Kupnina [kupˈnina] is a village in the administrative district of Gmina Nowogród, within Łomża County, Podlaskie Voivodeship, in north-eastern Poland. It lies approximately 8 kilometres (5 mi) north-east of Nowogród, 16 km (10 mi) north-west of Łomża, and 84 km (52 mi) west of the regional capital Białystok.