The adverse effect of increasing age and/or body weight on distance run performance has been well documented. Accordingly, nearly all five kilometer (5K) road races employ age categories and, sometimes, a heavier body weight classification. Problems with such conventions include small numbers of runners within older age categories and the advantage given to the lightest runners within each weight category. We developed a 5K Handicap (5KH), a model that calculates an adjusted run time based on the inputs of actual 5K run time, age, and body weight for men and women. This adjusted time, then, can be compared between runners of different ages and body weights. The purpose of this paper was to explain, in detail, the derivation of the 5KH formula using published theoretical and empirical findings on age, body weight and distance run time relationships. To our knowledge, the 5KH is the first such model and overcomes the problems associated with being heavier within one weight class and having too few runners in certain age categories. We are currently undertaking large-scale validation studies and evaluation of its race day implementation.