Macaulay duration

In finance, duration is the weighted average maturity of a bond's cash flows or of any series of linked cash flows. Then the duration of a zero coupon bond with a maturity period of n years is n years. If there are coupon payments, the duration will be less than n years. This measure is closely related to the derivative of the bond's price function with respect to the interest rate, and some authors consider the duration to be this derivative divided by the price, with the weighted average maturity simply being an easy method of calculating the duration for a non-callable bond. It is sometimes explained in inaccurate terms as being a measurement of how long, in years, it takes for the price of a bond to be repaid by its internal cash flows.
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The weighted-average term to maturity of the cash flows from the bond, where the weights are the present value of the cash flow divided by the price.