It's unusual to have a rate change in the middle of a VAT period, and Revenue have issued guidance as to how the change is to apply. Like most VAT issues, the change appears trivial – until you start to think about it.

In applying the VAT change, there are two matters in particular to be taken into account – whether the trader accounts for VAT on the invoice or the cash receipts basis, and whether the customer is a business customer or an unregistered consumer. While very broadly, VAT should be charged at the rate applicable at the date of issue of the invoice, issues can arise in relation to credit notes and periodic payments.

The Revenue commentary is reproduced at Section 2.03.