What's an EOB? A Plain-English Guide for Real People

You've seen it. It arrives in an envelope, usually stamped 'THIS IS NOT A BILL' in a font designed to be ignored. The Explanation of Benefits — EOB for short — is one of the most important documents in your healthcare life, and almost nobody reads it.

That's a costly mistake. Medical billing errors are more common than you'd think: one study found errors in up to 80% of medical bills. An EOB is how you catch them before they cost you.

What an EOB Actually Is

An EOB is a statement your insurance company sends after you receive medical care. It shows what your provider charged, what your insurance negotiated down to (the 'allowed amount'), what your insurance paid, and what you owe. It's a record of the transaction — not the actual bill from your provider.

Think of it as a receipt showing the insurance company's math. If the math is wrong, you need to catch it before paying your provider's bill.

The Four Numbers That Matter

Every EOB looks slightly different, but they all contain the same core information.

• ✓Billed amount: What your provider charged before any negotiation. This number is almost always inflated and rarely what you'll pay.
• ✓Allowed amount (or 'negotiated rate'): What your insurer agreed to pay for this service. This is the real price — often 40–60% lower than the billed amount.
• ✓Plan paid: What your insurance company paid directly to your provider.
• ✓Your responsibility: What you actually owe. This is the only number you should be writing a check for.

Common Billing Errors to Catch

Duplicate charges are the most common error — the same service billed twice. Check that each procedure code (the 5-digit CPT codes) appears only once per visit. Upcoding happens when a provider bills for a more expensive service than what was performed. If your 10-minute follow-up was billed as a 45-minute complex visit, that's upcoding.

Wrong patient information — your name, date of birth, or insurance ID entered incorrectly — can cause legitimate claims to get denied. And unbundling is when services that should be billed together are split into separate charges to maximize reimbursement.

What to Do If Something Looks Wrong

First: don't pay anything until you reconcile your EOB with your provider's bill. They should match. If they don't, call your provider's billing department first. Most errors are administrative mistakes, not fraud, and billing departments are used to fixing them.

If you can't resolve it with your provider, call your insurance company. Every EOB has an appeal deadline — usually 180 days from the date of service. Don't let that window close.

If you believe your insurance company denied a valid claim, you have the right to appeal. Start with the internal appeal process, and if that fails, most states have an independent external review process that's free to use.

One Habit That Saves Money

Set a calendar reminder to check your online insurance portal 2–3 weeks after any medical visit. EOBs often arrive there before they hit your mailbox. Catching an error at that stage — before you've paid your provider — is much easier than disputing a charge after the fact.