Depends on the period of deferment, the size of the payments, the length of the annuity and the interest rate. Always helpful to give a specific example. Suppose - we have annual payments of 5 starting at time 11 and finishing at time 20. \(DMT = \dfrac {5*11v^{11} +5*12v^{12} + \dots + 5*20v^{20}}{5v^{11} +5v^{12} + \dots + 5v^{20}}\)
So now for the numerator we have to solve each term separately? It will consume a good amount of time if the term of annuity is large!