Farm management occurs against a backdrop of weather-year variation. In Australian mixed enterprise farming systems, how important is it for farm optimisation models to capture this variation and the management tactics matched to that variation? This study compares two whole farm optimisation models of an Australian mixed enterprise farming system. One model represents weather-year variation and the short-term tactical management responses tailored to the unfolding weather-year conditions. The other model is a traditional deterministic steady state model that employs the key assumption that every year is an expected weather-year. Both models require the farm manager to select a profit-maximising suite of enterprises and activities relevant to either the expected weather-year or the suite of weather-years that typify weather-year variation where the farm is located. Comparison of the models’ results reveals key differences in farm strategy, farm tactics and farm profit. The model that includes tactics aligned to the weather-year variation reveals that tactical decision-making increases expected farm profit by about 18 per cent.