The following formula is involved in the calculation of current yield values for bonds:

Current yield (simple yield) of a bond:
where I is the annual interest payment received by the bond holder and P is the market price of the bond.

The following references can be used to cite this current yield of a bond (simple yield) calculator:
 Soper, D.S. (2018) "Current Yield of a Bond (Simple Yield) 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. 