Most pregnancies last around 38 weeks from conception. Typically women ovulate about two weeks after their menstrual cycle starts, so the best way to estimate your due date is to count 40 weeks, or 280 days, from the first day of your last menstrual period.
Another way to do it is to subtract three months from the first day of your last period and add seven days. So if your last period started on April 11, you’d count back three months to January 11 and then add seven days, which means your due date would be January 18.
This is how your doctor will estimate your due date — and it’s a pretty solid target. But remember: It’s just as normal to deliver a week or two before or after.
You have several options for determining your conception date:
- An ultrasound is the most accurate way to see how far along your pregnancy is. Ultrasounds provide a detailed look at your baby’s development and will give you a good estimate of how far along your pregnancy is.
- An online pregnancy calculator can give an estimate of when you conceived based on when your last period was. This method is not as accurate as a confirmation ultrasound.
We offer free ultrasounds at our pregnancy center. Our medical professionals are trained in limited obstetrical ultrasound and provide medical services under the direction and supervision of a licensed physician.
How to Know When You Conceived
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. Ovulation usually occurs about two weeks after your menstrual period and lasts for two or three days.
However, 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 just on your body cycles can be difficult.
You can also simply try to determine the last time you had sexual intercourse, but 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. All of these factors can make it hard to know when exactly you conceived.
This is why a pregnancy confirmation ultrasound is the best way to know how far along your pregnancy is and to determine when you conceived. Pregnancy ultrasounds look directly at the development of your growing baby to determine its age and when you likely conceived. This method is much more accurate than date-based calculation.
The Pregnancy Conception Calculator estimates the date of conception based on the expected due date of the pregnancy, last period date, or ultrasound date. The date of conception is the day on which a person's baby is conceived. The calculator also estimates a possible range of days during which sexual intercourse might have led to conception based on sperm being viable for 3-5 days within a woman's body.
When Did I Conceive?
When exactly did I get pregnant? Many women often ask this question when trying to figure out the exact day their pregnancy began. Often, gestational age, or the age of the baby, is calculated from the first day of the mother's last menstrual period. However, in reality, the baby was not conceived until ovulation and the fertilization of the egg, which usually happens at least 10 days after the first day of the mother's menstrual period.
Because there are many factors surrounding conception, it is difficult to pinpoint an exact date of conception. This calculator helps to estimate the date range of real conception and a possible range of days during which sexual intercourse might have led to conception. There are a few methods that can be used to estimate the conception dates:
Last Menstrual Period
Conception usually occurs around 11-21 days after the first day of the last period of a woman who has a regular period. The estimation of conception date is based on this, but is rarely ever exact since it is difficult to know exactly when ovulation occurs. Estimating conception date can also be more difficult for women who have irregular periods, or for those who don't remember the first day of their last period. In cases like these, one of the more accurate ways to estimate gestational age is through the use of an ultrasound.
Due Date
An estimated due date, usually based on a sonogram, is typically obtained from a healthcare provider during a prenatal visit. Based on this due date, a range of possible conception dates can be calculated.
Ultrasound
An ultrasound, on a basic level, uses sound waves to create images of internal body structures. An ultrasound used in the context of examining the progress of the fetus in pregnant women is referred to as an "obstetric ultrasound." This is done in real-time and is a fairly standard procedure that is part of prenatal care in many countries, as it can provide information about the health of the mother and embryo/fetus, as well as the overall progress and timing of the pregnancy. Ultrasounds can be used to measure a fetus as early as five or six weeks following the mother's last menstrual period. It is a more accurate measure in early pregnancy than it is in later stages. Ultrasound can be used in conjunction with estimates based on the last menstrual period to determine a more accurate gestational age.