Calculate your estimated due date using Naegele's rule — see early, full, late, and post-term delivery windows, plus IVF-specific dating aligned with ACOG guidelines.
Estimate Based On:
This due date calculator accepts the first day of your last menstrual period (LMP) or your estimated conception date and returns your estimated due date (EDD), the key term boundaries recognized by ACOG, and a quick timeline of the first prenatal appointment window. It uses Naegele's rule as the primary calculation method — LMP minus 3 months plus 7 days — which is mathematically identical to adding 280 days to LMP. The calculator also accepts IVF transfer dates for patients who underwent assisted reproduction. For the most clinically accurate EDD in situations of uncertain LMP or irregular cycles, early ultrasound (8–13 weeks, using crown-rump length) is the gold standard per ACOG guidelines.
The due date, also known as the estimated date of confinement, is an estimation of when a pregnant woman will deliver her baby. While the due date is often estimated as a single date, it can be helpful to consider a range of due dates, since only 4% of births occur on the estimated due date.
Due dates can be estimated using a number of different methods, including the last menstrual period, ultrasound, conception date, and IVF transfer date.
The default method bases the calculation on a woman's last menstrual period, under the assumption that childbirth on average occurs at a gestational age of 280 days, or 40 weeks. In terms of gestational age, pregnancies typically last between 37 and 42 weeks, with 40 weeks often being used as an estimate.
Estimating due date based on ultrasound involves using soundwaves to look inside the body and compare fetal growth to typical growth rates. It is simple, has no known risk, and can be accurate early in pregnancy.
Similar to using LMP, with about a two-week difference based on the timing between the last menstrual period and the date of conception.
Generally more precise since the exact transfer date is known. Uses the average gestational age of 40 weeks from LMP, with adjustments for 3-day or 5-day embryo transfer.
Enter the first day of your LMP — or your conception date if you know it — and tap calculate. The result is your estimated due date along with the calendar windows for early term (37–38 weeks 6 days), full term (39–40 weeks 6 days), late term (41–41 weeks 6 days), and post-term (42 weeks and beyond). The EDD is a statistical midpoint: only about 5% of babies are born exactly on their due date, with most arriving within two weeks of it. If you're past 40 weeks, don't panic — being "late" is common and your provider monitors the pregnancy closely in those final days. Delivery before 37 weeks is preterm; your provider will discuss induction or c-section only if medical criteria support it.
Naegele's rule, the standard formula endorsed by ACOG:
EDD = LMP date − 3 months + 7 days
This is equivalent to adding 280 days (40 weeks) to the LMP date.
For an LMP of January 1, 2026: subtract 3 months → October 1, 2025; add 7 days → October 8, 2026 EDD. If conception date is entered instead, the calculator adds 14 days (average LMP-to-ovulation interval) to produce LMP equivalent before applying Naegele's rule.
Franz Karl Naegele published his rule in 1812, and it remains the international obstetric standard because it does one thing very well: it translates a single known date (LMP) into a reliable population-level prediction of delivery timing. The rule assumes a 28-day cycle with ovulation at day 14 — accurate for many, not all, women — and projects 40 weeks as the average gestation. Large-scale studies on spontaneous labor onset confirm that the median delivery does cluster around 40 weeks from LMP, validating the formula despite its simplistic cycle-length assumption. ACOG continues to endorse Naegele's rule as the baseline calculation, with ultrasound used to refine it when LMP is uncertain. The formula hasn't changed because pregnancy biology hasn't changed — average human gestation is still approximately 280 days.
The LMP-based due date is only as accurate as the underlying assumption that you ovulate on day 14 of a 28-day cycle. For women with cycles consistently longer, shorter, or more variable than that, the LMP method can be off by a week or more. This is why ACOG recommends that when an ultrasound performed between 8 and 13 weeks 6 days disagrees with the LMP date by more than 5–7 days, the ultrasound-derived date should be used for all subsequent dating. Ultrasound dating in this window uses the crown-rump length (CRL) — the distance from top of the embryo's head to its bottom — which correlates precisely with gestational age because embryos of the same age are almost identical in size in early pregnancy, before nutritional and genetic variation in growth becomes a factor. After the first trimester, ultrasound dating becomes progressively less accurate because fetal size starts to diverge based on individual growth factors. Bottom line: your LMP-derived EDD is a good starting number; the 8–12 week ultrasound is the more precise one.
Not all deliveries at "term" are equivalent. ACOG revised its terminology in 2013 to distinguish four categories within what was previously just called "term":
Your EDD falls exactly at the boundary of full term and late term (week 40). This refined terminology exists because outcome data showed that early-term babies (37–38 weeks) have measurably higher rates of respiratory distress, NICU admission, and neurodevelopmental differences than babies born at 39–40 weeks — which is why non-medically indicated inductions or c-sections before 39 weeks are not recommended without clinical justification.
For pregnancies conceived through in vitro fertilization, the calculation differs because the conception event (embryo transfer) is a known date rather than an estimate. For a day-5 embryo transfer, the equivalent LMP date is the transfer date minus 17 days (12 days for the ovulation-to-LMP gap, plus 5 days for blastocyst age). The EDD is then calculated by adding 280 days to that equivalent LMP, or more practically: transfer date + 263 days for a day-5 transfer. Clinics typically provide the EDD directly, but patients can verify this with the calculator. IVF pregnancies are dated with high precision because the exact developmental age is known, eliminating the uncertainty of ovulation timing that affects natural-conception dating.
