Pregnancy Due Date Calculator

Classic Naegele's rule assumes a 28-day menstrual cycle where ovulation occurs on day 14 (LMP + 280 days). If your cycle is longer (e.g., 32 days), ovulation is delayed by 4 days, shifting your EDD forward by 4 days. Conversely, in shorter cycles (e.g., 24 days), ovulation occurs earlier, moving the EDD 4 days earlier.

Gestational age is calculated from the first day of the Last Menstrual Period (LMP), which includes approximately two weeks before conception occurs. Embryonic (or conceptional) age measures the actual biological age of the developing fetus starting from fertilization, making it roughly two weeks less than gestational age.

The estimated due date represents the 40-week median mark, but normal physiological full-term delivery spans a wide biological window between 37 weeks (early term) and 42 weeks (post term). Spontaneous onset of labor depends on cervical maturation, fetal adrenal steroid signaling, and oxytocin receptor density rather than a rigid calendar date.

According to American College of Obstetricians and Gynecologists (ACOG) guidelines, if an accurate first-trimester ultrasound measurement of Crown-Rump Length (CRL) differs from the LMP-derived date by more than 5 days (up to 8 6/7 weeks) or more than 7 days (9 to 13 6/7 weeks), the clinical due date is officially re-dated to the ultrasound estimate.

Yes. Conception typically occurs on or near the day of ovulation, which occurs approximately 14 days before the next anticipated menses. In this calculator, estimated conception is computed as LMP + 14 days + (cycle length - 28 days), providing an accurate biological conception milestone.