A computer system is provided for selecting an asset allocation for an investment portfolio intended to produce a target payout starting at a target date. The computer system is programmed to receive inputs that may relate to the target payout, the target date and a nominal rate of contributions to the investment portfolio. The computer system calculates a plurality of simulated investment outcomes based on assumed investment return rates and assumed inflation rates. The assumed investment return rates and assumed inflation rates are randomly selected in multi-year clusters from historical data. The computer system selects the asset allocation based on relative performance of the assumed asset allocations in the simulated investment outcomes.