As of 13 August 2026, AI can only partly calculate VAT on your UK construction invoices.

What to actually do

1. Hand it to a person

   The route this page recommends

   A person who owns the outcome does this end to end, worth it when the failure is dear.

2. Use a tool built for this

   Second choice

3. Do it yourself

   The distant third

   A chat interface, chat-fluent skill, and roughly 30 minutes until you can act on the result.

   How to actually do it

   1. Open the relevant HMRC and GOV.UK guidance on VAT for construction services, including the domestic reverse charge, and keep the pages available for comparison.
   2. Gather the invoice date or tax point, your VAT registration details, the customer’s VAT status, whether the customer is the end user or an intermediary, and a plain description of each construction service.
   3. Copy each invoice line into a spreadsheet with the description, quantity, unit price, discount, net amount and any VAT already charged, removing bank details and other unnecessary private data.
   4. Paste the business details and spreadsheet lines into the prompt, then ask the chatbot to produce the line-by-line VAT table and list unresolved facts.
   5. Compare each proposed VAT treatment and linked HMRC source with the construction work and customer facts, and mark any line where the source does not clearly apply.
   6. Recalculate the net, VAT and gross columns in your spreadsheet and compare the totals with the chatbot's arithmetic.
   7. Send the uncertain lines, source links and calculations to your accountant before issuing the invoice or including the figures in your VAT records.

   Prompt

   I need to calculate VAT for UK construction invoices. Use only the information I provide and current HMRC or GOV.UK guidance that you can identify. Do not guess, and do not treat this as professional advice.
   
   Business details:
   - VAT registration status: [insert]
   - VAT accounting scheme, if known: [insert]
   - Work carried out: [describe the construction services and property or project]
   - Customer type and VAT status: [insert]
   - Whether the customer is the end user or intermediary: [insert]
   - Whether the work may fall under the domestic reverse charge: [insert or unknown]
   - Invoice date or tax point: [insert]
   
   Invoice lines:
   [paste each line with description, quantity, unit price, discount, and any VAT already shown]
   
   For each line, produce a table showing the net amount, proposed VAT treatment, VAT rate, VAT amount and gross amount. Separate arithmetic from the decision about the VAT treatment. Identify every missing fact that could change the result, flag any line that needs an accountant's review, and show the calculation in a way I can reproduce in a spreadsheet. Link to the relevant GOV.UK or HMRC guidance for each non-standard treatment. If the facts do not establish the treatment, say that you cannot determine it rather than selecting a rate. Do not prepare or submit a VAT return.

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