How-to · Re-checking your tax return with AI

A second read by AI turned an accountant's tax return from owing $30,000 to getting $30,000 back

Give Claude the tax return your accountant prepared, along with the supporting documents, and ask for a second review. The AI can find missed deductions and calculation errors. Every case collected here involves a US tax return, and in each one the accountant accepted the findings and fixed the return.

Oct 23, 2026·3 cases

A comment by Hacker News user weird-eye-issue, with a yellow highlight on the line saying this year's return went from owing $30,000 to getting $30,000 back — A comment from weird-eye-issue, a Hacker News user who lives outside the US. After the accountant fixed the problems Claude Code found, this year's return went "from owing 30k to getting 30k back." Working Reference added the yellow highlight. Source: Hacker News

weird-eye-issue — What the accountant missed (reply, about $100,000 in total), 2026-10-15

weird-eye-issue — Finding the accountant's mistakes with Claude Code and amending, 2026-10-15

Alex Willen — Doing My Taxes With Claude, 2026-03-05

In October, around the US extension deadline, similar posts kept showing up in Hacker News comment threads. People had AI reread a tax return their accountant prepared, and it turned up things the accountant missed. One user who lives outside the US wrote that after the accountant fixed the problems Claude Code found, the return just filed for this year went "from owing 30k to getting 30k back."

Here is how it works. You give the AI the return your accountant prepared, along with every income document and record behind it, such as W-2s, K-1s, 1099s, and your books. Then you have it check whether the numbers on the return match the documents and whether any deductions are missing. Most people used Claude's Projects feature or Claude Code.

Reference 01weird-eye-issue, a Hacker News user living outside the US

Claude Code found two deductions the accountant missed. With past years amended too, about $100,000 is coming back

weird-eye-issue used Claude Code to review the return their accountant had prepared. Claude Code found two missing items: a deduction available to people living outside the US, and a deduction for a loss from the previous year on a rental property that had already been sold. Asked how they did it, weird-eye-issue replied, "It wasn't a trick, it was just pretty standard stuff in my situation that they completely forgot to take advantage of."

The accountant revised this year's return and filed amended returns for the past several years. weird-eye-issue wrote that the $30,000 refund on this year's return plus the refunds from the amended returns come to about $100,000.

Reference 02Alex Willen, who acquires and runs brands · The Automated Operator newsletter

The AI said everything looked fine. Told to go through every document, it came back 10 minutes later with the goodwill deduction the accountant missed

Willen put the 2024 return and the supporting documents sent to the accountant into one folder and asked Claude Code to review them. Claude was already handling Willen's bookkeeping, so it knew the business. Asked to find errors and missed deductions based on the documents in the folder and what it knew about the business, it answered "suspiciously quickly" and said everything was fine. When Willen pushed back, Claude admitted it had not checked the original documents.

So Willen ran it again in plan mode with the prompt below. Claude worked for 10 minutes, then reported that the accountant had missed a deduction. Willen explained that when you acquire a brand, the part of the purchase price that counts as goodwill can be amortized over 15 years, deducting one-fifteenth each year. The accountant had not claimed this goodwill amortization.

The accountant's first reply was "Yes. As long as you purchased the goodwill, you can depreciate them. We will start depreciating the goodwill from 2025." Under that plan, the 2024 return already filed would still be missing the goodwill deduction. So Willen asked the accountant either to amend the 2024 return for free or to cover the loss from the mistake, in the amount Claude had estimated. Only then did the accountant apologize and agree to file an amended return.

The prompt Alex Willen sent the second time

go into plan mode and come up with a comprehensive plan to review every single document, check every number in the return and then think through all potential deductions given the information available to it

Plan mode is a Claude Code feature. Willen wrote that once the work is done, it costs nothing to ask whether anything was skipped and whether every file was actually read.

