Due Date Calculator Choose from a variety of ways to predict your due date

First day of last period

For upon |Most pregnancies last around 40 weeks (or 38 weeks from conception), so typically 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 (LMP). 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.

Conception date

Calculating your due date based on the first day of your last period works well for women who have a relatively regular menstrual cycle. But if your cycle is irregular, the LMP method may not work for you. Because a reliable estimated date of delivery (EDD) is important, you and your practitioner can use your conception date instead if you remember it. Just add 266 days to get your estimated due date.

IVF transfer date

There are more than 250,000 assisted reproductive technology cycles performed each year in the United States, resulting in about 77,000 or more babies born a year, according to the Centers for Disease Control and Prevention (CDC). If you are part of the growing tribe of IVF moms, you can calculate your due date more precisely using your IVF transfer date. 

Ultrasound scan

Even if you can’t pinpoint when you conceived, forget the day of your last menstrual period or aren’t sure when ovulation occurred, other clues can help you and your practitioner determine your due date at your first prenatal appointment, including:

• An early ultrasound, which can more accurately date the pregnancy. Just be aware, however, that not all women get an early ultrasound. Some practitioners perform them routinely, but others only recommend one if your periods are irregular, you’re 35 or older, you have a history of miscarriages or pregnancy complications, or the due date can’t be determined based on your physical exam and LMP.

• Pregnancy milestones such as the first time the baby’s heartbeat is heard (around week 9 or 10, though it can vary) and when you first feel fetal movement (on average between 18 and 22 weeks, but it can be earlier or later), can give clues as to whether your due date is accurate.
• Your fundal height, which is the measurement from your pubic bone to the top of your uterus, is checked by your practitioner at each prenatal visit and helps confirm your due date.
• The size of your uterus, which will be noted when your initial internal pregnancy exam is performed, can also be a factor in pinpointing the EDD.

Can I plan my due date?

Whether you’re trying to avoid being very pregnant in the middle of summer or are a teacher who wants to maximize time off with your little one, you can try to time when you conceive in order to “plan” your due date. But even if you’re one of the lucky ones who’s able to get pregnant when she really wants to, just remember that you probably won’t be able to map out exactly when you’ll give birth to the day (or even the week or month!). 

Can my due date change?

Yes, your due date can change. While it’s definitely not a reason to worry, your doctor may change your due date for a number of reasons as your pregnancy progresses. It may be that your periods are irregular and your early ultrasound dating was off, or that your first ultrasound was in the second trimester. It could also be because your fundal height is abnormal, or your levels of alpha-fetoprotein (AFP), a protein made by the baby, are outside the usual range. Talk to your practitioner if you have any questions or concerns.

The article was originally published here.