How do I pay zakat on my money for the past six years, which has not had a full year pass on it because it is profit from an establishment that is constantly entering and exiting?

Zakat is obligatory upon anyone who possesses the nisab (the equivalent of 85 grams of pure gold) and a full lunar year has passed since acquiring it. The amount of Zakat that must be given is 2.5% of the wealth. For anyone who has not paid the obligatory Zakat, it remains a debt upon them that must be paid, no matter how many years have passed. If you spend the money before a full year has passed, then no Zakat is due on it. However, if you possessed the nisab and a full year passed, and you did not pay Zakat in previous years, then you must repent to Allah and immediately pay the Zakat for all those years, estimating the amount if you do not know it precisely. Sheikh Al-Uthaymeen said: "It is obligatory to pay Zakat immediately upon its due date. Whoever delays it must repent and promptly pay it for all that has passed."