It is permissible to provide fidya (compensation) for elderly individuals or those suffering from severe illnesses who, due to their health condition, do not have hope of being able to fast during Ramadan. The fidya for each missed fast is equivalent to the amount given as Sadaqat al-Fitr. It is better to pay the fidya during the blessed month of Ramadan, but if not paid during Ramadan, it can be given later. A person who is hopeful of recovering from an illness should not pay fidya. Instead, they should make up for the missed fasts during Ramadan that were left due to illness after recovering.
Every mentally sound, adult, and healthy Muslim is obligated to observe fasting. Fulfilling someone else’s missed fasts does not fulfill one’s own obligation to fast.