All praise is due to Allah, peace and blessing be upon Prophet Mohammad.

One who broke fast in Ramadan for a lawful excuse and was capable of fasting after that excuse had ended is obliged to make up for the missed fast.

However, if they were entirely incapable of fasting due to old age, or an incurable disease, then they must pay a ransom which is feeding a needy Muslim person a Mudd(600gr.) from the common food of the country for each missed day. Also, it is permissible to give the value of the Mudd which varies according to time and place, and in Jordan, it ranges from (60) piasters to a JD. Allah, The Almighty, Says (what means): “O ye who believe! Fasting is prescribed to you as it was prescribed to those before you, that ye may (learn) self-restraint,- (Fasting) for a fixed number of days; but if any of you is ill, or on a journey, the prescribed number (Should be made up) from days later. For those who can do it (With hardship), is a ransom, the feeding of one that is indigent. But he that will give more, of his own free will,- it is better for him. And it is better for you that ye fast, if ye only knew.”{Al-Baqarah/183,184}. “

For those who can do it (With hardship), is a ransom,” Ibn Abbass (May Allah be pleased with them) said: "that this verse is meant as a concession for old men and ‏women who have no strength to fast as well as sick people who are not expected to be cured, so they should ‎feed one poor person for each day‏ ‏of fasting (instead of ‎fasting)." [Tafseer Ibn Ktheer].

Therefore, if you (questioner) suffer from an incurable disease, then you must estimate the missed fasts and pay the aforesaid ransom to needy Muslim persons. To be on the safe side, you should consider Ramadan as (30) days instead of (29).

ransom

However, if you were able to determine the number of missed fasts of former years, then you will be more rewarded by Allah. And Allah knows best.