About the Pregnancy Conception Calculator
Estimate when conception most likely happened. Enter your due date or last period date to see the estimated conception date and the fertile window around it.
How to use it
- Choose due date or last period.
- Enter the date (and cycle length for last period).
- See the likely conception date and range.
Formula & method
Conception ≈ Due date − 266 days
Fertile window ≈ conception − 5 days to + 1 dayFrequently asked questions
How accurate is a conception date estimate?
Only roughly. Ovulation timing varies and sperm can survive up to five days, so conception could have happened several days either side of the estimate.
Results are estimates for general information only and are not financial, tax, legal or medical advice. Please confirm important decisions with a qualified professional.