Are you pregnant but not sure exactly when you conceived? Ultrasound is the most accurate way to determine how far along you are in your pregnancy. 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. Schedule an appointment.
Please select the first day of your last period:
Your last period date:
How to Know When You Conceived
In general, there are a few ways to determine your conception date. No method is 100% accurate, but some are more reliable than others.
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. Some women simply 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 totally accurate either. Conception is a process and takes time, and a man’s sperm can actually 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 have had more than one partner during the time 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 best way to determine your conception date is with a pregnancy confirmation ultrasound. A pregnancy confirmation ultrasound may help you determine your conception date. Early pregnancy ultrasounds can determine the age of your growing baby and when you likely conceived. We provide free limited obstetric ultrasound to confirm pregnancy. This method of determining your conception date can be more accurate than date-based calculation, especially for women with irregular periods or who don’t know their last menstrual period date.
LeAnn Robertson, RN
The content on this page has been reviewed by our Registered Nurse: LeAnn Robertson.