Marie Cox is paying extra in her Duke Energy Florida bill this month.

It's not of her choosing. It's not because she's using more electricity than she typically does this time of year.

She's paying more because Duke is reorganizing the way it reads meters. As a result, Duke is temporarily extending its billing cycle, typically a month, by as many as 12 extra days. Here's how it affects customers:

The additional days mean that about 267,000 customers face bigger bills, and some, like Cox, will also pay higher rates.

That's because Duke charges customers $11.34 for every 100 kilowatt hours of usage up to 1,000 kilowatt hours. But above that, it charges $13.70 for every 100 kilowatt hours.

For Cox of St. Petersburg, all the electricity use during those additional days was charged at the higher rate. She said it was outrageous given that it is Duke that is making changes to its system at customers' expense.

Multiply the difference between the standard rate and the higher fee, Cox said, and Duke could collect hundreds of thousands of dollars — for nothing.

"That's a chunk of change that Duke really didn't earn," said Cox, a retired mathematician who worked for the U.S. Department of Defense. "It's smoke and mirrors in the accounting room."

J.R. Kelly, the state public counsel who represents consumers before the Public Service Commission, said Duke is allowed under state regulations to charge customers the extra money. But Kelly agreed with Cox that Duke is profiting from the change in its meter reading system.

"The bottom line is they're charging consumers for something that is not the consumers' fault," Kelly said.

Can't afford it?

No worries. Duke will offer you a payment plan.

The utility acknowledges that some customers will pay a higher rate for the extended billing cycle but offers no reduction in the charge.

Nicole LeBeau, a Duke spokeswoman, said the utility is simply following state rules. She said customers should contact customer service for assistance with their bills if they have trouble making the payments that the change created.

"We will work with every single impacted customer who may need to discuss payment arrangements," LeBeau said.

Duke informed customers of the change in letters and phone calls over the past few weeks. "We apologize for any inconvenience this may cause and appreciate your understanding as we strive to make our service to you more efficient," Duke said in its letter to customers.

The utility also posted questions and answers on its website.

Duke said it is eliminating duplicate routes traveled by meter readers. "The result will mean fewer miles driven by our employees, faster response time to reconnect customers and a more efficient business process," LeBeau said.

The change in the meter routes will affect 650,000 customers and conclude next month. More than half of those customers will receive shorter or normal bills, while 41 percent, or roughly 267,000 customers, will receive the extended bill.

Duke informed state regulators of its plans, and the Public Service Commission said the process the utility is using is in line with its policies.

Cox said the commission's acknowledgement that Duke has the right to charge the fees provides little comfort.

"So what?" Cox said about the commissioners. "They're not on our side."

Contact Ivan Penn at ipenn@tampabay.com or (727) 892-2332. Follow @Consumers_Edge.