What is the amount of zakat that must be paid, and when is it due, given the existence of cash balances, gold, silver, merchandise, debts owed by others, debts owed to others, commercial shop rent, housing rent, and other expenses?

Zakat (definition) is calculated at the end of each Hijri year, starting from the date the nisab (definition) (minimum threshold) was attained. This involves accumulating liquid assets, debts that are expected to be repaid, and trade goods (at their market value). Then, any outstanding debts you owe are deducted. One-quarter of one-tenth (2.5%) of the remainder is then paid as Zakat. As for unrecoverable debts, they are not subject to Zakat unless they are collected, in which case Zakat is paid for one year. One must avoid dealing with usurious banks.