Dr. Monzer Kahf, a prominent economist and counselor states: “Let us assume that a salary earner has already established a Zakah year for them-self. (It is a lunar year [= 354 days] that begins on the day one gets a Nisab [= approximately US$ 1000] for the first time). Now at the end of each such a year, one is to look at the balance they have on all their checking and saving accounts + other funds and investments + the balance in the pension plan + debts they have on other persons – short term debts on you [e.g. one does not deduct a home long term debt] and they’re to multiply the total by 2.5%. This is the amount of Zakah. It means:
we took end of year balance; all withdrawals have already gone, no Zakah on them; all additions during the year are included although on none of them a year have passed, and it does not matter what is the source of these additions, savings, gains or gifts and contributions from others.