A big credit reporting bureau is taking another step to allow people with scant or marred credit histories to improve their odds of getting loans and credit cards.

Experian, one of the three major credit bureaus, said this week that in January it will start Experian Boost, a free, optional service that lets consumers supplement their credit report with information about their history of paying utility, cable and cellphone bills.

The extra information may help improve consumer credit scores, the three-digit numbers that lenders use to decide whether borrowers are likely to repay loans.

Traditional credit reports include your history of paying credit card bills and loans but typically don’t include data on these kinds of bills unless the accounts are delinquent.

The new service aims to reward consumers who pay those bills on time, said Gregory Wright, chief product officer with Experian’s consumer bureau.

The service could potentially benefit millions of consumers who have “thin” credit files — meaning they have few credit card or loan accounts on their reports — or are considered “subprime” borrowers, with scores too low to meet many lenders’ requirements.

There’s a catch or two: You must have an online bank account, and give Experian an electronic peek at it. Experian will work with Finicity, a financial technology firm, to scan bank statements and identify eligible payments. The system uses read-only access, so it cannot alter a user’s data. “Data security is our No. 1 priority,” Wright said.

Consumers must give Experian explicit permission to identify eligible bills and add them to their credit report, and can revoke it at any time. Only positive payment history is included, he said.

Experian found that adding the additional bill-payment information helps increase a user’s credit score about two-thirds of the time, Wright said; in about a third of cases, it has no effect. (Rarely, the extra information may lower a score slightly; in that case, a consumer could just cancel access to the service, he said.)

Experian Boost will be available directly to consumers before they apply for credit. They can sign up on Experian’s website or, eventually, on its mobile app.

Lenders will be notified when the credit report they are provided is based on extra consumer information, he said.

One drawback is borrowers generally don’t know in advance whether a specific lender uses Experian to evaluate scores; lenders may also check an applicant’s credit using Experian’s competitors, Equifax and TransUnion. If a lender doesn’t use Experian, it can’t obtain the consumer’s Boost score.

Consumer advocates are cautiously optimistic about the potential of using consumer-selected information to broaden the availability of credit.