How often did the pony express riders change horses?

Pony Express riders changed horses approximately every 10 to 15 miles. This allowed them to maintain a rapid pace while covering the roughly 1,900 miles between St. Joseph, Missouri, and Sacramento, California. Each rider would typically travel a leg of about 75 miles before passing the mail to another rider at designated relay stations. The entire route was designed to ensure the mail could be delivered in about 10 days.