This background note describes the methodology of the AMIS fertilizer cost index featured in the Fertilizer Section of the AMIS Market Monitor since September 2024. The index aims to monitor the evolution of fertilizer costs per hectare depending on the crop, in selected leading crop producing countries. For each country-crop combination, fertilizer costs are obtained by linking selected fertilizer prices at either import or retail level (depending on data availability), with corresponding country-specific application rates by nutrient.