Is zakat obligatory on a monthly salary from past years, given the existence of successive debts and loans, and the lack of sufficient savings to cover the installments?

If the saved salary reaches the nisab (85 grams of gold or 595 grams of silver) after deducting debts, and a full lunar year (hawl) has passed over it, then zakat of 2.5% becomes obligatory on it. It must be paid immediately if it was not paid on time, and it does not lapse with the passage of time. However, if the saved salary does not reach the nisab after deducting debts, then no zakat is due on it.