Going past 40 weeks is normal and common — statistically, about 60–70% of first-time pregnancies extend past the due date, with a median delivery closer to 41 weeks than 40. What changes at and after 40 weeks is surveillance: providers typically increase monitoring through non-stress tests (NST) and biophysical profiles (BPP) to assess placental function and fetal well-being. The placenta begins to age and function less efficiently after 41–42 weeks, which is why ACOG guidelines discuss induction of labor at or before 42 weeks in uncomplicated pregnancies. Going a few days past the EDD with a well-monitored, healthy pregnancy is not a crisis; going significantly past 42 weeks without medical oversight is a clinical concern.
LMP accuracy is the dominant variable — an uncertain or recalled LMP can shift the EDD by a week or more. Cycle length and regularity determine how well the 28-day assumption holds: women with 35-day cycles consistently ovulate a week later, shifting the true EDD a week later than Naegele's formula suggests. Early ultrasound (8–13 weeks) is the strongest corrective factor when LMP is uncertain. For IVF patients, the transfer date and embryo age (day 3 vs. day 5) provide a directly calculable EDD with minimal uncertainty. Twin and higher-order multiples pregnancies often have different milestone timelines — providers typically target earlier delivery to reduce risk.
Rachel has an LMP of October 15, 2025. Applying Naegele's rule: October 15 − 3 months = July 15; + 7 days = July 22, 2026 EDD. Full-term window: June 23 (39 weeks) to July 21 (40 weeks 6 days). Rachel's first prenatal appointment would typically be scheduled around weeks 8–10, between December 10–24, 2025.
Jenna underwent a day-5 IVF embryo transfer on April 2, 2026. Equivalent LMP: April 2 − 17 days = March 16, 2026. EDD: March 16 + 280 days = December 21, 2026. Jenna's reproductive endocrinologist provided the same date — confirming the formula works — and scheduled her first OB appointment after the 8-week ultrasound on May 11.
Record your LMP as soon as you begin trying to conceive — it's the most commonly needed date across all pregnancy calculations, and relying on memory after a positive test often leads to uncertainty.
Attend your first-trimester ultrasound (ideally 8–10 weeks) to confirm or adjust the LMP-derived EDD; this is the most impactful single appointment for due-date accuracy.
Don't fixate too narrowly on the exact EDD — the full-term window of 39–40 weeks 6 days is the real target range; labor can begin any time in the weeks around it.
If LMP and ultrasound disagree, always use the ultrasound-derived EDD going forward — your entire prenatal care schedule, test windows, and induction discussions are all anchored to that date.
For IVF pregnancies, provide your embryo transfer date and embryo age (day 3 or day 5) to the calculator for the most precise EDD possible from the start.
Use the term-category breakdown (early, full, late, post-term) to understand why your provider may discuss timing options at different points — not all days after 37 weeks carry equal risk.
Use Naegele's rule: take the first day of your last menstrual period, subtract 3 months, and add 7 days. This gives your estimated due date (EDD). Alternatively, add 280 days (40 weeks) to your LMP date. The ACOG endorses this as the standard calculation method.
Enter your LMP into the due date calculator — it applies Naegele's rule automatically and returns your EDD within seconds. The result also shows your full-term window and key prenatal appointment timing.
LMP-based calculators are accurate within about a week for women with regular 28-day cycles. For irregular cycles, early ultrasound at 8–12 weeks using crown-rump length measurement is more accurate and ACOG recommends it supersede the LMP date when the two differ by more than 5–7 days.
Naegele's rule is the standard obstetric formula for estimating due date: EDD = LMP − 3 months + 7 days (equivalent to LMP + 280 days). Published in 1812, it remains the international standard endorsed by ACOG for calculating estimated delivery dates.
Yes — the majority of first-time pregnancies extend past 40 weeks, with median delivery closer to 41 weeks. Delivery between 39 and 42 weeks is considered normal term. After 41 weeks, providers increase monitoring; most recommend induction by 41–42 weeks in uncomplicated pregnancies.
According to ACOG, full term is 39 weeks 0 days through 40 weeks 6 days — the optimal delivery window. Early term (37–38+6 weeks) and late term (41–41+6 weeks) are recognized as distinct periods with different risk profiles.
For a day-5 embryo transfer, subtract 17 days from the transfer date to get the equivalent LMP, then add 280 days for the EDD (or add 263 days directly from the transfer date). IVF pregnancies have precise conception timing, making their EDDs among the most accurate calculated dates available.
Brief disclaimer: This calculator provides educational due date estimates using Naegele's rule and standard obstetric conventions. Results are for informational purposes only and do not constitute medical advice. Actual delivery timing varies — only about 4–5% of births occur on the estimated due date. Early ultrasound dating (8–13 weeks) provides the most clinically accurate EDD. Always consult your OB-GYN or certified nurse-midwife for personalized prenatal care and delivery planning.