The reference nutrient intake, abbreviated RNI, is the amount of a nutrient judged sufficient for the needs of nearly all healthy people in a population group. It belongs to the family of dietary reference values used in the United Kingdom: set at two standard deviations above the estimated average requirement, it covers about 97.5% of the group. Dietitians use RNIs to plan diets, assess intakes, and set food labelling reference values, though an individual’s true requirement may be lower. Intakes consistently below the lower reference nutrient intake signal likely deficiency. The RNI is a planning and assessment tool, not a personal target to chase daily, and it applies to healthy populations rather than to people with disease or exceptional needs.