Whats the VAT? United Kingdom, adds and takes away 20% Value Added Tax. Use the Add 20% VAT Calculator to work out what the pricing is after-VAT has been added, an equation formula will be shown which reveals the value of the tax and the final price. Or alternatively use the Minus 20% VAT Calculator to work out what the value of the product was before-VAT was added. Custom after-tax and before-tax calculators included. Perfect for start-ups and businesses!