SEBI has done the categorisation of most types of mutual funds based on Macaulay duration. Macaulay duration is the measure of how long it takes for an investor to get back the money they invested (price paid) in a bond with its cash flows (periodic interest repayments and principal repayment). Measured in years, the Macaulay duration of a debt mutual fund scheme is the weighted average Macaulay duration of the debt securities that the scheme holds in its portfolio.