Can AI do my company tax return? ChatGPT and CT600 FAQs

In short: An AI chatbot can't file your Company Tax Return (CT600) on its own. ChatGPT, Claude, Gemini and Copilot can explain the rules and help you prepare, but since 1 April 2026 returns go to HMRC through commercial software (GOV.UK: closure of HMRC's filing service), and the company stays responsible for every figure.

Start your return, or take the 30-second check to see whether Taxley fits your company.

Key facts (checked on 30 September 2026)

Can ChatGPT do my company tax return?

Not on its own. ChatGPT, Claude, Gemini and Copilot can explain Corporation Tax rules and help you prepare, but a chatbot isn't filing software and doesn't take on the company's responsibility. Since 1 April 2026, HMRC expects companies to file the CT600, computation and accounts through commercial software (GOV.UK: closure of HMRC's filing service).

A Company Tax Return is more than one form. HMRC needs the CT600, a Corporation Tax computation and the company's accounts, with the accounts and computation in iXBRL, an IT standard designed for business financial reporting (HMRC manual COM60040). A general AI assistant works with text. It can explain what a box means, why taxable profit differs from the profit in the accounts, or when the return is due. It sees only what you paste into it, so it can't tell whether the company's records are complete, and it doesn't sign the declaration. Directors stay legally responsible for the company's records and accounts even when someone else helps with them (GOV.UK: running a limited company). The table below sorts common company tax tasks by how far a director can safely hand each one to an AI assistant, and what to check when you do.

Can AI file my CT600 with HMRC?

No, not a chatbot on its own. HMRC's own online filing service closed on 31 March 2026, and returns now go through commercial software (GOV.UK: closure of HMRC's filing service). Filing software can include AI features, but HMRC expects generative AI in tax software to support, not replace, human judgment (HMRC: generative AI guidelines).

HMRC published its guidelines for software developers using generative AI on 28 January 2026 (HMRC: guidelines for using generative AI). They expect AI-enhanced tax software to tell users that it uses generative AI, draw on reliable sources such as HMRC publications and legislation, prompt users to check its results, and let them correct errors. Where a question involves nuanced rules or a complex scenario, the software should flag it and point to further investigation or advice from a qualified tax professional. It should also remind users that making sure their tax returns are accurate is their own responsibility. AI agents that operate a web browser for you raise a separate problem. To file a return, an agent of that kind would need the company's Government Gateway sign-in details, and GOV.UK says you must not share those with anyone, including your tax agent (GOV.UK: keeping your HMRC sign in details safe). So the submission should come from the director, or from an accountant using their own agent sign-in details, not from an AI tool.

Who is responsible if AI gets my tax wrong?

The company and its directors, not the AI tool. GOV.UK says directors stay legally responsible for the company's records and accounts even with hired help (GOV.UK: running a limited company), and a careless error in a Company Tax Return can cost the company a penalty of up to 30% of the potential lost revenue (FA 2007 Sch 24 para 4).

Schedule 24 to the Finance Act 2007 charges a penalty when a document such as a company tax return contains an inaccuracy that understates tax or inflates a loss or repayment claim, and the inaccuracy was careless or deliberate (FA 2007 Sch 24 para 1). Careless means failing to take reasonable care. HMRC's factsheet on these penalties puts a careless error in the range 0% to 30% for an unprompted disclosure and 15% to 30% for a prompted one (HMRC factsheet CC/FS7a). The factsheet doesn't mention AI, but its rule on help from others is plain: if you ask someone else, such as an employee or adviser, to do something for you, you must do everything you reasonably can to prevent any inaccuracies. An answer from an AI assistant needs at least the same checking before it goes into the return. Keeping a short note of what you checked, and where, also helps you show the care you took if HMRC asks questions later.

Can AI prepare my company accounts or iXBRL?

AI can help you understand and draft accounts, but approving and filing them isn't its job. The board must approve the annual accounts and a director must sign the balance sheet (Companies Act 2006 s.414), and HMRC needs the accounts and computation in iXBRL (HMRC manual COM60040).

