There are a good number of IR sensor models available to the electro-optical community. These models predict sensor performance in terms of the system's probability to perform discriminating tasks as a function of target range and geometry, system minimum resolvable temperature and meteorological conditions. However, these models are tedious to use, and require intimate data pertaining to sensor output signal processing and display. Furthermore, these models lack the flexibility in, for example, displaying intermediate results in modifying probability statistics. Although these models are proven analytical tools, their use is somewhat prohibitive when performing every day desk-top calculations. This paper shows how general mathematics software packages available for personal computers, such as MathCad and Mathematica, can be used for rapid and reasonably accurate performance modelling of IR sensors. Examples discussed are estimating apparent target temperature difference, performance modelling using MRT data and transmission modelling.