1. A system operative to guarantee on a daily basis a guaranteed return by an open-ended fund on a maturity date, the fund having traditional assets that correlate to a benchmark invested in a market, comprising: a database configured to store a high-watermark value of a closing price of a share in the open-ended fund; a valuation engine comprising a processor configured by code to: quantify an aggregate net asset value (ANAV) of the traditional assets of the fund as of a current date; compute the closing price of the share in the open-ended fund as of the current date by dividing the ANAV by the number of shares; determine whether the closing price of the share as of the current date is higher than the high-watermark value in the database, and, if the closing price is higher than the high-watermark value in the database: selectively reset the guaranteed return to a higher guaranteed return, and update the database to store the closing price as of the current date as the high-watermark value; re-price a notional amount of at least one guarantee contract in view of changes in the ANAV relative to the ANAV on a prior date, wherein each said guarantee contract is separate from and in addition to said traditional assets of the fund and collectively support the guaranteed return and any higher guaranteed return; price the fund at the close of the current date by adding each re-priced guarantee contract to the ANAV while the traditional assets remain fully and permanently invested in the market; and publish the price for use on the current date.