Final answer:
Nagele's rule suggests adding 3 months to the first day of the last menstrual period and adding 7 days to estimate the delivery day.
Step-by-step explanation:
To calculate an estimated delivery day using Nagele's rule, you need to add 3 months to the first day of the last menstrual period and add 7 days. This rule assumes that conception occurred on day 14 of the menstrual cycle, which is usually a good approximation. For example, if the first day of the last menstrual period was August 1st, the estimated delivery day would be May 8th (August 1st + 3 months + 7 days).