1- If one is not sure whether or not he has missed prayers, he does not have to make up for any.[1] However, if he is sure that he has missed prayers, but he is not sure how many he has (and cannot guess either), then he must make up for the minimum number he is sure about.[2]

2- If one is not sure whether or not he has missed fasts, he does not have to make up for any. Once again, if he has a doubt in regard to the number, the rulings of the maraj’ are as follows:

Ayatullah Khamenei: “He only has to make up for the number of fasts he is sure he has missed.”[3]

Ayatullah Fadhel Lankarani: “If one is not sure how many fasts he has not carried out, he must make up for the number that he is sure he has missed, for example, if there is a doubt between five and seven fasts, he is only obligated to make up for five.”[4]

Ayatullah Zanjani: “According to obligated precaution, he must make up for the highest number that he thinks he has missed. (Therefore, if he has a doubt between five and seven, he must perform seven according to obligatory precaution.)”[5]

Ayatullah Makarem Shirazi: “He must make up for the number that he is sure he has missed.”[6]

Ayatullah Bahjat: “He must make up for the highest number that he thinks he may have missed.”[7]

3- If one intentionally neglects fasting during Ramadhan (without having any excuse such as being sick), he must make up for it and also fast two months for each day or feed 60 poor people or free a servant. If he does not make up for it till next Ramadhan, he must give an additional mudd of food to a poor individual.[8]

So, If he does not fast, because of being sick during Ramadhan, and his sickness continues till the next Ramadhan, he is no longer obligated to make up for the days he has not fasted, instead he must give one mudd (approximately 750 grams) of food (wheat, oat, etc.) to a poor individual for each day.

However, if he does not fast because of traveling, he must make up for the missed days and also give one mudd of food for each day to a poor individual.

Finally, if he has no excuse such as traveling or being sick, he must make for the missed days, pay kaffarah and also give one mudd of food for each day to a poor individual.[9]

Ayatullah Hadavi Tehrani’s answer to this question is as follows:

1- If one is not sure whether or not he has missed any prayers, he does not have to make up for any. However, if he knows he has missed some prayers and is not sure how many, then he is required to make for the number of which he is sure he has missed.

Therefore, if he has a doubt between two or five prayers, he is only required to make up for two. If he also has a doubt in regard to what prayers they were, he would have to practice precaution. In other words, if he has a doubt between two fajr prayers and three maghrib prayers, he must make up for all of them.

2- If one is not sure whether or not he has missed any fasts, he does not have to make up for any. However, if he knows he has missed some prayers and is not sure how many, then he is required to make for the number of which he is sure he has missed.

3- One who does not fast during the month of Ramadhan must pay the kaffarah of delaying unless his excuse continues until the next Ramadhan. In that case, he does not have to make up for them, but he does have to pay the kaffarah of unintentionally breaking the fast.

Related websites:

Making up for the fast of the holy month of Ramadhan, 9150 (site: 9132).

Paying kaffarah by the Ramadhan of the next year, 5847 (site: 6065).

The kaffarah of the fast, 1965 (site: 1990)

Link to the Istifta’at page, (code: 240)