How Accurate Is a Due Date?
Your Estimated Due Date (EDD) is a midpoint estimate — not a precise prediction. Here is what science says about how accurate it really is.
The Statistics on Due Date Accuracy
Multiple large studies of birth timing show that the EDD functions as a midpoint of a normal distribution, not a precise target. A 2013 study published in Human Reproduction found that the average time from ovulation to birth is 268 days — but with a standard deviation of 9.6 days, meaning most births fall within a roughly 3-week window on either side.
Only about 5% of women give birth on their exact EDD. About 70% deliver within 10 days. About 90% deliver within 2 weeks of the EDD. The remaining 10% give birth more than 2 weeks before or after.
Accuracy by Dating Method
| Method | Typical Accuracy | Best Condition |
|---|---|---|
| IVF / Embryo Transfer | ±1–3 days | Known embryo age |
| First-trimester CRL Ultrasound | ±5 days | 8–14 weeks |
| LMP (regular cycles) | ±7–14 days | 28-day cycle, certain LMP |
| LMP (irregular cycles) | ±2–4 weeks | Irregular or uncertain LMP |
| Second-trimester ultrasound | ±2–3 weeks | 14–28 weeks |
| Third-trimester ultrasound | ±3–4 weeks | After 28 weeks |
What Your Due Date Really Means
Think of your due date as the midpoint of a normal birth window, not a deadline. ACOG defines full-term pregnancy as 39 weeks 0 days through 40 weeks 6 days. Babies born at 37–38 weeks 6 days are "early term." Babies born at 41 weeks through 41 weeks 6 days are "late term."
Knowing your EDD helps your healthcare team monitor your pregnancy milestones, schedule appropriate screenings, and plan for birth. It is not meant to cause anxiety — only about 1 in 20 babies arrives exactly on the predicted date.
Frequently Asked Questions
Common questions answered by our medical team