A chatbot is useful for the concepts: what a micro-entity balance sheet shows, what an accrual is, or why a director's loan appears in the accounts. It can't tell whether the bookkeeping is complete, because it works only from what you paste in. iXBRL is an IT standard designed specifically for business financial reporting, and HMRC requires it for the accounts and computations in an online Company Tax Return (HMRC manual COM60040). The figures have to carry the right tags from a published taxonomy, so the file needs producing and checking with software built for the job, not copying from a chat window. The legal stakes sit with the directors. A director who knows that the accounts being approved don't comply with the Companies Act, or is reckless about it, and fails to take reasonable steps to secure compliance or prevent their approval commits an offence (Companies Act 2006 s.414). Our guide on why HMRC needs iXBRL rather than PDF accounts explains the format in more detail.

Can I use AI to check my Corporation Tax figures?

Yes, as a second pair of eyes, but don't take its numbers on trust. The main rate of Corporation Tax is 25%, the small profits rate is 19% for profits of £50,000 or less, and marginal relief applies between £50,000 and £250,000 (GOV.UK: Corporation Tax rates). Recompute any AI figure against those rules.

AI answers can be out of date, and recent changes are easy to miss. The main rate of writing down allowance on plant and machinery changed from 18% to 14% on 1 April 2026 for Corporation Tax (GOV.UK: capital allowance rates and pools), so an assistant relying on older material may still quote 18%. Quick answers also skip details. The £50,000 and £250,000 limits are proportionately reduced for an accounting period shorter than 12 months and by the number of associated companies (GOV.UK: marginal relief), which can change the tax on the same profit. Give the assistant your accounting period dates and the number of associated companies, ask it to show its working and name its source, then recompute the tax with the Corporation Tax calculator. Our guide on how to calculate Corporation Tax walks through marginal relief step by step, so you can see where an AI figure went wrong.

Is it safe to put company data into ChatGPT?

Only if you leave sensitive details out. The National Cyber Security Centre has advised against including sensitive information in queries to public chatbots, because the organisation providing the service can see them (NCSC: ChatGPT and large language models). If a prompt contains personal data, such as a director's details, UK GDPR's principles apply (UK GDPR Article 5).

Personal data is any information relating to an identified or identifiable person, such as a name or an identification number (UK GDPR Article 4). The ICO says that if you use AI to process personal data, you need to comply with the principles of data protection by design and by default (ICO: guidance on AI and data protection). UK GDPR also requires personal data to be limited to what is necessary for the purpose, and most tax questions need none at all. In practice, never paste Government Gateway sign-in details into a chatbot. Leave out the company's UTR, bank details, National Insurance numbers, home addresses and dates of birth, and ask about the rule with round or made-up figures rather than the real ledger. Before using a chatbot for company work, read the provider's privacy settings to see whether chats are kept or used to train its models, and choose the most private option that still does the job.

Should I give an AI tool my Government Gateway password?

No. GOV.UK says you must not share your HMRC sign in details with anyone, including your tax agent, and warns that someone using them could steal from you and HMRC (GOV.UK: keeping your HMRC sign in details safe). Treat chatbots, browser extensions and AI agents the same way, and never type or paste the password into them.

Filing software is a different case, because it typically submits the return to HMRC with your own credentials at the moment you file. HMRC's Self Assessment guidance, for example, tells you to enter your Government Gateway user ID and password into the relevant fields of your commercial software when you submit (GOV.UK: submitting a Self Assessment return with commercial software). An accountant doesn't need your sign-in details either. GOV.UK tells agents to access client details through their own agent registration and not to use their clients' sign in details (GOV.UK: keep your HMRC online security information safe as an agent). If a chatbot or AI agent offers to sign in to HMRC and file for you, it's asking for exactly the details GOV.UK says to keep to yourself. Keep the password in a password manager, not in a chat history.

Is AI accounting software safe for a UK limited company?

It depends on the product. HMRC's guidelines for tax software that uses generative AI give a useful test: the software should tell you it uses generative AI, rely on official sources, prompt you to check its results and remind you that the accuracy of your return is your responsibility (HMRC: generative AI guidelines).

