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 will leave many patients overwhelmed. Procedures are described in medical jargon and abbreviations. "The information is not user-friendly," said AARP's David Certner.

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, has called the postings a first step to increase transparency about health care costs.

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 insurers, states and other groups also have online cost estimators. Accuracy varies. 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 whether outpatient care is an option; it's normally cheaper.

• Check with your insurer to see whether you need preauthorization and confirm the hospitals and doctors are in network.

• 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 clearhealthcosts.com works with newspapers and TV newsrooms in a dozen metropolitan areas and is adding more, said founder Jeanne Pinder. It builds databases of hospital and outpatient clinic prices. 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.

"It's very complicated and difficult for people to get a complete picture of what their costs will be" in advance, said Dena Mendelsohn, health care policy expert at Consumer Reports. 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 are charged far more than was estimated, appeal to the hospital and insurer. If you don't get results, contact your state's insurance regulator.

Linda A. Johnson writes for the Associated Press.