Analytic solution for ratchet guaranteed minimum death benefit options under a variety of mortality laws

We derive a number of analytic results for GMDB ratchet options. Closed form solutions are found for De Moivre's Law, Constant Force of Mortality, Constant Force of Mortality with an endowment age and constant force of mortality with a cutoff age. We find an infinite series solution for a general mortality laws and we derive the conditions under which this series terminates. We sum this series for at-the-money options under the realistic Makeham's Law of Mortality.