Printed on 3/17/2026
For informational purposes only. This is not medical advice.
This pregnancy due date calculator uses Naegele's rule to estimate your expected delivery date (EDD) from the first day of your last menstrual period (LMP). It adds 280 days (40 weeks) to the LMP date and shows your current [gestational age](/tools/gestational-age), trimester, and days remaining. Naegele's rule assumes a 28-day menstrual cycle with ovulation on day 14.
Formula: EDD = LMP + 280 days (Naegele's Rule)
Select the first day of your most recent period. This is the starting point for all pregnancy dating calculations, even though conception occurs about two weeks later.
The calculator adds 280 days (40 weeks) to your LMP date. This standard formula, developed in the 1800s, remains the foundation of pregnancy dating worldwide.
See your estimated due date, current gestational age in weeks and days, trimester, and countdown to delivery. Use this to plan prenatal visits and prepare for baby's arrival.
Newly pregnant couples
Calculate your due date immediately after a positive pregnancy test to begin planning prenatal care, share news with family, and prepare your timeline.
Obstetricians, midwives, nurses
Quickly establish dating at the first prenatal visit to schedule appropriate screening tests and plan the care timeline before ultrasound confirmation.
Couples planning conception
Calculate potential due dates based on planned conception timing to align pregnancy with work schedules, seasons, or personal preferences.
Employees planning leave
Determine your expected delivery window to plan maternity/paternity leave, project handoffs, and workplace coverage arrangements.
Second or third pregnancies
Track a new pregnancy alongside caring for older children, coordinating school schedules and sibling preparation with your due date.
Maternal-fetal medicine specialists
Establish baseline dating to plan intensified monitoring schedules, specialist consultations, and potential early delivery timing. Assess pre-pregnancy health with [BMI Calculator](/tools/bmi-calculator) and cardiovascular risk with [ASCVD Risk Calculator](/tools/ascvd-risk).
The first day of your last period is the most important date in pregnancy dating. Write it down or log it in an app as soon as you miss your period — memory fades quickly and accurate dating affects your entire care timeline.
While LMP-based dating is useful, a crown-rump length measurement between 7-13 weeks is accurate to within 5-7 days. If ultrasound dating differs from LMP by more than 7 days, clinicians will typically use the ultrasound date.
If your cycles are regularly longer than 28 days, add the extra days to your due date. For example, with a 35-day cycle, your actual ovulation is about 7 days later than assumed, so your due date is 7 days later than Naegele's rule predicts.
Your EDD is the middle of a delivery window, not a deadline. Only 5% of babies arrive on their exact due date. About 80% deliver between 38-42 weeks. Think of it as an 'estimate' rather than an appointment.
Key tests are time-sensitive: first-trimester screening at 11-13 weeks, anatomy scan at 18-22 weeks, glucose tolerance test at 24-28 weeks, and Group B Strep screening at 36-37 weeks. Know your gestational age to schedule correctly. For gestational diabetes management, track nutrition with [TDEE Calculator](/tools/tdee-calculator) and [Macro Calculator](/tools/macro-calculator).
Medical professionals count pregnancy in weeks and days (e.g., '28 weeks 4 days'), not months. This precision matters for clinical decisions. When asked 'how far along,' give weeks rather than months.
If you know your exact ovulation or conception date (from tracking or IVF), add 266 days to get your due date. This is more accurate than LMP for women who tracked ovulation precisely.
If your calculated due date differs significantly from ultrasound dating, ask your provider which date they're using and why. Consistent dating throughout pregnancy prevents confusion about timing decisions.
Twins average delivery at 36-37 weeks, triplets at 32-34 weeks. If you're carrying multiples, your 'due date' is a reference point, but expect delivery earlier than the standard 40 weeks. Increased nutritional needs require careful tracking with [Calorie Calculator](/tools/calorie-calculator) and [Protein Intake Calculator](/tools/protein-intake).
If you reach 41 weeks without delivery, your provider will discuss induction. True post-term pregnancy (beyond 42 weeks) carries increased risks and is rarely allowed to continue without intervention in modern obstetric care.
Naegele's rule dates to 1812 and remains the standard for initial pregnancy dating per ACOG guidelines. First-trimester ultrasound (crown-rump length) is accurate to ±5-7 days and is the gold standard when LMP is uncertain (Papageorghiou et al., Lancet 2014). Only 5% of births occur on the exact due date, with 80% occurring within ±11 days (Mongelli et al., BJOG 1996).
Your estimated due date (EDD) represents the date at which you will be 40 weeks pregnant, which is considered full term. However, only about 5% of babies are born on their exact due date. A normal, full-term delivery can occur anywhere between 37 and 42 weeks of gestation.
The calculator also shows your current gestational age in weeks and days, along with your trimester. First trimester (weeks 1–12) is a critical period of organ formation. Second trimester (weeks 13–27) involves rapid fetal growth and is when most women begin to feel fetal movement. Third trimester (weeks 28–40) involves final organ maturation and preparation for delivery.
Use this calculator early in pregnancy to estimate your due date and track your gestational progress. It is most appropriate for women with regular menstrual cycles who can reliably identify the first day of their last menstrual period.
The estimated due date is used to schedule prenatal visits, plan routine screening tests (e.g., first-trimester screening at 11–13 weeks, anatomy scan at 18–22 weeks, glucose tolerance test at 24–28 weeks), and guide clinical decisions about timing of delivery.
Naegele's rule assumes a 28-day menstrual cycle with ovulation occurring on day 14. For women with irregular cycles, longer or shorter cycles, or uncertain LMP dates, the estimate may be off by days to weeks. In these situations, first-trimester ultrasound dating (crown-rump length measurement between 7–13 weeks) is more accurate, with a margin of error of only ±5–7 days.
The calculator does not account for factors that can affect delivery timing, such as multiple gestation (twins/triplets tend to deliver earlier), maternal medical conditions (preeclampsia, gestational diabetes), or history of preterm or post-term delivery. It provides a statistical estimate — not a prediction of when labor will actually begin.
Disclaimer: This tool is for educational and informational purposes only. It is not a substitute for professional medical advice, diagnosis, or treatment. Always consult a qualified healthcare provider with questions about your health.
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