Sonic – Buy 1 Get 1 Free Burger Coupon This post may contain affiliate links and I may be compensated for this post. Please read our disclosure policy here. February 22, 2011 Sharing is caring!0sharesShareTweetPin Sonic has a printable coupon for buy 1 1/4 lb Sonic Burger, get another one FREE. This coupon is valid at participating Sonic locations & is valid thru Monday, February 28th. Thanks Coupon Cookin!