One of our Premium Features is Formulas. With the Formulas tool, you can take the information that's been added to a process through a Collect Information step and manipulate it with math. For example, you might want to calculate the cost of a building permit based on the size of the square footage of a building, or you might want to add up multiple numbers to create a total amount.
You access the Forumulas tool from the "More" section on the Edit pane of a Template.
Once you open it up, you create a name for your new formula, then add in field data and mathematical operators ( +, -, x, / ) to get the number you're looking for. Soon, we'll be launching the option to use formulas in other formulas (nested calculations).
You're only able to use required fields in Formulas, if a field is marked "optional" it won't show up in the list of choices to use as terms in your formula, so be sure that any numbers you wish to use are set up as Required fields.
Check out this video overview of setting up formulas (and how to use them in Payment steps):