Estimate when conception most likely occurred.
Curious about when you conceived? This calculator works backwards from your due date, baby's birth date, or an ultrasound scan to estimate the most likely conception window. It uses established obstetric guidelines — a 280-day gestational period and an average ovulation on day 14 of a 28-day cycle — to pinpoint the 11-day window when fertilisation most likely occurred.
Whether you want to settle a birthday debate, track a medical timeline, or simply satisfy your curiosity, the tool runs entirely in your browser with nothing stored or sent anywhere.
Three Input Methods
Calculate from a due date, actual birth date, or ultrasound scan with gestational age.
Conception Window
Provides the full 11-day window (days 11–21 of the cycle) when fertilisation most likely happened.
Key Dates at a Glance
See estimated LMP, ovulation date, and conception range in one view.
Ultrasound Support
Enter weeks + days from a dating scan for the most accurate result possible.