Pregnancy due date calculators provide an estimated date of delivery based on a woman's last menstrual period or conception date. While actual delivery dates often occur before or after this estimate, the calculator allows women to prepare and track their pregnancy progress. Ultrasounds during each trimester also help doctors monitor the baby's development. Online calculators offer additional features like weekly updates and diet/exercise tips tailored for each trimester. However, no calculator can predict the exact delivery date, so women should not panic if delivery occurs before or after their estimated due date.