Willen asks whether the accountant's mistake is excusable, and Claude says no and gives four reasons — Willen asked, "Is this excusable?" and Claude answered, "No, not really." Its reasons: Willen had told the accountant about the acquisition, down to the date; the goodwill was on the books; goodwill amortization (Section 197 of the US tax code) is basic knowledge for any accountant who handles business acquisitions; and it is routine treatment, not a rare exception. Source: Alex Willen, The Automated Operator

Reference 03sahn44, a Hacker News user who owns two rental properties

A Claude project caught errors in the depreciation on two rentals and the basis in a retirement account. The accountant apologized and fixed them

sahn44 had filed for an extension in April and was getting ready to file in October. With the return and all the supporting documents in a Claude project, two major issues and four minor ones came up, and sahn44 wrote that they were "all legit." The cost basis and depreciation for the two rental properties were badly off, and so was the calculation of the basis in an IRA, the after-tax money already contributed. Fixing both worked strongly in sahn44's favor.

sahn44 wrote that it felt a little awkward sending the accountant one problem after another. According to sahn44, the accountant apologized and fixed them: "he was apologetic and corrected."

How people reacted

What people liked

“I keep all my tax documents on my computer. This morning I connected Claude and ChatGPT to the folder and asked it to review my tax returns. It found errors in 4 out of the 5 years.”
The post doesn't say what the errors were or whether amended returns were filed.
Sebastián(@gvtcontractor) · Xx.com
“Went phenomenally well for me! They were apologetic, changed everything they got wrong and added some forms they missed and filed and I felt simultaneously way more assured about the process and also way more concerned about the glaring errors they missed”
intenex had a tool called Astra audit the return their accountant prepared. The original post doesn't say what Astra is or how intenex is connected to it. "They" refers to the accountant.
intenex · Hacker Newsnews.ycombinator.com
“i did this with opus5.5 this year and it caught an 8000$ mistake. Obviously i should find a new CPA, but i have found it incredibly helpful.”
A reply about using AI to review an accountant-prepared return. It doesn't say what the mistake was.
cjonas · Hacker Newsnews.ycombinator.com
“I have learned more about bookkeeping and taxes from doing them with Claude in the last few months than I have learned from my bookkeeper and CPA in the entire time I've worked with them.”
Alex Willen · The Automated Operatortheautomatedoperator.substack.com
“This is a no brainer use case for me going forward.”
sahn44 · Hacker Newsnews.ycombinator.com

What fell short

“One downside is that it will likely also flag a bunch of "by the book" libilities to how your filing that I'm pretty sure most CPA would let slide.”
cjonas · Hacker Newsnews.ycombinator.com
“I have another friend who sent so many corrections to his CPA his CPA sent him a pissed off reply telling him basically never to do that again so ymmv”
intenex · Hacker Newsnews.ycombinator.com
“But I had to feed in a ton of personal information for that to work”
weird-eye-issue · Hacker Newsnews.ycombinator.com
“Did you redact your ssn and PII info before feeding it to Claude? … Can it ever get leaked?”
sizzle · Hacker Newsnews.ycombinator.com
“I'm super wary of feeding my tax returns to an LLM.”
juicypeach · Hacker Newsnews.ycombinator.com
“I'm not in the least bit surprised it found problems. I don't think one even needs a frontier model.”
Posted to make the point that mistakes by tax preparers are common to begin with.
BeetleB · Hacker Newsnews.ycombinator.com

How to start

Gather the return your accountant prepared and the supporting documents as PDFs and upload them to a Claude project (free accounts can create up to 5). Or open that folder in Claude Code or Cowork (where Claude works with the files on your computer; paid plans). Then paste in the prompt below. Before uploading, black out sensitive numbers such as your Social Security number (SSN).

Starter prompt
Read https://www.working-ref.com/en/library/ai-tax-return-review-2026-10 and help me review my tax return. Open every return and supporting document here without skipping any, check whether the numbers on the return match the documents, and find any missed deductions or calculation errors. If there are files you couldn't read or steps you skipped, tell me first. Before you start, look at my documents and suggest three reviews worth doing first. If I pick one, start right away. If I don't pick, start by checking the whole return against the documents.

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