TRENTON, N.J. >> Want to know how much your hospital is going to charge for that knee surgery?

U.S. hospitals are now required to post list prices for medical services online, under federal rules meant to help patients find affordable care and avoid hefty surprise bills. The spreadsheets, often thousands of lines long, will leave many patients overwhelmed. Procedures are described in medical jargon and abbreviations. That’s if you can find the lists.

“The information is not user-friendly,” says AARP’s David Certner.

WHAT IS POSTED ONLINE

Most hospitals list standard charges which are far above the prices negotiated by insurance companies. But the posted charges for a surgery, for example, don’t include separate things like room rates for overnight stays. They don’t include fees for every doctor involved in a patient’s treatment. And doctors outside a patient’s insurance network could send big bills separately.

Certner said many people will find it hard to compare hospitals because they use different formats to list charges.

Seema Verma, administrator of the U.S. Centers for Medicare and Medicaid Services, recently called the postings a first step to increase transparency about health care costs. The rule went into effect Jan. 1.

The lists don’t show the out-of-pocket costs most patients face, which vary depending on their insurance. Verma said some hospitals already have online tools letting patients enter their insurance information to get estimated charges.

Some major insurers, states and other groups also have online cost estimators. Accuracy varies; Consumer Reports reviewed some of the sites. Medicare patients can look up estimated costs for outpatient procedures.

WHAT TO LOOK FOR

If you need surgery, tests or other hospital services, experts advise price shopping. Call your insurer and check charges at multiple hospitals.

— Get the exact description of the test or procedure from your doctor and the billing codes, usually a DRG code for a bundle of related services or multiple CPT codes for treatment components. Ask if care can be provided as an outpatient, which is normally cheaper.

— Check with your insurer to see if you need preauthorization and confirm the hospitals and doctors are in network. That can change with insurers’ contracts each January, and online directories can be out of date.

— Ask the hospital what it will charge for the procedure, each doctor or other provider’s services, medications, supplies, daily room rates and the facilities fee, which can be charged even for services off the hospital campus.

— Ask your insurer what it will reimburse for all those charges and what your estimated costs will be.

The website www.clearhealthcosts.com works with newspapers and TV newsrooms in a dozen metropolitan areas and is adding more, says founder Jeanne Pinder. They build databases of hospital and outpatient clinic prices by calling and asking what they charge patients paying cash, a helpful benchmark. Pinder said paying cash can sometimes be cheaper than the out-of-pocket costs with insurance. The site lists what Medicare reimburses for procedures by zip code, another good measuring stick. It also lets patients post what they paid at specific hospitals.

WHEN YOU GET THE BILL

“It’s very complicated and difficult for people to get a complete picture of what their costs will be” in advance, says Consumer Reports health care policy expert Dena Mendelsohn. That’s partly because complications can occur and services can vary from estimates.

Her advice:

— Keep records of all cost information provided by your insurer and hospital staff. If possible, get it in writing, in case of problems.

— Get an itemized bill. Before paying, check your insurer’s explanation of benefits and confirm you received every service listed.

— If you’re charged far more than was estimated, appeal to the hospital and insurer to adjust your bill. If you don’t get results, contact your state’s insurance regulator.