Conditions for not keeping fast

Fear of illness getting worse or loss of life
Ruling: If one is so ill that fasting will be injurious to his health or there is fear that if he will fast the illness will become aggravated or it may be prolonged, then such a person may not keep fast. He should offer compensatory fast after recovery. But it is not proper to give up fasting merely upon one's own guess. A pious Muslim hakim or doctor must be consulted.

Ruling: If the hakim or doctor is a non-believer or does not follow the religious code, his advice should not be trusted and fast should not be given up.

Ruling: If on personal experience some symptoms occur which convince one that fasting will be harmful to him, then such a person may give up fasting. But if one has no personal experience or is not aware of the causes of his illness, then fast should not be given up on one's own guess. If not on the advice of a pious doctor but on one's own experience a fast is broken, then Kaffara will have to be given. And if the fast was not kept at all, then only Qadha and not Kaffara will be due.

Ruling: A person has recovered from illness but is still weak and it is feared that the illness will recur if he fasts, then it is permissible for him not to keep it.
Journey

Ruling: If a person is on a course of journey, it is permissible for him not to keep the fast and offer its Qadha later on.

Ruling: If a traveler has no trouble during the journey as for example he is traveling on a train and hopes to reach home by the evening or he has all the means of comfort during the journey, then it is better for him to keep the fast.
If he does not keep the fast and offers Qadha instead, then it is also permissible and there is no sin in it. However, in that case, he will be deprived of the blessings and merits of Ramadan fasting. If one faces hardships during the journey due to fasting, then it is better not to keep the fast.

Ruling: If any one did not recover from illness and died or a traveler died during the journey, then there will be no interrogation about the fasts missed during illness or journey because he did not get the time to offer their Qadha.

Ruling: If a person during his course of journey stops at a place with the intention of staying there for fifteen days, then it is not right to miss the fasts because he is now no longer a traveler. But if the intention is to stay for less than fifteen days, then it is permissible not to keep fasts.

Ruling about pregnant women and those suckling a baby

Ruling: A pregnant woman or one suckling a baby may not fast if there is fear of her own-life or that of the baby. She should keep the missed fast later. But if her husband has the means to engage a wet nurse and relieve the wife, then it will not be permissible for the wife to give up fasts. If on the other hand, a baby is of such a nature that it will not take milk from anyone else except its mother then it is permissible for her to give up fasts.