More than one million Australian households have been warned they could be paying up to $150 more a year on their electricity bills by staying on outdated energy plans.

A new rule will require power companies to alert customers who have remained on the same plan for four years or longer.

The warning is designed to encourage households to compare offers and switch to cheaper plans if better deals are available.

Consumer groups say many loyal customers continue to pay significantly more than new customers for the same service.

Energy experts are urging Australians to review their electricity plans regularly to avoid unnecessary costs.

The changes come as families continue to face cost-of-living pressures and rising household expenses.