FG estimates are just that - estimates. They are based on the rated attenuation range for the yeast, which is really just a way to compare it to other yeasts. There are too many factors in your ingredients and process to give a real FG value based on a recipe.
I didn't think ProMash did FG or ABV estimates. The only thing I see is an ABV value based on your recorded actual FG which you need to enter manually (under the Fermentation tab of the Session screen). If you are using something like lactose and want to take that into account for an estimate, you can increase your FG value in the Fermentation screen by the same number of points that the lactose contributes.