Adding nitrogen fertiliser initially increases yield, but as the crop nears optimal N levels, yield gains plateau. Beyond this, extra N costs may not be recovered by additional grain value—this defines the Break-Even Ratio (BER). Growers should use current fertiliser and grain prices to estimate the N rate where fertiliser cost equals extra grain value. BER assumes a highly accurate base recommendation, so in normal years with stable prices (BER ~6-9), detailed BER analysis may only be a rough guide, especially when fertiliser prices are high compared to grain prices. Example: Calcium ammonium nitrate costs €450/t (~€1.66/kg N). Grain price is €150/t (€0.15/kg). At the yield plateau’s low end, 1 kg N produces 30 kg grain (€4.50), covering fertiliser cost (€1.66). At higher N rates, 1 kg N produces only 11 kg grain (€1.65), barely covering cost, so extra N is uneconomical.