SSE, which has around 10 million customer accounts, blamed the increased cost of buying and delivering wholesale energy as well as Government levies collected through bills.
It said the latest increase, which is three times the rate of inflation, would come into effect from November 15.
The company, which trades as Southern Electric, Swalec and Scottish Hydro, said the hike equated to an average £2 a week for a typical dual fuel customer.
After SSE announces gas and electricity tariffs will prices will rise next month, other big energy firms refuse to rule out own price hikes.
Some tips on how to save money on your energy bills.