Pregnancy Due Date Calculator

The calculator normalizes each dating method into an estimated gestational start date and a 40w0d estimated due date. For last menstrual period dating, it uses 280 days from LMP and adjusts for cycle lengths above or below 28 days. For conception dating, it adds 266 days to the conception date.

IVF mode uses the embryo transfer date and embryo age. Ultrasound mode uses the scan date and measured gestational age to estimate the remaining days to 40w0d. Reverse mode starts from a known due date and works backward to estimate LMP and conception timing.

All date math uses calendar-day calculations. The output should be treated as a planning estimate until confirmed by a qualified prenatal care team.

1) Which Dating Method Should You Use?

The best input depends on what information is reliable. If the first day of the last menstrual period is known and cycles are regular, LMP dating is a common starting point. If ovulation was tracked, conception dating may be more specific. For IVF pregnancies, embryo transfer records are usually the most relevant starting point.

Ultrasound can confirm or revise dating, especially early in pregnancy. ACOG notes that first-trimester ultrasound is the most accurate method to establish or confirm gestational age. Later scans can still help, but they have wider dating uncertainty.

2) Understanding Gestational Age

Gestational age counts from the estimated first day of the last menstrual period, not from conception. This is why conception usually occurs at about 2w0d gestational age in a typical 28-day cycle. The calculator reports both estimated conception date and gestational age so the two timelines are not confused.

A due date is an estimated date of delivery. Many pregnancies deliver before or after the exact date. Prenatal care teams use the assigned EDD to schedule screening windows, interpret fetal growth, and plan follow-up.

3) When to Trust Clinical Dating Over a Calculator

Use clinician dating when it differs from a simple calendar estimate. Your care team may have access to ultrasound measurements, IVF documentation, cycle history, exam findings, or prior records that make the official EDD more reliable than a standalone calculator.

Contact your healthcare professional promptly for bleeding, severe pain, decreased fetal movement later in pregnancy, persistent vomiting, high blood pressure symptoms, or any urgent concern. This page is a planning tool, not a triage tool.

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