here is a summary of the april 2016 postage rate updates first class mail letters 1 oz rates will decrease from $ 0 49 to $ 0 47 when purchased at the post office each additional ounce will cost $ 0 21 the discounted metered mail category for first class mail letters 1 oz which includes online postage providers and postage meters will decrease from $ 0 485 to $ 0 465 