In the case of transactions with other VAT registered persons, a person accounting
for VAT on the sales or invoice basis must apply the rate of VAT in force at the time
they issue, or are obliged to issue, an invoice.
In the case of transactions with
persons who are not registered for VAT, an accountable person must apply the VAT
rate in force at the time of the supply.
Persons accounting for VAT on the basis of moneys received, must apply the rate of
VAT in force at the time of the supply.
VAT invoices issued by a VAT registered person to another VAT registered person on
or after the date of change of a VAT rate(s), either upwards or downwards, should
show VAT at the new rate(s). This applies even if the goods or services were supplied
before the date of the change.
Any credit note relating to a supply of goods or services which contains a VAT
adjustment and which is issued to a VAT registered person on or after the date of a
change in a VAT rate(s), should show VAT at the rate in force at the time the original
invoice issued.
Source: revenue.ie
