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When Did I Conceive?

Updated: Jul 15, 2022

Are you pregnant but not sure exactly when you conceived? Online due date calculators can not give you an accurate measurement of how far along you are and pregnancy tests, while far more accurate than they used to be, are an indicator of pregnancy, not a confirmation.

An ultrasound will measure how many weeks pregnant you are, your approximate conception date, and due date. Ultrasound exams provide images and include various measurements of your developing baby that can help estimate how many weeks pregnant you are and your approximate conception date.

We provide referrals for free ultrasounds if you have a positive pregnancy test at our center.


There are a few ways to have a general idea of your conception date before an ultrasound.


The first way to find out your conception date is to determine when you were last ovulating. In general, women can only conceive when they are ovulating — that is, when their ovaries release a new egg into their fallopian tubes for fertilization. That means you can use your ovulation dates to try to determine when you became pregnant.

Ovulation usually occurs about two weeks after your menstrual period and lasts for two or three days. This means you can sometimes determine when you conceived based on your ovulation cycles — simply determine when your last menstrual period was, and add approximately two weeks.

However, this method isn’t always accurate. Not all women have the same cycles of menstruation and ovulation. Some women’s menstrual cycles are irregular, others have ovulation periods closer to or further from their menstrual period, and some women aren’t sure when their last period was. In other words, calculating conception based only on your body cycles can be difficult.


Another way to learn your conception date is to try to determine the last time you had sexual intercourse. Unfortunately, this method isn’t accurate either. Conception is a process and takes time, and a man’s sperm can stay alive inside your body for up to a week after sex.

This can make it difficult to determine when you conceived, especially if you had more than one partner when you ovulated. Also, remember that you could become pregnant even if you or your partner used birth control since no method of birth control is 100% effective at preventing pregnancy.


The only 100% accurate way to determine your conception date is with a pregnancy confirmation ultrasound. A pregnancy confirmation ultrasound can help you determine approximately when you conceived and the age of your growing baby.

We provide referrals for free ultrasounds so you can confirm your pregnancy. This method of determining your conception date can be more accurate than date-based calculation, especially for women with irregular periods or women who don’t know their last menstrual period date.

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