Predict how many weeks pregnant you are

Ultrasound: At some point during your pregnancy, you will likely have an ultrasound scan. This enables your healthcare provider to check on fetal growth and monitor other development milestones; it also provides the most accurate estimate for how many weeks pregnant you are and what your due date will be. This method is the most reliable, and particularly useful if you don't know the date of your last period or if your menstrual cycles are irregular.

When figuring out how far along you are, it can be confusing that the weeks of pregnancy are not the same as the gestational age of the baby. Remember, conception most likely occurred about 14 days into your last cycle, whereas pregnancy is calculated from the beginning of that cycle, so there's a two-week difference.

For example, when you're six weeks pregnant, your baby's gestational age is only four weeks. During your prenatal checkups, your healthcare provider will monitor how far along you are. Don't be surprised, though, if your provider gives you a slightly different due date than the one you calculated.

Also, most babies don't arrive exactly on their due date. Every pregnancy is unique, and only a small percentage of babies are born right on time.

Babies are typically born between weeks 38 and 42, and it's totally normal for your baby to arrive any time during this window. If your baby is born pre-term , your doctor will be able to advise you on any extra care your baby might need. Page last reviewed: 29 April Next review due: 29 April Home Pregnancy Finding out you're pregnant Back to Finding out you're pregnant. Due date calculator. The calculator on this page can help you work out when you might expect your baby to arrive.

Do I need a dating ultrasound? Calculate using milestones Historically, the first heartbeat and first movement are used to get a sense of how far along you are or the age of the fetus, but these forms of measurement are now considered outdated.

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First, calculate current gestation using one of the other methods, then go to this section and choose past or future date. Date at future or past gestation: Use to calculate the date at a specific gestation enter in weeks. First, calculate current gestation using one of the other methods, then go to this section and choose a gestational age.