How do I calculate VAT on my invoices?

To add VAT to a net price, multiply by 1.20 for the standard 20% rate (so £100 becomes £120). Your VAT invoice needs to show your VAT registration number, the net amount, the VAT rate applied, the VAT amount, and the gross total, and it must be issued within 30 days of the supply for most transactions. Most accounting software will calculate and display this automatically once you set it up as VAT registered, which reduces the risk of manual errors.