All perfect praise be to Allah, The Lord of The Worlds; and may His blessings and peace be upon our Prophet Mohammad and upon all his family and companions.
An old person who is unable to fast is obligated to pay the Fidyah-the one who is unable to fast for the rest of his life-, which is feeding a needy Muslim for each missed day a Mud (600 grams) of food; wheat or rice. The monetary value of a Mud is estimated these days at one Dinar, as determined by the Jordan Iftaa` Council. Allah, The Almighty, says in this regard (What means): “ For those who can do it (With hardship), is a ransom, the feeding of one that is indigent. “ {Al-Baqarah/184}.
As regards the manner of paying this Fidyah, advancing or deferring it, Muslim jurists have two opinions:
The first opinion:
It is permissible for the old and the ill who is inflicted with an incurable disease to pay the Fidyah for the whole month of Ramadan at its beginning.
It is also permissible to delay it until the end of Ramadan according to the Hanafite school of jurisprudence.
It was stated in the books [Ad`dur al Mokhtar and Hashiat Ibn Abdeen] (2/427): “ An old person who is unable to fast is permitted to break his fast, but he must pay the Fidyah, even at the beginning of the month. In other words, he is free to pay it at the beginning, or at end of Ramadan.”
The second opinion: The Shafite jurists are of the view that the Fidyah must be paid day by day after breaking the fast of each day, or for the day on which the fast was broken after crack of dawn or before that and to be paid at night, or to be paid once Ramadan ends. Even if they paid the Fidyah of the whole days of the month in advance, it remains a debt on them. It is stated in [Moghni al-Mohtajj]. The old, the ill, the pregnant, and the suckling aren`t permitted to pay the Fidyah of two days, or more in advance. Moreover, it isn`t permissible to pay the Zakat (alms) of two years in advance. An-Nawawi (May Allah have mercy on his soul) stated in his book [Al-Majmou` (6/260)]: “ Our fellow scholars have agreed that it isn`t permissible for the old and the ill who suffers from an incurable disease to pay the Fidyah in advance before the start of Ramadan. However, it is permissible to pay it after the rise of the dawn of each fasting day. Is it permissible to pay it before dawn? Ad-Darimi said: It is conclusively permissible and this is the correct opinion. “
In brief, there is no harm in giving the Fidyah of the whole month in advance in accordance with the Hanafite school of jurisprudence. However, it is better to avoid the difference of opinion among the scholars (to be on the safe side) by giving it for each day after breaking the fast of that day, or at the end of Ramadan. And Allah knows best.