top of the uterus, may also suggest a different timeframe. If that measurement is higher or lower than expected, doctors may reassess how far along the pregnancy is.