Start with the document details
For a standard full VAT invoice, review the unique invoice number, supplier details and VAT registration number, customer details, invoice date and supply date. Describe the goods or services clearly, with the relevant quantities, prices, rates and totals. Different invoice types have different requirements; consult Notice 700.
Check the arithmetic separately
Multiply quantity by unit price, apply the agreed discount, then calculate VAT on the appropriate net line. Reconcile the net total plus the VAT total to the final amount due. Separate mixed-rate items rather than forcing one rate onto the whole invoice.
A practical example
Two net lines of £80 and £50, both at 20%, produce £16 and £10 VAT. Total net is £130, VAT is £26 and gross is £156. If a customer queries £156, you can show both the quantity calculation and the tax calculation rather than only a final total.
Before you send
Verify customer and supplier details against your records. Check special wording or treatment where relevant, and retain the final document. The calculator creates figures only; it does not generate a compliant invoice or validate a VAT registration number.
Keep learning
Official sources
Sources checked: 2026-09-26. Check the official guidance for later changes.
Educational information and estimates. These tools do not submit VAT returns or determine the treatment of a specific transaction.