How to calculate the YTW
For some bonds, the yield to worst is the same as the yield to maturity, but on callable bonds, it may be the same as the yield to call. It’s always the lowest of either the yield to call or yield to maturity. These formulas are below:
YTC = ( coupon interest payment + ( call price - market value ) / number of years until call) / (( call price + market value ) / 2 )
YTM = ( coupon interest payment + (( face value - present value ) / years to maturity ) / (( face value - present value ) / 2 )
Simply choose the worst outcome and that’s the yield to worst. Pretty simple, but it’s important to note that you don’t have to do this for zero-coupon bonds, since you’re not looking to account for missed interest payments.