Models that estimate P-loss from agricultural land to surface waters are important tools used by soil scientists, catchment scientists and land managers, to help identify high-risk areas and determine measures which can reduce such losses. A widely used method for predicting P-loss from agricultural land is the ‘Phosphorus Index’ (PI) tool, developed by Lemunyon & Gilbert (1993), which requires relatively basic input data, and provides a qualitative estimate of the risk of P-loss from agricultural fields. The PI delivers a single numerical score, typically expressed as a risk factor ranging from ‘low’ to ‘very high’. Across the USA, state-wide adaptations to the original PI resulted in widely differing indices. In an attempt to reduce these inter-state discrepancies, the US Department for Agriculture developed the Annual Phosphorus Loss Estimator (APLE; Vadas et al., 2009) tool in order to provide a more transparent and quantitative (rather than qualitative) output for both particulate and dissolved P-fractions. This short review compares the latest incarnation of the PI in the APLE tool with other P management indices and explores the various features and opportunities included in the model’s inbuilt equations.