What's the difference?
The Due Date Calculator uses standard formulas to estimate the date your baby might be due.
The most common way to calculate your due date is using the date of your last period. Using this method, the due date calculator adds 280 days (40 weeks) from the first day of your last period.
Conception date is used less frequently as many women are not sure of this exact date. Using this method, the calculator will add 266 days (38 weeks) to estimate your due date.