Conception date calculator
Estimate the likely conception date from your last period, your due date or an ultrasound.
How the conception date is calculated
Conception is estimated 14 days after the first day of the last period in a 28-day cycle. When you enter the due date, the tool goes back 280 days to find the equivalent last period and from there estimates conception.
In ultrasound mode, the scan date and gestational age define the start of the pregnancy, which is usually more accurate when the LMP is uncertain or the cycle is irregular.
Calculation based on Naegele's rule and the standard luteal phase length, as described in obstetric textbooks.
Frequently asked questions
Important notice
This calculator is an educational tool and does not replace a medical consultation. Results are estimates based on published models and may not apply to your case. Never make decisions about your health or your pregnancy without advice from your doctor.
Reviewed by: Dr. Peterson Fernandes — CRM-MG 42452 · RQE 37814
Last reviewed: 11/3/2026