The calculator estimates the nutrient balance for each field based on crop requirements and planned fertilization. Based on the differences, the farmer may then increase or decrease his manure or fertiliser inputs to obtain a better match.

The calculator estimates the amounts of nitrogen (N), phosphate (P205) and potash (K2O) required by crops as recommended by DEFRA Fertilizer Recommendations for Agricultural and Horticultural Crops (RB209) and outlined in the Northern Ireland Nitrates Action Programme (NINAP). It helps farmers match the nutrient requirements of a crop to that supplied by organic manures and chemical fertilizer. It also helps them comply with nutrient limit requirements for the NINAP and supplies and compiles essential information required for record keeping. To ensure that the NINAP nitrogen limit is not exceeded for the whole grassland area, the farmer is also advised to use the N Max for Grassland Calculator [UK05].