What should we do regarding paying Zakat for past years on behalf of my husband, who has not paid it since 2009, and how do we calculate it, especially given his inability to recall the amounts and the dates they reached the nisab? Is it permissible to pay it in installments, and is Zakat due on the principal amount or on the total amount including interest?

Firstly: The nisab (minimum taxable amount) for paper currency is estimated by the lesser of the two nisabs of silver and gold, which is 85 grams of gold or 595 grams of silver. Zakat becomes obligatory for anyone who possesses this nisab, even if the money is saved for future needs.

Secondly: If the money is placed in an interest-bearing (usurious) bank, Zakat is due only on the principal amount, not on the interest, because the interest is forbidden (haram) and must be disposed of.

Thirdly: Zakat does not lapse with the passage of time. Whoever neglected to pay it for years must pay it for all past years, along with repenting for this delay.

Fourthly: The husband must estimate the amount of money he possessed in each year to pay Zakat. If he is uncertain, he should act cautiously. He can consult the bank to obtain an account statement after deducting the usurious interest.

Fifthly: Zakat must be paid immediately, and its delay is not permissible except for a valid excuse, such as lack of liquidity.

Sixthly: Repentance to Allah Almighty is obligatory for not having paid Zakat in the past period.