All perfect praise be to Allah, The Lord of the Worlds. I testify that there is none worthy of worship except Allah, and that Muhammad is His slave and Messenger.
Allah Almighty has permitted a sick person who hopes for a cure from his sickness to break his fast during the month of Ramadan, but he has to make up the number of days he missed later.
Allah Says (what means): {…So whoever among you is ill or on a journey [during them] - then an equal number of days [are to be made up].} [Quran 2:184]
The aforementioned ruling applies to the sick person whose illness is temporary. The chronically ill person who has no hope of cure, and faces much hardship in fasting, must pay expiation for the missed fast. The expiation is to feed a poor person for every day he missed.
Therefore, the view we adopt here in Islamweb is that if the doctors certify that your illness will continue and there is no hope of cure and you face much difficulty in fasting, then you have to give expiation; i.e. feeding a poor person for every day you miss to fast.
If the illness is curable, then you should wait till you are cured and then make up the missed days. Making up the missed days could be after the next Ramadan since this delaying is due to a legal excuse; thus, you are not sinful and you are not obliged to pay any expiation.
Allah knows best.