DEAR SAVVY SENIOR: I need some help understanding my medical bills from my knee replacement surgery earlier this year. My wife and I live on a pretty tight budget so I like to keep track of our costs as closely as possible. But the bills I’ve received are vague and confusing, and we think we’re being overcharged. What can you tell us? — Trying To Recover

DEAR TRYING: Errors and overcharging have become so commonplace on medical bills today that double-checking them is a very smart move that may save you some money. Here are some tips and tools that can help:

According to the Medical Billing Advocates of America, nine out of 10 hospital bills have errors on them, most of which are in the hospital’s favor. Bills from doctor’s offices and labs have mistakes too, but they tend to be fewer and further apart.

To help you get a handle on your medical bills and check for costly errors, the first thing you need to do is request an itemized statement from the hospital or health care providers detailing the charges of the procedures, supplies, tests and services they provided you. They are legally required to provide you with this information.

If the statement contains confusing billing codes or abbreviations that you don’t understand, call the billing office for an explanation. You can also look up most medical billing codes online by going to any online search engine and typing in “CPT” followed by the code number.

Once you receive and decode the statement, review it carefully and keep your eyes peeled for these mistakes:

• Double billing: Being charged twice for the same services, drugs or supplies.

• Typos: Incorrect billing codes or dollar amounts.

• Canceled work: Charging for a test your doctor ordered, then canceled.

• Phantom services: Being charged for services, tests or treatments that were never received.

• Up-coding: Inflated charges for medications and supplies.

• Incorrect length of stay: Most hospitals will charge for the admission day, but not for day of discharge. Be sure you’re not paying for both.

• Incorrect room charges: Being charged for a private room, even if you stayed in a semi-private room.

• Inflated operating room fees: Being billed for more time than was actually used. Compare the charge with your anesthesiologist’s records.

To make sure the charges on your bill are reasonably priced, use the Healthcare Blue Book at healthcarebluebook.com. This is a free resource that lets you look up the going rate of health care costs in your area.

If you find errors or have questions about charges, contact your provider’s billing office and your insurer. If they don’t help you and the discrepancies are significant, you should consider getting help from a trained professional who specializes in analyzing medical bills and negotiates with health care providers, insurers and even collection agencies.

Most medical bill reviewing professionals charge an hourly fee — somewhere between $50 and $200 per hour — for their services, or they may work on a contingency basis, earning a commission of 25 percent to 35 percent of the amount they save you.

To find help, check out resources like Medical Billing Advocates of America (billadvocates.com), MedReview Solutions (medreviewsolutions.com), Hospital Bill Review (hospitalbillreview.com) and Medical Cost Advocate (medicalcostadvocate.com). You can find others by doing an Internet search under “hospital bill review.”

If you’re a Medicare beneficiary, another resource that may help is your State Health Insurance Assistance Program, or SHIP.

It provides free personalized counseling and may be able to help you get a handle on your medical bills and Medicare coverage. To find a local SHIP counselor visit shiptalk.org, or call (800) 677-1116.

Send your senior questions to: Savvy Senior, P.O. Box 5443, Norman, OK 73070, or visit SavvySenior.org. Jim Miller is a contributor to the NBC “Today” show and author of “The Savvy Senior” book.