A Farm Economy Coefficient Generator (FECG) is presented as a post-processing tool for agro-ecological simulation models (ASMs) that deliver yields and consumption figures for nitrogen fertiliser and irrigation water use. The FECG carries out simple cost accountancy calculations using typical production techniques, costs and prices for the selected area. The default settings can be adjusted by the user to specifically describe local farm management. Together with various ASMs, the FECG is embedded in a web-based, geo-referenced decision support system to enable users to extract information on future yields and net returns on a regional or farm-level basis. Using the example of a winter wheat-winter barley-silage maize crop rotation in Germany and downscaled A1B climate data it was demonstrated how the ASM-FECG tandem can be used to analyse the cost and benefit of irrigation. In this example the irrigation costs would still outweigh the yield increase today, while in around 2070 the increased difference between potential and water-limited yield is likely to make irrigation profitable, provided that costs and price levels remain constant. The susceptibility of these results to changing market conditions is discussed. (C) 2013 Elsevier B.V. All rights reserved.