Is Zakat obligatory upon the debtor or the creditor if a year has passed over a sum of money owned by the debtor, while he owes a debt to another?

If the money you possess does not exceed your debt, then according to the majority of scholars, no zakat is due upon you. However, if you have additional funds that exceed your basic needs, which are not subject to zakat, then consider them in lieu of the debt and pay zakat on the amount if a full year has passed while it reached the nisab. The value of the nisab is estimated at 85 grams of gold, and the amount due is one-quarter of one-tenth (2.5%). As for zakat on the debt owed by your brother: if the debtor is solvent and not procrastinating, then zakat is due on it. But if he is insolvent or procrastinating, then no zakat is due until its owner receives it, whereupon he pays zakat for one year.