How to do your Self Assessment with AI (UK)

You cannot hand your UK Self Assessment to a chatbot. Ask a general AI like ChatGPT or Claude to work out your tax and it will cite the wrong rates, invent HMRC rules, and in one 2025 tax tribunal it fabricated case law that did not exist. A return is your legal responsibility, so getting it wrong because an AI guessed is not a risk worth taking.

That is the honest version of “AI can’t do your tax return”, and it is true for the part that matters - computing and filing. But there is a different, safe use of AI that quietly removes most of the pain: keeping your income and expenses organised all year, and prepping your figures so that filing is a review, not a reconstruction. This guide covers that method. Corey is the worked example throughout - an AI operating system that runs the bookkeeping so you, or your accountant, only have to check and submit.

Do you even need to file?

You must send a Self Assessment return for the 2025 to 2026 tax year if you were self-employed as a sole trader and earned more than £1,000 (before deducting costs), were a partner in a business partnership, owed Capital Gains Tax, or had to pay the High Income Child Benefit Charge. Some company directors and people with untaxed income - rent, savings, foreign income - also need to file.

If your self-employed income was £1,000 or less, the trading allowance usually means you do not need to file at all. The first job of any AI keeping your books is to watch that threshold and tell you which side of it you are on, so you are not filing when you do not need to - or missing it when you do.

Why a general chatbot is the wrong tool for the return itself

The failure is not that AI is careless - it is that a general chatbot is built to sound right, not to be right about UK tax. It has been shown to quote incorrect tax rates, make up passages from HMRC manuals, and invent tribunal cases. HMRC’s own “Ask HMRC” assistant exists precisely because general models draw on a broad blend of outdated and incorrect content, while HMRC’s answers are pulled only from government guidance.

So the rule is simple: never let a general AI compute or file your return. That does not mean AI has no place in Self Assessment. It means you point it at the part it is genuinely good at - organising the records the return is built from.

Keep clean records all year

Self Assessment goes wrong in January because the figures are being rebuilt from memory, bank statements, and a folder of receipts. The fix is to never let the records fall behind in the first place.

Corey logs every payment in and out as it happens, attaches the receipt, categorises it - sales income, allowable expense, personal, or “ask me” - and keeps a running total of profit for the year. Nothing is reconstructed, because nothing was ever allowed to drift. By the time the deadline comes round, the numbers already exist.

See this in detail in run your freelance finances with AI.

Prep the SA103 figures for your review

The self-employment part of your return is the SA103 supplementary page, filed alongside the main SA100. It reports your turnover and your expenses. There are two versions - SA103S (short) and SA103F (full) - but both need the same thing from you: clean totals.

Because the categorising has happened all year, Corey can assemble those totals into a plain summary - income, expenses grouped by category, and the profit that follows - that you can read line by line. This is the moment the objection flips. A general chatbot guessing your tax is reckless; a structured system handing you organised figures to check is just good bookkeeping. It is preparing the return for a human, not pretending to be one.

Set the tax money aside before it is due

The tax you owe for 2025 to 2026 is due by 11:59pm on 31 January 2027, and the online return is due the same night. If your bill is over £1,000 you will usually also make payments on account - one by 31 January and a second by 31 July - each an advance on next year’s bill. A paper return, if you file that way, is due earlier, by 31 October 2026. And if you are new to Self Assessment, you must register with HMRC by 5 October 2026 to get your Unique Taxpayer Reference in time to file.

The bill should never be a shock. Corey estimates what to set aside from each payment you receive and parks it, so when 31 January arrives the money is already waiting rather than being found.

Review and submit - the line AI does not cross

This is where you take over, deliberately. You - or a qualified accountant - review the prepped figures, confirm what is genuinely allowable, and submit the return through your HMRC online account. For anything beyond a simple return, an accountant should own it; using AI to keep clean records does not replace them, it means they receive organised numbers instead of a shoebox and can do the job faster and cheaper.

None of this is tax advice, and Corey does not file for you. The whole point is the split: AI does the year-round legwork; a human owns the return.

Start with Corey

The honest promise is not “AI does your tax return”. It is that you never face a blank January again - because the records were kept, the figures were prepped, and the money was set aside, all year, without you having to remember.

Ready to try it? Start with Corey - the first 28 days are on us, no card.