 Valuation of an annuity is calculated as the actuarial present value of the annuity, which is dependent on the probability of the annuitant living to each future payment period, as well as the interest rate and timing of future payments.Life tables provide the probabilities of survival necessary for such calculations.With a "single premium" or "immediate" annuity, the "annuitant" pays for the annuity with a single lump sum.