I can not fast for medical reason. Can I calculate the cost of feeding a poor person and give it to him at once?
All perfect praise be to Allaah, The Lord of the Worlds. I testify that there is none worthy of worship except Allaah, and that Muhammad is His slave and Messenger. We ask Allaah to exalt his mention as well as that of his family and all his companions.
If a person has a chronic disease due to which he is unable to fast, then he may break the fast and feed one poor person for every day he missed. Feeding a poor person is estimated at 750 grams of food. The most preponderant opinion of Muslim scholars, may Allaah have mercy upon them, is that giving cash money instead of feeding is not sufficient. It is also not accepted from him to feed the same person all the days he missed, but he is obliged to feed a different poor person for every day he missed according to Imaam Maalik, may Allaah have mercy upon him.
However, the Hanbali school are of the view that it is permissible to feed the same person for all the days one missed, either by giving him the total amount at once or feeding him every day. Of course, it is valid to feed a poor person only after one's breaking the fast [i.e. it is not acceptable from him to feed a person in advance, that is to say before the day one breaks the fast].
Allaah Knows best.
Fatwa answered by: The Fatwa Center at Islamweb