Final answer:
The formula for calculating a woman's estimated due date is based on the first day of her last menstrual period, adding 280 days (or 40 weeks) to it. However, the actual date of delivery may vary.
Step-by-step explanation:
The formula used to calculate a woman's estimated due date (EDC) is based on the first day of her last menstrual period. The EDC is calculated by adding 280 days (or 40 weeks) to the first day of the last menstrual period.
For example, if a woman's last menstrual period started on January 1st, her estimated due date would be 280 days later, which falls around October 8th.
It's important to note that the EDC is an estimate and may not be the exact date of delivery, as pregnancy lengths can vary.