The cost of a one-ounce First-Class Mail® stamp is $0.73 at the Post Office, or $0.69 if you buy and print stamps online using Stamps.com. Get Postage Stamp Discounts with Stamps.com When you purchase postage stamps online using a PC Postage vendor such as Stamps.com, you are eligible to receive postage rate discounts.

A First-Class Mail ® Forever stamp costs $0.73 and goes in the upper right corner of the envelope. (You can also use any combination of stamps that adds up to $0.73.) If your letter is heavier or bigger, or if you want to add insurance or extra services like Certified Mail ® service, you'll pay more. A standard postcard stamp costs $0.56.