This document provides instructions for rolling over a welcome free bet by laying a bet at Betfair to offset the risk of the free bet placed at a sportsbook. It recommends finding the highest odds possible, such as 4.5 or above, to maximize profits. An example is shown where odds of 13.0 are found at Skybet for a horse, while odds of 11.5 are available to lay the same horse at Betfair, resulting in a 99% profit guarantee from the £20 free bet. The calculator helps determine the amount to lay at Betfair to balance the risk from the sportsbook free bet.