Calculation in form field doubles the amount

[AnnieShand]

I’m trying to create a user form to book catering for functions. I’ve got drop down lists for menu items - all working fine.
I’ve then inserted cost fields (currency) for starter course, fish course, main course and dessert
In the next section I have a Total cost per head field which adds the above field contents - all ok
Next I have a field for number of people, then a field for extras

I now need a field to calculate #costperhead multiplied by#numberofpeople + #extras.


I typed the calculation as =(costperhead*numberofpeople)+extras but the result is double the amount it should be. Can anyone advise me how to write the calculation to return the correct value please?