Is Zakat obligatory on a sum of money that has been in a bank account for a year, knowing that the amount increased and decreased during the year?

Zakat is obligatory on borrowed money under two conditions: that the money reaches the nisab either by itself or by being combined with other money or trade goods one owns, and that a full lunar year passes over it. The nisab is equivalent to 85 grams of gold or 595 grams of silver. If the money reaches the nisab and a full year passes over it without falling below the nisab, then a quarter of a tenth (2.5%) of it must be given as zakat. However, if it does not reach the nisab or falls below it before the end of the year, then zakat is not obligatory on it. Increases and decreases in the loan amount affect the obligation of zakat if they lead to the amount falling below the nisab during the year. It must be known that borrowing with riba (usury/interest) is one of the grave major sins.