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Plenty of people now open ChatGPT before they open their HMRC account. You type in your salary, your rental income and a few receipts. Within seconds, a neat answer appears with a tax figure at the bottom. It feels like having an accountant in your pocket. Sometimes the answer is right. However, a ChatGPT tax return answer can also be wrong in ways you will never spot. It sounds just as sure of itself either way. And when the figure on your return is wrong, HMRC holds you responsible, not the chatbot.
Below, we look at what AI does well and where it gets UK tax wrong. You will also learn how to use it without landing a penalty.
Why so many people now ask AI about their tax
The shift happened fast. In September 2025, the tax app Taxfix found that 59% of Brits planned to use AI for their tax return. Most wanted something faster, easier or cheaper than an accountant.
Accountants have noticed the effects. In December 2025, the software firm Dext surveyed 500 UK accountants and bookkeepers. Half knew of businesses that had lost money because of wrong AI advice. Meanwhile, 31% said they came across AI mistakes every week.
So people clearly use ChatGPT for their tax return already. What matters now is when you can trust it.
What ChatGPT does when you ask about your tax return
ChatGPT does not look up your tax position. Instead, it predicts the most likely wording of an answer based on the text it learned from. Most of that text is old, and a lot of it comes from the United States.
That has two consequences. First, the model can repeat rates from a previous tax year without warning you. Second, it fills gaps with whatever sounds plausible. Tax professionals call these made up answers hallucinations, and they read exactly like real ones.
Some newer versions can search the web. That helps. Still, the tool has to pick the right source, the right tax year and the right rule for you. It often gets one of those three wrong.
Five places where AI gets UK tax wrong
1. It quotes last year's rates
UK tax figures move every April, and AI training data lags behind. Here are a few changes that older answers often miss:
| What changed | Old figure | Current figure |
|---|---|---|
| Dividend tax, basic and higher rates | 8.75% and 33.75% | 10.75% and 35.75% from 6 April 2026 |
| Capital Gains Tax annual exempt amount | £12,300 | £3,000 since April 2024 |
| High Income Child Benefit Charge starts | £50,000 | £60,000 since April 2024 |
| UK property CGT reporting deadline | 30 days | 60 days since October 2021 |
| Making Tax Digital for Income Tax | “Coming soon” | Live since 6 April 2026 for income over £50,000 |
Each of these errors changes a real tax bill. For example, the dividend rise alone adds hundreds of pounds for a typical company director.
2. It answers with American tax rules
Because so much training data is American, AI often slips in US ideas. You may see talk of a “standard deduction”, “filing jointly” or a 15 April deadline. None of these exist in UK Self Assessment. For instance, married couples in the UK file separate returns, and the online filing deadline is 31 January.
3. It forgets that Scotland is different
Scotland sets its own income tax bands for earnings. Unless you say you live in Scotland, most chatbots apply the rest of the UK rates by default. As a result, a Scottish taxpayer can get a figure that is wrong from the first line.
4. It does not ask the questions an accountant would ask
A good adviser asks about the things you forgot to mention. Do you have a student loan? Does your partner claim Child Benefit? Did you pay into a personal pension? Higher rate taxpayers, for example, often need to claim extra pension relief through their return. Nobody does it for them.
ChatGPT only works with what you type. If you leave something out, it rarely asks. Consequently, the answer looks complete even when it is not.
5. It cannot take responsibility
ChatGPT cannot file your return, sign the declaration or speak to HMRC for you. More importantly, it carries no professional indemnity insurance. If it gets something wrong, the bill, the interest and any penalty stay with you.
One outdated rate, a £790 gap
Sarah runs her own limited company. In 2026/27 she pays herself a salary of £12,570 and takes £40,000 in dividends. She asks ChatGPT to check the figures for her tax return. Unfortunately, it answers using the 2025/26 rates.
Here is how the two answers compare:
| Dividend amount | Old rates (2025/26) | Correct rates (2026/27) |
|---|---|---|
| First £500 of dividends (allowance) | £0 | £0 |
| £37,200 in the basic rate band | 8.75% = £3,255.00 | 10.75% = £3,999.00 |
| £2,300 in the higher rate band | 33.75% = £776.25 | 35.75% = £822.25 |
| Total dividend tax | £4,031.25 | £4,821.25 |
The outdated answer leaves Sarah £790 short. She sets aside too little, and then a bigger bill arrives in January. Worse, if she enters the wrong figure on her return, she may face interest and a penalty on top. Our guide to salary vs dividends for directors explains how the 2026/27 rates change the best mix.
