Holding all other maturities constant, this measures the sensitivity of a security or the value of a portfolio to a 1% change in yield for a given maturity.

The calculation is as follows:



Where:
P- = Security's price after a 1% decrease in yield 
P+ = Security's price after a 1% increase in yield 
P0 = Security's original price 



|||There are 11 maturities along the Treasury spot rate curve, and a key rate duration is calculated for each. The sum of the key rate durations along a portfolio yield curve is equal to the effective duration of the portfolio.