The following formula is involved in the calculation of costs of a discount:

Cost of a discount:
where D is the discount percentage, C is the percentage of customers expected to capitalize on the discount, and ACS is the company's annual credit sales.

The following references can be used to cite this cost of a discount calculator:
 Soper, D.S. (2017) "Cost of a Discount Calculator (Online Software)", http://www.danielsoper.com/fincalc. 
 Siegel, J. and Shim, J. (1997). "Schaum's Quick Guide to Business Formulas", New York, NY: McGrawHill. 