What is the estimated date of birth for a client whose last menstrual period was July 13?

The estimated date of birth calculation is based on Naegele’s Rule, which is a formula used to determine a due date based on the first day of a woman's last menstrual period (LMP). The formula involves adding one year, subtracting three months, and adding seven days to the date of the LMP.

For a client whose last menstrual period was July 13, the calculation would proceed as follows:

1. Start with the last menstrual period: July 13.

2. Add one year: July 13 of the following year.

3. Subtract three months: April 13 of the following year.

4. Add seven days: April 20 of the following year.

Thus, using Naegele's Rule accurately determines that the estimated date of birth is April 20. This method is widely accepted in obstetrics for calculating estimated due dates and is why April 20 is considered the correct answer.