Question: how to calculate percentage of vat?
Answer: Take the gross amount of any sum (items you sell or buy) – that is, the total including any VAT – and divide it by 117.5, if the VAT rate is 17.5 per cent. ... 
Multiply the result from Step 1 by 100 to get the pre-VAT total.
Multiply the result from Step 1 by 17.5 to arrive at the VAT element of the bill.