Multi-Method Clinical Estimation

Due Date Calculator

Calculate your estimated arrival date using your last menstrual period, known conception date, or first-trimester ultrasound biometric measurements.

Multi-Method Clinical Dating Evidence-Based Estimation

Due Date Calculator

Estimate your baby's arrival date using your last menstrual period, date of conception, or ultrasound scan results.

Range: 20–45 days

Calibrates estimated ovulation relative to standard 28-day cycle length.

The Science of Due Date Estimation

A calculated due date (Estimated Date of Delivery, or EDD) marks the completion of 40 gestational weeks (280 days from the LMP). However, according to the American College of Obstetricians and Gynecologists (ACOG), spontaneous human labor is a natural biological spectrum spanning weeks 37 through 42.

Why Do Different Methods Produce Different Due Dates?

  • LMP Method: Assumes a standard 28-day cycle with ovulation on day 14. If your cycle is 35 days, ovulation occurred around day 21, shifting your true due date 7 days later.
  • Conception Method: Calculates directly from the day the ovum was fertilized, bypassing menstrual cycle assumptions.
  • First-Trimester Ultrasound: Measures the embryo's Crown-Rump Length (CRL). In early pregnancy, biological variation is minimal, making early ultrasound dating accurate to within ±5 to 7 days.

A Due Date is an Estimate, Not an Expiration Date

Only about 4 to 5 percent of women deliver on their exact calculated due date. Approximately 80% deliver between 37 weeks 0 days and 41 weeks 6 days. Your obstetrician or midwife will reconcile your menstrual history with ultrasound findings to establish your official clinical EDD.

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