|As salaam-o-alaikum Wa Rehmarullahe Wa Barakatahu
If someone is unable to fast during Ramadhan due to health conditions or old age, what is the alternate he or she can do so as to get the blessings of Ramadhan.
In the Name of Allah, the Most Gracious, the Most Merciful.
As-salāmu ‘alaykum wa-rahmatullāhi wa-barakātuh.
In principle, if one is unable to fast because of a temporary sickness, he/she is required to make up for the missed fasts upon recovery.
However, if one is unable to fast due to a permanent illness or old age, and there is no hope of regaining the ability to fast, then he/she must offer Fidyah (monetary compensation) for each missed fast.
The value of Fidyah for each fast is the same as Sadaqatul Fitr, which is currently $6.
Hence, for 30 days of missed fasts, one must give $180 to the poor and needy.
There are many A’maal one may do to gain the blessings of Ramadhan, such as recitation of Quran, Zikr of Kalimah and Istighfaar, Dua, giving Sadaqah and doing Ta’leem of books such as Fadhaail A’maal especially the section on the Virtues of Ramadhan.
And Allah Ta’āla Knows Best
(Mufti) Abdul Azeem bin Abdur Rahman
 Masaail Rifat Qasmi, Vol. 4, page 166-169, Hamid Kutub Khana Karachi