I'm retired. Must pay monthly 600 dollars for my 2 sons schooling for the next 3 years. The amount of money I have in bank can hardly cover above expenses. Should Zakaat apply?

All perfect praise be to Allaah, The Lord of the Worlds. I testify that there is none worthy of worship except Allaah, and that Muhammad is His slave and Messenger. We ask Allaah to exalt his mention as well as that of his family and all his companions.

Any Muslim who totally possesses an amount of money that reaches the minimum amount liable for Zakat and a whole lunar year elapses on it, he has to pay Zakat on it. Allaah says (which means): {Take, [O Muhammad ], from their wealth a charity by which you purify them and cause them increase, and invoke [Allaah’s blessings] upon them. Indeed, your invocations are reassurance for them. And Allaah is All-Hearing and All-Knowing.}[Quran 9:103].

Moreover, when the Prophet sent Mu’aath to Yemen he told him: "Inform them that Allaah imposed on them Zakat (alms) which should be taken from the rich of their people and be given to the poor." [Al-Bukhari and Muslim]

Therefore, you have to pay Zakat on the money that is in your possession if it reaches the minimum amount liable for Zakat and a whole lunar year elapses on it, whether you saved this money to spend on you, on the members of your family [on whom you are obliged to spend],  on their studies, or otherwise.

You have to know, dear brother, that paying the Zakat is a sign of fearing Allaah and Allaah promised he who fears him to make a way out to his difficulty and hardship. Allaah says (which means): {… And whosoever fears Allaah and keeps his duty to Him, He will make a way for him to get out (from every difficulty). And He will provide him from (sources) he never could imagine.}[Quran 65:2-3]. Spending out of one's wealth [money] is also a way of increasing it and getting the Blessings of Allaah on it. Allaah says (which means): {…and nothing do you spend in the least (in His Cause) but He replaces it: for He is the Best of those who grant Sustenance.}[Qur'an 34:39]. Besides, the Prophet said: "Spending in charity never decreases wealth, and Allaah does not increase the one who pardons except by more honour, and Allaah raises the status of the person who humbles himself for Allaah's Sake." [Muslim]  In another narration the Prophet said: "Spending in charity does not decrease wealth." [At-Tabaraani]

As regards the ruling of saving money in banks which deal with usury and interest, please refer to Fatawa: 86014 

Allaah knows best.