This article aims to quantify the aggregate subjective economic risk to which beneficiaries would be exposed if a retirement pension system based on notional account philosophy were introduced. We use scenario generation techniques to make projections of the factors that determine the real expected internal rate of return (IRR) and the expected replacement rate (RR) for the beneficiary according to six retirement formulae based on the most widely accepted rates or indices. We then apply the model to the case of Spain. Our projections are based on Herce and Alonso's macroeconomic scenario 2000–2050 (2000) and include information about the past performance of the indices and the time period the forecast is to cover. The results of the IRR calculation—average value, standard deviation, and value-at-risk (VaR)—are analyzed both in objective terms and for different degrees of participants' risk aversion.