The following formula is involved in the calculation of the amount of life insurance needed:

Amount of life insurance:
where I is a person's annual gross income and M is the income multiplier.

The following references can be used to cite this life insurance adequacy calculator:
 Soper, D.S. (2017) "Life Insurance Adequacy 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. 