How is the new expiration date on a passport renewal calculated?

Question: Does the new expiry date for a renewed passport come 10 years from the applicaiton date or 10 years from the date the old passport will expire?

Source: http://www.us-passport-service-guide.com/how-is-the-new-expiration-date-on-a-passport-renewal-calculated.html

united states passports online passports us passport application