Calculate your estimated due date using your last menstrual period, conception date, or ultrasound measurements. Get a detailed pregnancy timeline with trimester information and important milestones.
There are several methods to calculate your estimated due date (EDD), each with varying levels of accuracy depending on the information available:
The most common method adds 280 days (40 weeks) to the first day of your last period. This follows Naegele's Rule, developed in the 1850s, which assumes a 28-day cycle with ovulation on day 14.
Formula: LMP date + 7 days - 3 months + 1 year
If you know the exact date of conception (such as with IVF or known ovulation date), add 266 days (38 weeks) to that date. This method is more accurate when conception timing is precisely known.
First-trimester ultrasounds (8-13 weeks) are the most accurate method, with precision within 3-5 days. The ultrasound measures the baby's size to determine gestational age. Your provider may adjust your due date if ultrasound dating differs significantly from LMP calculations.
Your due date is an estimate, not a guarantee. Here's what you need to know:
Despite careful calculations, only about 4-5% of babies are born on their exact due date. Most arrive within 2 weeks before or after the estimated date.
Babies born anywhere from 37 to 42 weeks are considered term. The safest time for delivery is 39-40 weeks (full term), when baby's organs are fully mature.
First-time mothers are more likely to deliver after their due date, with many going 41+ weeks. This is completely normal and not a cause for concern.
Your healthcare provider may adjust your due date based on early ultrasound measurements, especially if there's more than a 5-7 day difference from LMP calculations.
Medical professionals categorize pregnancies based on when baby is born relative to the due date:
Babies born before 37 weeks are considered premature and may need special medical care. The earlier the birth, the higher the risk of complications. Modern medicine has greatly improved outcomes for preterm babies.
While technically term, babies born at 37-38 weeks have slightly higher risks than those born at 39+ weeks. Unless medically necessary, it's best to wait for spontaneous labor.
This is the optimal time for delivery. Baby's brain, lungs, and liver are fully developed. Babies born during this window have the best health outcomes.
Pregnancies reaching 41 weeks are monitored more closely. Your provider may discuss induction options, though many healthy babies are born at this stage.
Pregnancies beyond 42 weeks carry increased risks. Most providers recommend induction between 41-42 weeks to reduce complications like placental insufficiency.
If your cycles are shorter or longer than 28 days, or vary significantly, LMP-based calculations may be less accurate. Women with irregular cycles should rely more heavily on ultrasound dating.
If you can't remember your last period date, were on birth control, or recently gave birth, ultrasound dating becomes essential for accurate due date calculation.
Twins and higher-order multiples typically arrive earlier. Average delivery is 35-36 weeks for twins, 32-33 weeks for triplets. Your provider will adjust expectations accordingly.
IVF pregnancies have the most accurate due dates since conception timing is precisely known. The calculation is based on embryo transfer date and embryo age at transfer.
As you approach your due date, here's what to expect:
If you reach your due date without going into labor, your provider will schedule more frequent check-ups, typically twice weekly. These visits include non-stress tests and amniotic fluid checks.
Your provider may offer a membrane sweep to encourage labor. This involves separating the amniotic sac from the cervix, which can trigger natural labor within 48 hours.
Most providers recommend induction between 41-42 weeks to reduce risks associated with post-term pregnancy, including placental aging and decreased amniotic fluid.
Watch for these signs that labor may be starting soon:
LMP-based calculators are accurate within 1-2 weeks for women with regular 28-day cycles. First-trimester ultrasounds are more accurate (within 3-5 days). Remember, only 4-5% of babies arrive on their exact due date.
Your healthcare provider will use an early ultrasound to estimate your due date. The earlier the ultrasound (ideally 8-13 weeks), the more accurate the dating will be.
Due dates are typically only adjusted in the first trimester based on ultrasound measurements. If there's a significant difference (more than 5-7 days) between ultrasound and LMP dating, your provider will use the ultrasound date.
Going past your due date is common, especially for first pregnancies. Your provider will monitor you more closely with twice-weekly appointments and may discuss induction options between 41-42 weeks.
Unless medically necessary, it's best to wait until at least 39 weeks for delivery. Babies born at 39-40 weeks have better outcomes as their organs, especially lungs and brain, are fully mature.
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