I have been trying to create a formula that calculates VAT costs based on the status of a checkbox.

I have 4 fields in the module....

VAT - This is the checkbox that indicates VAT is applicable

Amount - This is the base amount of the order

Total VAT - this is the cost of VAT based on the Amount field

Total - This is the Amount + Total VAT

I keep getting ' Incorrect number of arguments ' Although it's very possible I'm approaching this completely the wrong way. Here's me trying to calculate the Total VAT based on the VAT checkbox.....

If(${Adsales.VAT}, ${Adsales.Total VAT}= (${Adsales.Amount}/100)*20)

Any ideas?