Hospitals already have to make prices for procedures available on request, but a new rule requiring them to post the information online goes into effect on Jan. 1, 2019.

The move toward price transparency sounds like a step in the right direction — part of government efforts to encourage patients to become better educated decision makers in their own care and shop around for the best value for, say, a colonoscopy.

But some health care advocates warn the new requirement is not as straightforward as it appears and may be confusing to consumers.

“This is the list price. When you go to buy a car, you have a manufacturer’s suggested retail price — this is basically what it is,” said NBC News medical contributor Dr. Natalie Azar on TODAY Friday.

“The concern is that there’s a big difference between what the list price is and what the actual transaction price is — the cost the patient is responsible for.”

Almost no one pays the charges indicated on the price list, said Dr. Ira Nash, senior vice president and executive director of Northwell Health Physician Partners in New York. The real prices are the result of negotiations with insurance companies and those are not published, he added.

That list price may also not be that meaningful to patients because they still have to go back to their insurance company and find out what their bottom line — the patient responsibility — is going to be, Azar noted. That can depend on each patient’s co-pays, co-insurance and deductibles.

So the new policy is a nice step forward, but “falls far short of being effective or useful for most people,” said Jeanne Pinder, founder and CEO of ClearHealthCosts.

“Publicizing the list price has the paradoxical effect of causing people to believe that these prices — inflated and fanciful — actually represent what they cost,” she said.

There’s a legitimate concern the new policy is not going to benefit consumers and could confuse patients more than help them, added Benendic Ippolito, research fellow in economic policy at the American Enterprise Institute.

The prices also won’t help people in a crisis who can’t exactly price compare what the hospitals in their area charge as they’re rushed to the ER, Azar pointed out.

She recommended patients who aren’t facing an emergency become informed about the prices, but also consider each hospital’s safety record, quality of care and aspects such as location.

“If you have time to plan for something, I think you can make smart decisions,” Azar said.

NBC News medical researcher Judy Silverman contributed to this report.