Bill Audit Guide

Find the errors in any bill

By Dan Donovan, @askdandonovan

Most people argue about the total. You can't win that, because the total is just a number someone typed. This is the other way round: get the detail, then check it against the rules the bill is supposed to follow.

5 Steps
3 Copy-paste blocks
6 Error types
$0 Extra cost

The idea in one line

Almost everything that sends you a bill has to follow a published set of rules, and almost nobody ever checks the bill against them.

Those rules are written down. Some of them are law, some are the contract you signed, some are a regulator's code of practice. Either way, they exist in a document somebody can read, and until recently reading them was the expensive part.

What you need: the bill, and a Claude account at claude.ai. The free plan handles this, since it's one document and one conversation. If your bill runs to dozens of pages you may hit a usage limit and need to wait or split it up.
What you'll have after this
The request message
Gets you the itemised bill instead of the summary
The audit prompt
Checks every line against six error types
Your rulebook
Which one applies, by bill type and country
The verification step
How to confirm a finding before you use it
The query letter
Names the rule, doesn't ask for a favour
The honest limits
What this won't do, so you don't waste a week
Do this in the next 10 minutes

Ask for the itemised bill

You can't audit a summary. Send this now, before you read the rest, because it's the one step with a waiting period attached.

Send to the billing department 
Hi, could you please send me a fully itemized statement for account [NUMBER], showing every individual charge, its code or reference, and the date it was applied.

Thank you.

Where this came from

Matt Rosenberg had a heart attack in June 2025. Four hours of emergency care in a United States hospital, and the bill came to $195,628.

He gave the itemised bill to Claude and asked it to check the charges against Medicare's billing rules. One stent procedure had been split apart and charged as separate line items for the catheters, the wires and the supplies, when all of that is meant to be billed together under a single code. There was a procedure on the bill he never had. And there was a ventilation charge sitting next to a code it isn't allowed to sit next to.

Claude wrote a six page letter walking through each rule the bill had broken. He settled for about $32,500, roughly $163,000 off. He wrote the whole thing up himself in Business Insider in February 2026.

Two honest notes. That's a United States hospital bill, and US medical billing is unusually broken, so the numbers there are extreme in a way they won't be on your phone bill. And it's one case, not a study. Nobody can tell you the odds your bill is wrong. What you can say is that checking costs you an afternoon at most.
1

Get the itemised version

This is the step people skip, and it's the one that makes everything else possible.

What you normally get is a summary. One line, one total, maybe a category. There's nothing in a summary to check, because a summary is a conclusion. What you want lists every charge separately, usually with a code or reference next to each one.

Those codes matter more than the descriptions. Descriptions are written for you. Codes are written for the system, and the system has rules about which codes are allowed to appear together.

Two small things. Ask in writing if you can, so you have a record of the date you asked. And you don't need to explain why you want it.
2

Find the rulebook that applies to you

Every bill sits on top of some published set of rules. You're looking for whichever one covers yours. You don't have to read it. You just have to know which one it is and get it in front of Claude, as a file, a link, or a name.

Rules are local. This is the part people get wrong. Here are real examples of the kind of thing you're looking for:

United Kingdom, energy Ofgem bans suppliers from back-billing domestic customers for energy used more than 12 months ago where the supplier was at fault. There are exceptions, mainly where a customer blocked meter access or tampered with the meter. Ofgem
Australia, energy Under the National Energy Retail Rules, retailers generally can't recover undercharged amounts from more than 9 months before they told you, where the error was theirs. Victoria is tighter at 4 months since January 2021. Essential Services Commission
United States, energy No single national rule. Back-billing limits are set state by state, so the document you want is your state public utility commission's billing rules.
United States, medical Medicare publishes which procedure codes are allowed to be billed alongside each other, through the National Correct Coding Initiative. CMS updates those tables quarterly. CMS
Anything you signed For trades, contractors, professional services and insurance, the rulebook is the quote, the contract, or the policy document. It's the one people forget they already have.
Careful with the word Medicare. In the United States it's federal health insurance with its own coding rules. In Australia it's the universal public system, and it works nothing like the American one. If you're outside the US, the medical example above isn't your rulebook.
3

Run the audit

Attach the itemised bill and paste this in. Fill in the bracketed parts first, especially the country. If you skip that, Claude will guess, and it usually guesses American.

The audit prompt 
I'm going to give you an itemized bill and I want you to audit it properly.

Here's my situation:
- Bill type: [medical / energy / phone / insurance claim / contractor / other]
- Who issued it: [company or organisation]
- Country and region: [be specific, the rules are local]
- What I was told it would cost: [quote, estimate, policy limit, or "nothing"]
- The rulebook, if I have it: [attach, link, or name it]

Do this in order:

1. Read every line item back to me in plain language. No jargon. If a line is
   vague or you can't tell what it's for, say so and flag it.

2. Tell me which rules apply to this bill in this country and region. Name the
   specific documents or standards. If you're not sure a rule exists or applies,
   write "unverified" next to it. Do not invent regulations.

3. Check the bill against those rules. Look for:
   - the same thing charged twice under different names
   - one item split into several charges when it should be billed as one
   - charges for something that never happened or wasn't delivered
   - two charges that aren't allowed to appear together
   - charges outside what I was quoted, or outside what the policy covers
   - anything billed at the wrong rate, date, or quantity

4. For every problem, give me: the line, the amount, the rule you think it
   breaks, and how confident you are. Separate the things you're certain about
   from the things that just look odd.

5. Total up the amount actually in question. Be conservative. I would rather
   query five things that are real than fifty that aren't.

Then stop. Don't write me a letter yet.
That last line matters. Get the findings first and look at them yourself before anything gets written on your behalf.
4

Check every finding at the source

Don't skip this one. AI can state a rule that sounds completely real and doesn't exist. If you send someone a letter citing a regulation that was never written, you've handed them the easiest possible way to dismiss you, and you've damaged your credibility for the rest of the dispute.

For every finding you plan to actually use:

  • Ask Claude for the exact source. Document name, section, and a link.
  • Open the link yourself and read the section.
  • If you can't find it, or the link doesn't resolve, drop that point entirely.

You'll usually lose a couple of findings this way. The ones that survive are worth far more, because every one of them holds up.

5

Send a letter that names the rule

Once you have a shortlist you've checked yourself:

The letter prompt 
Write a short, calm letter querying these charges.

Rules:
- One paragraph per issue. The line item, the amount, and the specific rule it
  breaks, named exactly.
- Only use the findings I've confirmed. Nothing else.
- Ask for a corrected statement. Don't propose a settlement figure and don't
  ask for a discount.
- No threats, no legal language, no emotion. Plain and factual.
- End by asking them to confirm receipt and put the account on hold while it's
  reviewed.

Notice what that letter isn't doing. It isn't asking for a favour, and it isn't arguing about the total. It points at their own rules and asks them to apply them, which is a much harder thing to say no to, because the answer isn't up to the person reading it.

Send it in writing. Keep a copy of everything.

What this won't do

The short version