1. A computer-implemented method for selecting an asset allocation for an investment portfolio intended to produce a retirement income payment starting at a retirement date, the method comprising: identifying, by a computer system, information identifying the retirement income payment, the retirement date, and a nominal rate of contributions to the investment portfolio; calculating, by the computer system, a plurality of simulated investment outcomes, said simulated investment outcomes based on assumed asset allocations, assumed investment return rates, and assumed inflation rates, said assumed investment return rates and assumed inflation rates selected in time-based clusters from historical data concerning inflation rates and investment returns; and selecting said asset allocation based on relative performance of said assumed asset allocations in said simulated investment outcomes.