Due Date Calculator

ACOG's convention: due date = LMP + 280 days (40 weeks), which assumes a 28-day cycle with ovulation on day 14 (ACOG). The cycle-length option is a conventional rough calendar adjustment, not a guideline recommendation: it assumes ovulation about 14 days before your next period, so the due date moves by (cycle length minus 28) days and the week count starts from that adjusted date. It cannot be precise, especially with irregular cycles. A conception date uses 266 days (280 minus 14). ACOG notes LMP dating is often inaccurate and ultrasound dating can replace it. Trimesters follow ACOG (source). The conception-date option adds 14 days to count gestational age from the LMP. Always confirm via ultrasound with your OB-GYN.