One of the economic responsibilities of the Muslims is to pay the Khums; which means that on certain items, 1/5 or 20% (of the value of that item) must be paid to a Mujtahid, which will be used for specific purposes.
2. Just like Salat and Fasting, the paying of Khums is one of the Wajibat, and anyone who possesses one of the seven things listed above, must act according to that which will follow (in relation to the paying of Khums).
One of the instances of Khums that include most people in the society is giving Khums on that which exceeds a person and his families’ yearly expenses (benefit/profit from working). Islam respects a person working and earning, and thus places preference over securing one’s needs over that of paying the Khums. Therefore, one who can secure his (financial) needs from his earnings, if after securing his (financial) needs nothing remains at the end of the year, then Khums will not be obligatory on him.
But, if after calculating all the normal expenses for his life (and the maintenance of his family) according to his (social) status and needs, and without being extravagant or miserly, if something remains at the end of the year, then 1/5 (or 20%) of that which remains must go towards the specified expense (of Khums), and 4/5 (80%) of the amount that is left can be put into one’s savings.
 The Christians, Jews and Zoroastrians that have made a contract with the Islamic ruler that they will pay a certain amount of money in tax, and that they will accept the specific conditions (that are listed in the detailed books of fiqh), are referred to as Kafir Dhimmi, and their lives and properties are protected (in exchange for paying the tax and accepting the conditions).