How is Zakat on money calculated for a bank balance designated for debt repayment, and is Zakat obligatory on debts owed to you by people that are repaid in monthly installments?

Zakat (definition) becomes obligatory if the wealth reaches the nisab (definition) and a full year (hawl) has passed over it, provided there is other wealth sufficient to cover any debt. However, if the debt consumes the wealth entirely or reduces it below the nisab, then Zakat is not obligatory. As for a debt owed by someone who denies it or procrastinates, Zakat is not obligatory on it until it is received, at which point it is paid for one year. But for a debt owed by an affluent person who acknowledges it, Zakat is paid when a full year has passed over it.