Fasting laws

1- What is the ruling when someone does not know how many fasts or prayers he has to make up for from previous years?
2- What is the ruling if one delays making up for fasting until the next month of Ramadhan? Does he have to pay kaffarah in such a case?
3- Is it permissible to delay fasting missed fasts from last Ramadhan until after the next Ramadhan?

1- If one is not sure whether or not he has missed prayers, he does not have to make up for any.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- If one is not sure whether or not he has missed fasts, he does not have to make up for any. 
 “He only has to make up for the number of fasts he is sure he has missed.”

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.

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.

Source: http://www.islamquest.net/en/archive/question/fa9411