This spreadsheet is a model of the economics of deficit irrigation that is described in detail in: Trout, T.J. and D.T. Manning. 2019. An economic and biophysical model of deficit irrigation. Agron. J. 111:1–12. doi:10.2134/agronj2019.03.0209 . The model calculates net income from a crop on a unit of land based on a quadratic crop water production function, amount of effective precipitation, irrigation efficiency, cost of the irrigation water supply, crop production costs, and revenue from selling the crop. The model includes potential income from leasing out saved irrigation water. All biophysical variables are defined in terms of the relative evapotranspiration. Net income is maximized by optimizing the amount of water consumed by the crop. The spreadsheet progressively presents biophysical and economic models of deficit irrigation with water leasing. Economic and biophysical parameters are input into the highlighted cells of each worksheet. Parameters from previous worksheets are copied to following worksheets. Relationships are graphed. Output is the net income (NI) for a set of biophysical and economic parameters and level of deficit irrigation that maximizes net income.