Is zakat obligatory on money deposited in a bank and designated for furnishing the marital apartment, or on the incomplete installment of the apartment? And how is zakat calculated in this case?

The Hijri date must be used for calculating zakat (definition) from the day of possessing the nisab (definition) (85 grams of gold or 595 grams of silver). Zakat is obligatory on wealth prepared for essential needs, such as an apartment and furniture. It is permissible to deduct the apartment installment from the principal amount. If, after deduction, what remains reaches the nisab and a full year has passed over it, zakat becomes obligatory on it at 2.5%. However, if there is non-zakat-eligible wealth that exceeds one's needs (like a car), it can be used to cover the installment, and in this case, the installment is not deducted from the principal amount.