SHAFAQNA – The Grand Ayatollah Sistani answered a question about compensating for missed fasting days on purpose.
Question: What is the ruling when fasting days missed on purpose?
The Grand Ayatollah Sistani: Missed fasting days must be compensated for by fasting (to the number of days missed later on), and if someone carries out an act which makes fasting void whilst is aware that act makes fasting void, in addition to fasting that day (later on) Kaffarah also becomes Wajib for that person. And also, according to Wajib precaution, this also applies to a person who is unaware of the ruling but has no excuse about his unawareness, and is not sure either; meaning that person considers it probable that (his/her) fasting is void. But if a person is not aware of the ruling and has excuse about his unawareness, or is sure that act does not make fasting void, Kaffarah is not Wajib for this person; but if is aware that (his/her fasting) is void, and does not know about Kaffarah, must pay Kaffarah.
And for Kaffarah of one day of Ramadhan, it is sufficient to feed sixty poor persons to the amount of 750 grams each equal to wheat, or bread, or similar to them. And if knew that must compensate (for each day by fasting later on) and delays it by one year till the next Ramadhan, must compensate by fasting each day missed as well as feeding a poor 750 grams equal to wheat, or bread; and if it is delayed more than a year, Kaffarah is not repeated. And if there is uncertainty about the number of days to compensate, the lower number will suffice.
Source: PERSIAN SHAFAQNA