Lines company Nelson Electricity has admitted it is making too much money and will reduce its income next year as compensation.
In a settlement with the Commerce Commission, the company admitted earning just under $91,793 more than it should have for the year to March 2017.
That amounted to $5 to $6 a year for an average residential customer.
The company said this was done in error and it would reduce its total earnings by at least $105,075 for the next financial year.
Nelson Electricity said it was not clear how much effect this would have on bills because transmission, local government rates and other costs had to be factored in.
It has pledged no one will be worse off because of the error.