Pasture-cropping is a novel approach to increasing the area of perennial forages in mixed livestock and cropping systems. It involves planting annual cereals directly into a living perennial pasture. There is interest in using subtropical grasses for pasture-cropping as they are winter dormant and their growth profile is complementary with winter crops. The ability of subtropical grasses to maintain feed quality in summer is likely to be an important attribute. However, a wide range of factors can affect the uptake of such systems. This paper evaluates the farm-system economics of subtropical grasses and pasture-cropping. The research question is: what factors affect the profitability of a new technology such as (1) subtropical grass and (2) subtropical grass that is pasture-cropped. The analysis uses the MIDAS model of a central wheatbelt farm in Western Australia. The results suggest the profitability and adoption of subtropical grasses is likely to be strongly influenced by the mix of soil types present on the farm; the feed quality of the subtropical grass; whether the production emphasis of the farm is for grazing or cropping, and the level of production in summer and early autumn. The same factors are relevant to pasture-cropping, with the addition of yield penalties due to competition between the arable crop and the host perennial. The results were less sensitive to changes in the winter production of subtropical grass. Pasture-cropping was more profitable and likely to involve a larger area of the farm when a meat rather than a wool-dominant sheep system was present. However, there was little difference between the meat and wool flocks in their sensitivity to other factors in this analysis.