Abstract Nitrogen (N) budgets were determined for six typical, moderately intensive dairy farms in south-west England. Proportionately, only 0·12–0·17 of the N input to the farms was recovered in agricultural products, leaving annual N surpluses equivalent to 249–376 kg N ha−1. A sequence of models (MANNER, NCYCLE and SUNDIAL) was used, together with the estimated N balance of the dairy cows and standard ammonia emission factors, to estimate N losses for each farm. Total estimated losses were equivalent to 137–220 kg N ha−1 year−1. Leaching accounted for 0·26–0·45 of the total loss, ammonia volatilization for 0·27–0·39 and denitrification for 0·17–0·36. When residual N from manure applications was included, there appeared to be an annual accumulation of soil N, equivalent to 66–158 kg N ha−1 when averaged over the whole farm area. The amounts of N lost by leaching, volatilization and denitrification, and accumulated as soil-N, were determined by a combination of farm properties, including N input, soil type, drainage, characteristics of the manure produced and type of fertilizer. The sum of estimated losses and change in N retained on the farm was between 0·85 and 1·11 of the N surplus (input minus output) determined from the farm budget. This suggests that losses and the change in soil-N were underestimated on some farms and overestimated on others (by up to −50 and +23 kg N ha−1 respectively). Much of the discrepancy between estimates and the surplus was attributed to difficulties of fully integrating inputs and outputs between the different models and stages of the modelling procedure.