Question
If one has missed fasts from many past Ramadans, are they required to make-up all the previous fasts or does it suffice them to makeup the fasts of only one Ramadan?
Answer
In the Name of Allah, the Most Merciful and Compassionate
If one has missed fasts, either from one Ramadan or many, it is obligatory for them to makeup every individual day missed. [Tahtawi/Shurunbulali, Hashiyat Maraqi al-Falah]
You may be confusing this specific issue with that of expiations (kaffarat). Unpaid expiations from multiple past Ramadans are joined together (combined as one) and one expiation suffices for all; that is as long as none of the previous expiations were paid. This does not apply to the making up of the fasts. Making up the fasts remains an obligation. [Ibn ‘Abidin, Radd al-Muhtar]
Hope this helps
Allah knows best
[Shaykh] Yusuf Weltch
Checked and Approved by Shaykh Faraz Rabbani