Calculate your pregnancy due date from LMP, conception date, IVF transfer, or ultrasound. Tracks trimester milestones & US prenatal schedule | Calculator4U
Estimate your baby's delivery date.
The Due Date Calculator estimates your baby's expected arrival using Naegele's Rule, the standard medical method for calculating the estimated date of delivery (EDD). A due date calculator determines your personalized target date by computing exactly 40 weeks—the average length of human gestation from the start of your last period—so you can plan prenatal appointments, prepare your hospital bag, and track every development from first heartbeat to full term.
Your estimated due date is not a deadline—it is the midpoint of a normal delivery window. Only 4% to 5% of babies are born on their exact due date. A full-term pregnancy ranges from 37 to 42 weeks, and most healthy babies arrive within two weeks on either side of the EDD. Your ACOG-certified OB-GYN or certified nurse-midwife (CNM) will confirm your due date at your first prenatal visit, typically using an early ultrasound between 8 and 14 weeks. Your healthcare provider may adjust your due date based on ultrasound measurements, especially if your menstrual cycle is irregular.
Pregnancy is typically divided into three trimesters, each with distinct developmental changes. The first trimester involves foundational organ formation, the second trimester brings rapid skeletal growth and visible movement, and the third trimester focuses heavily on vital brain development, lung maturation, and weight gain in preparation for birth.
This formula assumes a baseline 28-day cycle with ovulation occurring on day 14. If yours differs, apply the cycle adjustment:
Example: An LMP of January 1, 2025, with a 30-day cycle results in an EDD of October 13, 2025 (280 days + 2 extra days). Without cycle adjustment, the raw baseline EDD would incorrectly calculate as October 11, 2025.
| Trimester / Stage | Weeks | Key Developments |
|---|---|---|
| First Trimester | 1-12 | Organ formation, primary structures lock in, embryonic heartbeat detectable. |
| Second Trimester | 13-27 | Fetal movement felt (quickening), anatomical gender visible, phase of rapid growth. |
| Third Trimester | 28-40 | Accelerated brain development, lung tissues mature, critical sub-cutaneous weight gain. |
| Early Term | 37-38 | Baby's structural development is complete; entering the physiological delivery zone. |
| Full / Late Term | 39-41 | The optimal delivery window for newborn health outcomes. |
The American College of Obstetricians and Gynecologists (ACOG) recommends scheduling your first prenatal visit at 8–10 weeks. Standard healthcare protocols include 12–14 total checkups for a low-risk singleton pregnancy. Your anatomy scan (the 20-week ultrasound) serves as the key milestone where physiological features are reviewed and dating metrics can be refined. Later, a Group B Strep screening occurs at 36 weeks, after which your clinical visits shift to a weekly frequency until your delivery date.
Naegele's Rule: LMP + 280 days (40 weeks). Assumes 28-day cycle, ovulation day 14. Adjust by adding/subtracting days if your cycle differs. Conception date: +266 days. IVF day-5 blastocyst: subtract 5 days from transfer, add 280. First-trimester ultrasound (before week 14) is the most accurate method per ACOG 2026.
LMP-based: accurate within 1–2 weeks for regular cycles. Only 4–5% of US babies arrive on exact EDD. First-trimester ultrasound is the gold standard — margin of error just ±5–7 days. After 20 weeks, accuracy drops to ±2–3 weeks. ACOG recommends confirming with early ultrasound.
Days since first day of LMP ÷ 7 = gestational age in weeks. At a positive pregnancy test you are typically already 4–5 weeks pregnant. Conception occurs ~day 14 of a 28-day cycle (2 weeks after LMP). Don't remember LMP? An early ultrasound can establish gestational age.
Yes. Day-5 blastocyst: transfer date − 5 days = equivalent LMP, then + 280 days. Day-3 embryo: − 3 days. IVF EDD calculations are highly reliable because fertilisation date is precisely known — more accurate than LMP-based methods for natural conception.
Gestational age is counted from LMP and is used by all US prenatal providers. Fetal age (embryonic age) is counted from conception — approximately 2 weeks less. All US ultrasounds, charts, and ACOG guidelines use gestational age, not fetal age.
ACOG recommends 8–10 weeks for your first prenatal visit. It includes a dating ultrasound, blood tests, and blood pressure check. High-risk pregnancies may be seen at 6–7 weeks when heartbeat is first detectable.
ACOG defines full term as 39w 0d to 40w 6d. Early term = 37–38 weeks (viable but not optimal). Late term = 41 weeks. Post-term = 42+ weeks — US providers typically recommend induction due to placenta aging. Safest delivery window: 39–40 weeks.