Under current rules, suppliers can put up prices without notifying customers for up to 65 days afterwards.
The rules will come into effect at the start of 2011, providing suppliers do not object. Energy secretary Chris Huhne has already warned that the government may take legal action against energy firms if they block reforms.
“This is a welcome step forward in getting energy companies to play fair with their customers by giving advance notice of price increases,” said Huhne.
He added: “It’s important people know about price hikes before they are charged, so they can budget.”
The regulator said that new rules would give householders more chance to switch supplier or reduce their energy use to help counter the effect of increased prices.
“This information makes it easier to shop around for a better energy deal and to evaluate the benefits energy efficiency measures can deliver,” said Andrew Wright, Ofgem’s senior partner for markets.
Wholesale gas prices have soared in 2010, pushing up wholesale power prices and raising the possibility of further retail price hikes.