Estimate by Due Date

Estimate By Due Date
Do you know the due date that the doctor gave you for the individual in question?  If yes, then use this calculator to estimate the conception date by the given due date. 

* Please note: This is only an estimate based on averages.

Using Naegele's Rule.

  •  Assumes 266 days from conception to birth.
  •  Assumes the doctor use this rule to estimate due date.
  •  
Individual's Due Date:              
                                         (MM/DD/YYYY format)


 

Estimated Conception Date:

 

What is the "normal gestational term" for humans?

Naegele’s Rule: The standard definition for gestational term is 266 days from conception to the date of the baby’s birth. This is also defined as 280 days, or 40 weeks, from the first day of the mother’s last menstrual period, a definition which assumes that the mother ovulates on day 14 of a 28 day menstrual cycle. The formula used to calculate due date is:

(LMP + 7 days) – 3 months = Due Date

This definition is based on observations, first reported by Franz Naegele in 1812, who believed that pregnancy lasted ten lunar months from the last menstrual period. It was not based on empirical data.