As of 13 August 2026, AI cannot calculate your Capital Gains Tax.

What to actually do

1. Hand it to a person

   The route this page recommends

   Someone with a licence or accountable authority has to sign this before it counts.

2. Use a tool built for this

   Second choice

3. Do it yourself

   The distant third

   A chat interface gets you a draft, but you cannot verify it yourself. That is the catch.

   How to actually do it

   1. Open the relevant Capital Gains Tax guidance on GOV.UK and note the tax year for which you need the calculation.
   2. Gather contracts, broker statements, completion statements, invoices and bank records for every disposal and acquisition.
   3. Make a transaction table with the asset, ownership, date acquired, date disposed of, quantity, purchase amount, sale amount, fees, currency and any related facts.
   4. Paste the table and the prompt into a chatbot, asking it to separate arithmetic from uncertain UK tax treatment and to cite any current GOV.UK rule it uses.
   5. Compare every input in the response with the original documents, and correct any missing dates, costs, quantities or ownership details before asking for a revised provisional calculation.
   6. Send the documents, the calculation and every flagged uncertainty to a UK tax adviser or accountant before using the result in a return or payment to HMRC.

   Prompt

   Help me prepare a provisional UK Capital Gains Tax calculation from the records below. This is not professional advice and must not be treated as a final figure for HMRC.
   
   Use only the figures I provide or figures from current GOV.UK guidance that you identify with a direct link. Do not guess, fill gaps or assume that a relief, exemption or special rule applies. First list every missing fact that could change the result. Then calculate each disposal separately, showing proceeds, allowable purchase cost, directly related costs, and the resulting gain or loss. Keep the original currency and state any exchange-rate assumption needed. Identify possible complications such as pooled shares, gifts, inherited assets, transfers between spouses or civil partners, residential property, business assets, connected parties, or assets held jointly. Clearly separate arithmetic from questions about tax treatment.
   
   Show the calculation in a table. State which parts I can check against my records and which parts need a UK tax adviser or accountant. Do not give a final filing figure unless every required fact and the applicable current GOV.UK rule are confirmed.
   
   Tax year: [tax year]
   Asset type: [asset type]
   Transaction records:
   [paste dates, quantities, purchase prices, sale prices, fees, ownership details and supporting notes]
   Other relevant facts:
   [paste facts about residence, previous disposals, losses, reliefs, gifts, inheritances or jointly owned assets]

   Open it prefilled in ChatGPT or Claude, or copy it into Gemini, which takes no prefill link.