Conception Timing Calculator

Method, assumptions & sources

Who this is for

Adults seeking a pregnancy-dating estimate from a known date or a clinician-reported gestational age.

How it works

Determine an estimated due date from the selected dating basis, then subtract 266 days. Display five days before through one day after the model fertilization date as a survival-time interval, not a confidence interval.

Keep in mind

• Dates cannot identify a particular intercourse event, establish paternity, or prove conception occurred.
• This does not predict the delivery day or replace the due date established by your maternity team.
• A reported ultrasound age is converted into dates; scan images and fetal growth are not assessed.

Sources

• ACOG: methods for estimating the due date (opens in a new tab)
• ACOG: fertility awareness methods (opens in a new tab)