This type of Zakat should be set aside on the eve of Eid al-Fitr and be paid on the day itself, which marks the first day of the month of Shawwal.
What fallows is the Fatwas of Grand Ayatollah Sistani regarding the Fiṭrah Alms Tax (Zakāt al-Fiṭrah):
Ruling 1. A person who at the time of sunset (ghurūb) on the eve of Eid al-Fiṭr is bāligh and sane, and not unconscious, poor, or a slave, must give on his behalf and on behalf of those who are dependent on him, one ṣāʿ – which is approximately three kilograms – of food per head to someone who is entitled to receive zakat. The food that he gives must be considered to be a staple food in his town, such as wheat, barley, dates, raisins, rice, millet, or something similar, and it suffices if he gives the food’s monetary value instead. The obligatory precaution is that food that is not considered to be staple in his town must not be given as zakat even if what he gives is wheat, barley, dates, or raisins.
Ruling 2. If a person cannot meet his and his family’s living expenses for one year and does not have an occupation by which he can meet his and his family’s expenses for one year, then such a person is a poor person and it is not obligatory on him to give zakāt al-fiṭrah.
Ruling 3. A person must give fiṭrah on behalf of all those who are considered to be his dependents at the time of sunset on the eve of Eid al-Fiṭr, irrespective of whether they are young or old, Muslims or disbelievers, and whether it is obligatory on him to pay for their living expenses or not, and whether they are in his town or in another town.
Ruling 4. If a person appoints his dependant who is in another town to be his agent and give the dependant’s fiṭrah from that person’s property, in the event that he is confident that he will give the fiṭrah, it is not necessary for the person to give his dependent’s fiṭrah himself.
Ruling 5. It is obligatory on one to give the fiṭrah of a guest who arrives at his house before sunset on the eve of Eid al-Fiṭr and spends the night at his place and is considered to be his dependent, albeit only temporarily.
Ruling 6. The fiṭrah of a guest who arrives at one’s house after sunset on the eve of Eid al-Fiṭr is, based on precaution, obligatory on the host provided that the guest is considered to be the host’s dependent; otherwise, it is not. If a person is invited to break his fast (ifṭār) on the eve of Eid al-Fiṭr, he is not considered to be the host’s dependent and the guest’s fiṭrah is not the responsibility of the owner of the house.
Ruling 7. If a person is insane at the time of sunset on the eve of Eid al-Fiṭr and his insanity continues until the time for ẓuhr prayers on the day Eid al-Fiṭr, zakāt al-fiṭrah is not obligatory on him; otherwise, based on obligatory precaution, it is necessary for him to give fiṭrah.
Ruling 8. If before sunset a child becomes bāligh, or an insane person becomes sane, or a poor person becomes rich, and if that person meets the conditions that make it obligatory on one to give fiṭrah, he must give fiṭrah.
Ruling 9. If at the time of sunset on the eve of Eid al-Fiṭr a person does not meet the conditions that make it obligatory on him to give fiṭrah but before the time for ẓuhr prayers on the day of Eid he does meet the conditions, then the obligatory precaution is that he must give fiṭrah.
Ruling 10. If a disbeliever becomes Muslim after sunset on the eve of Eid al-Fiṭr, it is not obligatory on him to give zakāt al-fiṭrah. However, if a Muslim who was not a Shia becomes a Shia after the moon is sighted, he must give fiṭrah.
Ruling 11. If someone possesses only one ṣāʿ of wheat and suchlike, it is recommended that he gives zakāt al-fiṭrah. In the event that he has dependents and he wants to give their fiṭrah as well, he can give that one ṣāʿ to one of them with the intention of giving fiṭrah, and the recipient can in turn give it to another dependent with the same intention, and so on until it reaches the last person; and it is better that the last recipient gives the item to someone who is not a member of their family. If one of them is a minor (ṣaghīr) or insane, his guardian can take it on his behalf; and the recommended precaution is that the guardian should not take it with the intention of taking it for the minor or insane person but rather for himself.
Ruling 12. If after sunset on the eve of Eid al-Fiṭr a woman gives birth to a child, it is not obligatory to give fiṭrah for the child. However, if before sunset a woman gives birth or marries and the mother or wife are considered to be dependents of the father or husband, then he must give their fiṭrah; but if they are dependents of someone else, then it is not obligatory on him. And if they are not dependents of anyone, then the fiṭrah of the woman is obligatory on herself and there is no obligation to give fiṭrah for the child.
Ruling 13. If a person is a dependent of someone and before sunset he becomes a dependent of someone else, his fiṭrah is obligatory on the person of whom he became a dependent. For example, if a girl moves to her husband’s house before sunset, her husband must give her fiṭrah.
Ruling 14. A person whose fiṭrah is obligatory on another person is not obligated to give his fiṭrah himself. However, if the other person does not or cannot give his fiṭrah, then based on precaution it becomes obligatory on him to give his own fiṭrah provided that the conditions mentioned in Ruling 2003 are fulfilled.
Ruling 15. If a person whose fiṭrah is obligatory on another person gives his own fiṭrah, the obligation on the one who must give it is not exempted.
Ruling 16. A person who is not a sayyid cannot give fiṭrah to a sayyid, and even if that sayyid is his dependent, he cannot give that sayyid’s fiṭrah to another sayyid.
Ruling 17. The fiṭrah of a child who is breastfed by its mother or a wet nurse is obligatory on the person who pays for the living expenses of the mother or the wet nurse. However, if the mother or the wet nurse takes her living expenses from the child’s property, then the fiṭrah of that child is not obligatory on anyone.
Ruling 18. Even if a person pays for the living expenses of his dependents with property that he has acquired unlawfully, he must give their fiṭrah from property that he has acquired lawfully.
Ruling 19. If a person hires someone like a builder, carpenter, or a servant, and pays for his living expenses in a manner that the hired person is considered to be his dependent, he must give the hired person’s fiṭrah as well. However, if he only pays him for his work, then it is not obligatory on him to give his fiṭrah.
Ruling 20. If a person dies before sunset on the eve of Eid al-Fiṭr, it is not obligatory to give his and his dependents’ fiṭrah from his estate. However, if a person dies after sunset, then based on the well-known (mashhūr) juristic opinion, his and his dependents’ fiṭrah must be given from his estate. However, this rule is problematic, and the requisite precautionary action must not be abandoned.