💑 Conception Tool
Pregnancy Conception Calculator
Estimate when conception likely occurred and your fertile window using your due date or last menstrual period.
How conception dating works
From due date – Pregnancy lasts approximately 266 days (38 weeks) from conception. Subtract 266 days from your due date to estimate the conception day.
From last menstrual period (LMP) – Ovulation usually occurs 14 days before your next period. For a 28‑day cycle, ovulation = LMP + 14 days. Conception occurs within 24 hours of ovulation.
Conception window – Because sperm can live up to 5 days and the egg survives 24 hours, the fertile window spans several days. Our calculator shows the most likely single day (±1 day).
⚠️ This tool provides estimates only. Ultrasound dating in early pregnancy is the most accurate way to determine gestational age and conception.