ENThe article is based on Jan Karol Chodkiewicz's debt registers, supplemented by the information drawn, among other things, from correspondence and estate inventories. The example of the Grand Hetman of Lithuania’s activity serves as a pre text to pose questions about the profitability of military service in the first half of the seventeenth century, the amount and structure of magnates' income and the place of credit in the economy of the great landowners of the Commonwealth. Keywords: Grand Duchy of Lithuania, magnates, Jan Karol Chodkiewicz, finance, debt. [From the publication]