Does HMRC accept “the AI told me” as an excuse?
No. HMRC expects every taxpayer to take reasonable care. Its own penalty guidance says that even when you ask someone else to help, you must still do everything you reasonably can to avoid mistakes.
If HMRC decides an error was careless, the penalty can reach 30% of the extra tax due. Deliberate errors can cost up to 70%, and deliberate errors you try to hide can cost up to 100%. Telling HMRC about a mistake before it finds it usually brings the penalty down a long way.
Relying on ChatGPT for your tax return without checking its answers is unlikely to count as reasonable care. In contrast, relying on a qualified adviser who knew your full situation is a much stronger position.
What AI is genuinely good for
None of this means you should ignore AI. Used well, it saves time. It works best for jobs where you can check the result yourself:
- Explaining terms. Ask it what “payments on account” means before you speak to your accountant.
- Sorting records. Use it to group a year of bank transactions into categories.
- Building checklists. Ask what documents a landlord usually needs for a return, then compare it with HMRC’s list.
- Drafting questions. Prepare a clear list of questions for your adviser so your meeting goes further.
The pattern is simple. Let AI organise and explain, and let a person who knows your full picture make the decisions.
How to use ChatGPT for your tax return safely
If you do use ChatGPT or a similar tool, follow these five rules:
- State the tax year and where you live. For example, start with “UK tax year 2026/27, I live in England”.
- Check every figure on GOV.UK. Treat any rate, allowance or deadline as unconfirmed until you find it on an official page.
Never paste personal identifiers. Keep your UTR, National Insurance number and bank details out of the chat. Unless you change the settings, many AI tools can keep your conversations. - Ask it what it does not know. Prompt it to list the assumptions it made. Then check each one.
- Get a human review before you file. This matters most when you have more than one income source, rental property, capital gains or a limited company.
Why a qualified, registered adviser still matters
Since 18 May 2026, HMRC has been rolling out mandatory registration for tax advisers who deal with HMRC on behalf of clients. Advisers who miss their registration window lose the right to act for clients with HMRC. That gives you a simple check that no chatbot can pass.
A good accountant also does the work AI skips. They ask about your whole year and spot reliefs you did not know existed. Then they stand behind the return they prepare. At IBISS & CO, our Self Assessment tax return service covers everything from simple returns to landlords and directors. If you want to start on your own, our Self Assessment guide walks you through the basics.
Already used AI for this year’s figures? Book a call and we will check them before you file.
Frequently asked questions
Can I use AI for my tax return?
Yes, you can use AI to understand terms, organise records and prepare questions. However, you remain legally responsible for every figure you send to HMRC. Check all rates and allowances on GOV.UK, and ideally ask a qualified adviser to review the return before you file.
Can I trust a ChatGPT tax return answer?
Not on its own. A ChatGPT tax return answer is useful for explaining jargon, sorting expenses into categories and building a document checklist. However, it is far less reliable at working out your actual bill. It often uses old rates and misses details you did not mention, so check every figure on GOV.UK before you rely on it.
Can I claim ChatGPT on my tax return?
If you are self employed and use a paid ChatGPT plan for your business, you can usually claim it as an allowable expense. If you also use it for personal tasks, you can only claim the business share, as HMRC’s guidance on expenses if you’re self employed explains. Employees usually cannot claim it, because the rules for employee expenses are much stricter.
Do HMRC check your tax return?
Yes. HMRC runs compliance checks on Self Assessment returns. It also matches your return against data from employers, banks and online platforms. It can normally open a check within 12 months of receiving an on time return. After that, it can usually look back 4 years. For careless mistakes it can go back 6 years, and for deliberate ones up to 20.
Is it safe to give ChatGPT my financial details?
Share as little as possible. Leave out your name, UTR, National Insurance number and bank details. You can describe your situation in general terms and still get a useful explanation.
Will ChatGPT replace an accountant for my tax return?
It will change how accountants work, but it cannot sign your return, represent you to HMRC or take responsibility for advice. For anything beyond a simple question, you still need a person who understands your full situation.
This guide gives general information, not personal advice. If you are unsure whether an AI answer applies to you, speak to our team before you file.
Asim Hussain
Asim Hussain is a senior accountancy professional at IBISS & CO, having joined the firm in 2014.
He leads the accountancy team and specialises in financial planning, business growth strategies, UK accounting standards, Companies Act compliance and HMRC requirements. His experience spans a wide range of sectors, including telecoms, transport, healthcare and fashion.
Last reviewed: October 2026
