When is Zakat due on saved money from which one spends, and what is the amount upon which it is calculated?

It is permissible for a Muslim to pay zakat on their wealth and savings from salaries according to two opinions. One opinion, which is more cautious, more convenient for you, and more beneficial for the needy, is that you identify the day your wealth reached the nisab (minimum threshold), and on the same day in the following year, you pay zakat on all the wealth you possess. The second opinion is that you pay zakat on the wealth that has reached the nisab at the end of its hawl (one lunar year), and then you pay zakat on each amount you save from your salary when its own specific hawl is completed. The first opinion is more convenient and more beneficial for the poor, and it involves hastening the zakat on some wealth before its hawl is completed, which is permissible.