If you've ever opened an envelope from Medicare or your insurance plan and seen a document labeled "This Is Not a Bill," and then panicked anyway, you're not alone. The Explanation of Benefits, or EOB, is one of the most misunderstood pieces of mail seniors receive. Here's what it actually means, and why it's worth a quick read each time one arrives.

An EOB is a summary of a medical claim that's already been processed. It shows what your doctor or provider billed, what Medicare or your plan paid, and what, if anything, you may owe. It is not a bill. Think of it as a receipt confirming that a claim was reviewed, not a request for payment.

Most EOBs follow a similar layout, even if the wording varies by plan:

• ​Provider & Service Date - who you saw and when.
• ​Amount Billed - what the provider originally charged.
• ​Plan Discount / Allowed Amount - the negotiated rate your plan actually recognizes, often lower than the billed amount.
• ​Your Responsibility - any copay, coinsurance, or deductible amount you may owe the provider directly.

​If a separate bill arrives from your provider, that's the one to pay, not the EOB itself.

• Catch billing errors early. Wrong dates, duplicate charges, or services you never received can show up here before they become bigger problems.
• ​Track your deductible and out-of-pocket spending. EOBs are a running record of where you stand for the year.
• ​Spot potential fraud. If you see a service listed that you don't recognize, it's worth a call to your plan or provider.

Call the customer service number on the EOB or your plan card. Have the claim number correct it and reissue a corrected EOB.

• Keep EOBs in a folder or binder by year, they're handy for tax time and for tracking healthcare spending.
• ​Compare your EOB to your provider's bill before paying anything.
• ​If the wording feels confusing, most plans have a member services line specifically for questions like this.