Dr. Muzammil Siddiqi, former president of the Islamic Society of North America (ISNA), states: It is permissible to pay the Zakah in advance. It is reported by Imam At-Tirmidhi as well as Abu Dawud, Ibn Majah and Ad-Darmi that ‘Ali, may Allah be pleased with him, asked the Prophet, peace and blessings be upon him, about this and he gave him permission to pay the Zakah in advance.

However, before giving the Zakah in advance one must make a Niyah or intention that it is the following year’s Zakah. The intention is necessary otherwise it will be a charity or Sadaqah and one has to give the Zakah on its time again. The Zakah still has to be calculated at the end of the year.
If the amount paid is less than what is owed, then the balance must be paid to fulfill the obligation. If the amount paid is more than what is owed, then one cannot take it back from the poor people It will become the Sadaqah and Insha’ Allah one will receive the reward for it.

In addition, it is also allowed to give the Zakah in installments, provided it is given in advance. Suppose one calculated that at the end of this year that he/she would have to give $1200 dollars in Zakah. One can give this amount on a monthly or quarterly basis before the end of the Zakah year. If a person dies before paying off his/her Zakah dues, his/her heirs should pay the remaining balance from his/her wealth, before the distribution of the inheritance.