Approximate formula for yield-to-maturity
nIf a bond is selling at par, yield = coupon rate.  If the bond sells at a discount, yield > coupon rate.  Hence the following approximation:
n                                   
If the bond sells at par, the approximation is exact. If it sells at a discount, the second term in the numerator is positive, and the approximation is greater than the coupon rate as desired.