http://www.usps.com/prices/
On May 12 we will adjust prices for mailing services — First-Class Mail, Standard Mail, Periodicals, Package Services, and Special Services. The average increase by class of mail is at or below the rate of inflation as measured by the Consumer Price Index.
A First-Class Mail stamp will be 42¢. Customers can continue to use the Forever Stamps that they purchased prior to May 12 at 41¢, even after the price change.