How is the Zakat for a lamb meat shop calculated: Is it on the full income or on the money remaining after expenses, and is Zakat obligatory on livestock that is purchased in installments, even if their total number exceeds the nisab within the year?

The husband must pay Zakat (definition) on trade goods if a hawl (full lunar year) has passed since the initial capital was invested in his trade and it reached the nisab (definition) (minimum threshold). Livestock and meat present on the Zakat due date are to be valued at market price. Remaining cash and hopeful debts are to be added to this value. Then, one-quarter of one-tenth (2.5%) of the total is to be paid. Whatever was spent or consumed during the year is not subject to Zakat; only what is present on the Zakat due date is to be valued. Land, ponds, and machinery prepared for use are not subject to Zakat.