Convert the VAT rate from a percentage to a decimal by dividing it by 100. Since the VAT rate in Ireland is 21 percent, in decimal form this is equal to 0.21.
Add the VAT rate in decimal form to 1 in order to calculate VAT reductions. This value is now 1.21.
Note the price of a purchased good. This can be found on a receipt if it has already been purchased, or on a sticker located on or around the good if it has not been purchased.
Compute the price of the good without VAT by dividing the price of the product by the value 1.21.
For example, say a t-shirt costs €12.10. To calculate its worth before VAT, divide €12.10 by 1.21 (€12.10/1.21) to obtain a value of €10. The original price of the t-shirt, before VAT, is €10.
