While the per unit over modifier is most requested for use with square footage calculations it actually also can be used for mileage or really any numeric based modifiers including custom fields.
How do I set this up?
In your Services & Fees page under the Modifiers section for any service or add-on there is a new modifier type that shows up when the modifier selected is a numeric field. The type name is Per Unit Over.
Simply select this type and enter in the square footage amount over which you want to start charging per unit and add in the Fee and Hours as appropriate. Keep in mind that the calculations for this only consider the amount over that defined number.
Example:
If the property is 3500 sq ft and the amount entered in the modifier is 3000 then the modifier fee would be $50 (500*$0.10).
You are able to use this in combination with Ranges if preferred.