Tail biting is a behavioural problem with both welfare and economic consequences. Various conditions that may contribute to tail biting have been identified in a number of research reports. This paper examined those reports and extracted these causative factors. A weighting factor was developed for each of these contributing conditions, and a model developed to estimate the risk of tail biting in any housing/management system. The contributing factors, ranked from those most to least likely to affect tail biting were: tail docking, diet, substrate, weaning environment, sex, weight or age, food related agonism, growth retardation, worms, space per pig, trichinosis, heat, season, floor type, ventilation type, feed moisture, feeding synchrony, group size, feeding automation, time of day, tail injury, coldness, water provision, breed, herd size, light, air quality and group stability. The model can be upgraded as new information becomes available.