The St. Petersburg-based utility filed its request Friday with the Florida Public Service Commission.
The proposal would cut the overall bill for 1,000 kilowatt hours per month, which is about average, by $7.44 down to $115.75.
The reduction would include a $129 million refund to customers the commission already has approved for 2013 as part of a prior rate settlement with the utility.
It purchases power from other sources to cover shortfalls including those resulting from the extended shutdown of a nuclear reactor in Crystal River.
Progress, a subsidiary of North Carolina-based Duke Energy, serves 1.6 million homes, businesses and other customers in central and north Florida.