Use HMRC's guidelines as a checklist when a product advertises AI features. Ask whether it flags nuanced rules or complex situations and recommends a qualified tax professional when one is needed, whether you can see and correct each figure before anything is sent, how it applies human review to the model's output, and how it protects your data under UK GDPR, which the guidelines expect it to comply with (HMRC: generative AI guidelines). Then check the basics any CT600 software must cover. HMRC's guidance says the software you choose should let you file a CT600, a Corporation Tax computation and your company accounts (GOV.UK: closure of HMRC's filing service). Also ask whether it files the accounts at Companies House, which kinds of company it supports, and how it signs in to HMRC. Our guide to whether cheap CT600 software is safe has a fuller checklist that applies whether or not a product uses AI.

Does HMRC use AI?

Yes, for its own work. HMRC's 2026 roadmap update says it is piloting AI call summarisation and had issued over 28,000 Microsoft Copilot licences to staff by March 2026 for tasks such as drafting and summarising. It says Copilot will also support compliance work, always with skilled caseworkers making final decisions (GOV.UK: HMRC Transformation Roadmap update 2026).

HMRC's Transformation Roadmap progress update, first published on 2 July 2026, also describes interactive AI simulators that let customer service staff practise realistic customer conversations, and work on how AI can make HMRC's digital assistant more conversational (GOV.UK: HMRC Transformation Roadmap update 2026). Separately, HMRC published guidelines in January 2026 setting out what it expects from software developers who add generative AI to products that help customers send information to HMRC (HMRC: generative AI guidelines). Those guidelines ask software to remind users that the accuracy of their tax returns is their responsibility. HMRC's own use of AI doesn't change the director's position either: the company still prepares, checks and files its return, and still answers for the figures in it, whichever tools helped along the way.

Can AI replace an accountant?

Not for judgement or accountability. An accountant or tax adviser can be authorised to deal with HMRC for your company (GOV.UK: appoint someone to deal with HMRC) and must be supervised for money laundering purposes, and a chatbot can be neither. Whether you need an accountant depends on your company, not on AI.

An accountant brings judgement on your facts, asks the questions a chatbot won't know to ask, and can act as the company's agent with HMRC. Accountancy service providers must register with HMRC for money laundering supervision unless a professional body already supervises them (GOV.UK: money laundering supervision for accountancy service providers). HMRC's own guidelines expect AI tax software to flag nuanced rules or complex scenarios and point to further investigation or advice from a qualified tax professional (HMRC: generative AI guidelines), so even HMRC treats AI as an aid to judgement rather than a replacement for it. A director can prepare and file a straightforward return with software, while a company with complex reliefs, group relationships or unusual transactions often benefits from an accountant's review. Our comparison of filing yourself and using an accountant sets out what you can do alone and when to get help.

What can AI do well for a small company?

Explaining and organising. An AI assistant can put GOV.UK guidance into plain English, summarise a long HMRC page, list the records to gather and draft questions for your accountant. It can explain, for example, why the profit for Corporation Tax differs from the profit in your annual accounts, a difference GOV.UK points out (GOV.UK: Company Tax Returns).

The best results come from giving the assistant the source rather than asking it to remember one. Paste the text of the GOV.UK page, or name it, and ask for a summary, a checklist or the questions it leaves open, then compare the summary with the page itself. Useful jobs include setting out which dates matter (the return is due 12 months after the end of the accounting period it covers, according to GOV.UK: Company Tax Returns), preparing a list of expenses to ask your accountant about, explaining a CT600 box in plain words, and turning HMRC terms into a to-do list. Keep real figures and identifying details out of the prompt where you can, and treat every output as a draft to verify. The CT600 boxes explained page and the Corporation Tax glossary are handy for checking the terms an assistant uses.

How do I check an AI answer about tax?

Treat it as a draft to verify: find the source, confirm it's current and redo the numbers. HMRC expects someone facing an unfamiliar transaction to find out the correct tax treatment or seek advice, and to draw attention to any remaining uncertainty when sending the return (HMRC manual CH81120).

