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 at least one thousand 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.