Planning for the maintenance and sustainability of legacy systems often involves attempting to time the obsolescence of a component or a system of components. Serious questions arise, such as: When will critical parts no longer be available? Will the next-generation technology replacing the current technology have a serious impact on system maintenance, repair, operation, or performance? When will software systems no longer be supported? These questions, if not outright overlooked, are often answered using qualitative information, such as expert opinions, market forecasts, or supplier assurances. However, reliable quantitative methods have been developed that project the growth and diffusion of technology in time, including projecting technology substitutions, saturation levels, and performance improvements. These quantitative technology forecasts can be applied at the early, mid-life, and even end-life stages of Navy technology platforms to better plan legacy system maintenance and sustainability strategies. In practice, a quantitative technology forecast is completed to ascertain the time in the future when a technology trajectory would have a significant impact on the sustainability of a legacy technology, system, or platform. Such future projections provide reliable time-referenced information when considering cost and resource requirement trade-off strategies to maintain or replace a component or system. This paper introduces various quantitative technology forecasting techniques and illustrates their practical applications toward considering legacy system support strategies.