A computer-implemented method, system, and apparatus for managing investment savings of individuals through an investment vehicle suitable for retirement, estate or general investment planning. The invention establishes the mechanics of the operations to create an open-end investment fund as a means for individual participants to earn both market returns on their investments and demographic returns (DR) on the actual demographic experience of the pool of investors who participate in the investment fund. Individuals can invest in the fund and make additional deposits and withdrawals at any time. Investors specify a payout schedule, and those who sell their investments, as scheduled, earn full returns, combining market returns and the DR. Investors who make unscheduled withdrawals from the fund, receive lower returns. The investment fund is customized, and administered by computer software that is available to both participants in the fund and to asset managers who offer the fund to investors.