Need to calculate VAT in form if applicable

Question

I have created a form for expenses that has a field for VAT calculation. I want to calculate the VAT that applies to other fields within the form e.g. Entertainment, but only if this applies. Another field within the form indicates with Y or N whether VAT is applicable. I assume that this requires a Custom Calculation Script but as I am new to this I have not been able to come up with a script that does what I want. Any help will be appreciated.    

Answer 1

The custom calculation script for the field that calculates the VAT could be something like:
(function () {
    // Get the total amount field value
    var total = getField("Entertainment").valueAsString;
    // Get the value of the check box. This will be "Off" if it's deselected.
    var vat_applies = getField("doVAT").value;
    // Set the tax rate here. I'm using 20% as an example
    var VAT = .2;
    // Calculate the VAT if the field is not empty and the VAT should be applied
    // Otherwise, blank this field
    event.value = (total && vat_applies !== "Off") ? util.printf("%.2f", +total * VAT) : "";
This rounds the calculated value to two decimal places, but you can change that to suit your needs. Change "Entertainment" and "doVAT" in the getField lines above to match the name of the field on your form that contains the total value and the check box that indicates whether the VAT should apply.  Also, change the rate to match the actual rate. If the form is not set up the way I'm assuming it is, post again with more information.