How is Zakat accurately calculated for previous years when some money has been spent, and is Zakat due on money six times, and what about the spent money whose exact amount is unknown?

Zakat is one of the pillars of Islam, and it must be paid as required. Money consumed before the completion of the hawl (one lunar year), the price of a residential or rental car, and the price of a dwelling are not included in the nisab (the minimum amount of wealth subject to zakat). You must review your accounts for the past six years and pay zakat on the money that has completed its hawl, without counting consumptions, or the price of a car, or a dwelling. The amount of zakat is two and a half percent. After calculating the due amount, the two thousand that were already given out should be deducted, and the remainder should then be paid. If the matter is unclear, one must strive and investigate, and err on the side of caution by giving out more to absolve one's responsibility.