1. Check the date. Ask which tax year and rules the answer uses, and compare them with your accounting period.
2. Open the source. Find the GOV.UK page, HMRC manual or legislation behind the answer, and the sentence that supports it.
3. Confirm the scope. Make sure the answer is about UK Corporation Tax for a company, not Self Assessment or another country.
4. Recompute the numbers. Use a calculator built on the published rates rather than the chatbot's arithmetic.
5. Test the exceptions. Ask whether associated companies, a short period or losses change the answer for you.
6. Ask an adviser. Get professional advice when the answer turns on judgement or involves a large sum.
7. Keep a note. Record what you checked, where and when, in case HMRC asks later.

Can AI assistants use Taxley's calculators?

Yes. Taxley (taxley.co.uk), UK online software that prepares and files the Company Tax Return (CT600) with HMRC and the annual accounts with Companies House, runs a free MCP server at https://taxley.co.uk/mcp. An AI assistant connected to it can run Taxley's calculators, which apply the rules GOV.UK publishes (GOV.UK: Corporation Tax rates), instead of estimating figures itself.

The server offers eight calculators: Corporation Tax (small profits rate, main rate and marginal relief, with associated companies and short periods), payment and filing deadlines, late filing penalties and interest (GOV.UK: late filing penalties), director's loan (s.455) tax, capital allowances, chargeable gains with indexation, micro-entity and small company size, and splitting a long accounting period into two returns. The iXBRL accounts checker works only on its web page, because it needs a file upload. The same code answers the calculator pages, a JSON API with an OpenAPI description, and the MCP server, so a figure is the same wherever it comes from. The tools need no key or account. Each IP address can make 60 API and 120 MCP requests a minute, and inputs aren't saved to an account or a database. Each result links back to the calculation on taxley.co.uk and says it's general guidance, not tax advice. The developers page shows how to connect Claude or ChatGPT, and the free tools page lists every calculator.

Filing doesn't happen through an assistant. In Taxley, the director prepares the return, reviews the CT600, computation and iXBRL accounts, confirms the declaration and files with the company's own Government Gateway user ID and password, typed in on the submission screen. Taxley uses them only to send that return, keeps the user ID encrypted and never keeps the password. Taxley's own calculations are rule-based code, not a language model, and questions sent through its help box or live chat go to Taxley's support team, not a chatbot. A return with micro-entity accounts costs £44.50 (promotion price until 31 Dec 2026; £89.00 from 1 Jan 2027), charged only when you choose to file, and you can prepare the return and preview the documents before paying anything. Taxley isn't tax advice. It doesn't handle R&D relief or VAT. It has filed annual accounts at Companies House since 28 September 2026, but not confirmation statements, which Companies House requires separately (GOV.UK: running a limited company). Take the 30-second check to see whether Taxley fits your company, then start your return with Taxley.

Frequently asked questions

Can ChatGPT work out my Corporation Tax bill?

It can try, but check the result. The small profits rate is 19% on profits of £50,000 or less and the main rate is 25% above £250,000, with marginal relief in between (GOV.UK: Corporation Tax rates). Short periods and associated companies reduce those limits, so recompute with a calculator.

Is it against HMRC rules to use AI for my tax?

No HMRC rule we found bans it, and HMRC says it encourages innovative use of AI in tax software products (HMRC: generative AI guidelines). What matters is the result: a careless inaccuracy that understates tax can bring a penalty (FA 2007 Sch 24 para 1), whatever tool produced it.

Can AI tell me my filing and payment deadlines?

It can explain the rules, but check the dates yourself. The return is due 12 months after the end of the accounting period (GOV.UK: Company Tax Returns), and a company with taxable profits up to £1.5 million pays 9 months and 1 day after it (GOV.UK: pay Corporation Tax).

Does it matter which AI assistant I use?

Less than how you use it. ChatGPT, Claude, Gemini and Copilot can all be wrong or out of date, the same caution about sensitive information applies to each (NCSC: ChatGPT and large language models), and none of them takes on the company's responsibility for its return.

What if I've already pasted my Gateway password into a chatbot?

Change the password straight away and delete the chat. If you then see activity in the company's HMRC online account that you don't recognise, GOV.UK says to report it to HMRC immediately (GOV.UK: report suspicious activity). Don't reuse that password anywhere else.

General information, not personalised tax or accounting advice.