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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). You could also subtract three months from the first day of your last period and add seven days.
The first day of your LMP is how most health care providers estimate a baby’s due date. But remember, it’s only an estimated due date, not a deadline for your baby to arrive. Just 4 percent of babies are born on their estimated due date.
If you’ve been tracking ovulation symptoms or have been using ovulation test strips, then you may be able to use your conception date to calculate your pregnancy due date. Just add 266 days to get your estimated due date (or select “Conception Date” from the menu above, and let our Due Date Calculator do the math for you).
If you conceived through in vitro fertilization (IVF), you can calculate your due date using your IVF transfer date. Most embryo transfers occur either three days or five days after egg retrieval and fertilization. If you had a day-three transfer, count 263 days from the transfer date to calculate your due date, and if you had a day-five transfer, count 261 days. (Or select “IVF” from the menu above.)
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.
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!).
Still, you can try our Ovulation Calculator, which uses the date of your last menstrual period and your typical cycle length to discover the days you’re most likely to be fertile and increase your chances of conceiving.
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 you have irregular periods 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.
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