The first condition for one to be obligated to fast is to be Muslim.
In this world the non-Muslim is not requested to fast; however, in the
Hereafter, he will be punished for neglecting to fast–as he will be
punished for his blasphemy. Rather, the obligation on the non-Muslim is
to embrace Islam, then among many obligations, is to fast Ramadan.
Secondly, it is the pubescent Muslim who is obligated to
fast. The child is not obligated to fast. However it is an obligation
on the parents or the guardian of the child to order him or her to fast
once he/she is 7 (lunar) years old, with the condition that the child’s
body can withstand that fasting, and he would not be harmed by it.
Also, for one to be obligated to fast, he must be of sound mind. Fasting is not obligatory on the insane person.
Fasting is not obligatory on a person whose body cannot
tolerate fasting, either due to old age or because of a severe illness.
Moreover, if a person would be harmed by fasting, that is, as a result
of his fasting his sickness would get worse or he would die, then
fasting is prohibited for him. The one who does not fast because of old
age or an illness he is not hopeful to be cured of, does not have to
make up the missed days of fasting. