Pregnancy Due Date Calculator

Your estimated due date (EDD) is an approximate date, around 40 weeks from the first day of your last menstrual period, by which your baby may arrive. It is genuinely an estimate: only about 1 in 20 babies is born on the exact estimated date, and a healthy, full-term birth can occur across a range of roughly two weeks on either side.

This calculator uses the date of your last period, which assumes a regular 28-day cycle with ovulation around day 14. If your cycles are consistently longer, shorter, or irregular, the last-period method may be less accurate for you, and your healthcare provider may adjust your dating accordingly.

A first-trimester ultrasound typically dates a pregnancy more accurately than the last-period method, and providers often use it to confirm or revise the due date. Use this estimate to plan and to know roughly where you are in the pregnancy — not as a fixed appointment. Your provider's dating always takes precedence over any calculator.

Last-period dating tends to be most accurate for people with regular, roughly 28-day cycles who are certain of the first day of their last period. In that situation the estimate lines up reasonably well with early-ultrasound dating for most pregnancies.

It may be less accurate if your cycles are irregular, longer or shorter than 28 days, if you conceived shortly after stopping hormonal contraception, or if you are unsure of your last period's start date. In these situations the estimate can be off by a week or more, and clinical dating — usually a first-trimester ultrasound — is used instead. Whatever this calculator shows, your provider's dating is the one to follow for scheduling and decisions about your care.

Formula. We apply Naegele's Rule: the estimated due date is the first day of your last menstrual period plus 280 days (40 weeks). This is the standard estimation method endorsed by the American College of Obstetricians and Gynecologists (ACOG).

What it assumes. Naegele's Rule assumes a standard 28-day cycle. Because cycle length and the exact timing of ovulation vary between people, the method has known limits, which is why ACOG notes that first-trimester ultrasound dating is considered more accurate when available.

Confidence. This is the lowest-confidence calculator on the site, and deliberately so. Individual cycle variation and the imprecision of last-period dating mean the Confidence Meter shows only a partial fill — a clear, honest signal that the due date is an estimate, not a prediction.