Hi Marcos:

Setting the discount % to -20 is the right way to do it. Think of it as markup/markdown instead of discount.

I'm assuming you have selected Compute Price = Formula and Based On = Cost like the example below.

I could get desired output price by setting a negative discount.

for example if i want to charge 20% based on cost, in formula i have to set -20 in discount.

it works but i would like something more robust.

thanks