This article presents a comparison of nitrogen balances obtained on the basis of different methodologies applied in Poland and other countries to estimate N loss potential from agricultural sources. In the study, data from 130 agricultural farms situated in four regions, Wielkopolska, Lubuskie, Dolny Śląsk, and Opole, were used. Some of the analyzed farms were situated in nitrate vulnerable zones (NVZs). Seven types of ‘field surface’ and four types of ‘farmgate’ balances were selected. The comparison of the selected balances revealed considerable discrepancies in the results reaching 50 kg N·ha^-1 in the case of field surface balances. With regard to ‘farmgate’ balances, differences in individual groups of farms sometimes exceeded 50 kg N·ha^-1.