Sonic: 1/2 off Cheeseburgers- 8/13 Only 08/10/2015 By MFA 1 Comment This post may contain affiliate links, please see my disclosure policy. Sonic is offering half off cheeseburgers on August 13th. No coupon needed and the offer is valid all day long. If you stop by from 2-4pm, you can also get 1/2 price drinks and slushies! Click here for more information.