How do I make up for many years of fasting, do I start from the last one or the first one? And what are the conditions for the intention to make up for fasts, and what invalidates them?

If breaking the fast in Ramadan is without a legitimate excuse, the Muslim must repent to Allah and make up the missed days, along with feeding a poor person for each day if able. Otherwise, repentance and making up the days are sufficient. If one delays making up the days until another Ramadan begins without an excuse, then according to the most preponderant opinion, a fidyah (expiation) is required along with making up the days.

It is necessary to make up the number of days you did not fast. If you are not sure of the number, continue making up days until you are reasonably certain that your obligation has been fulfilled. It is preferable to make up the days in chronological order.

For the intention of making up fasts, it is a condition to specify the intention, and for it to occur at night before dawn according to the majority of scholars, and for it to be decisive. Among the things that invalidate the intention are its indecisiveness, its occurrence after dawn, not specifying that it is for making up Ramadan, or intending to break the fast while fasting.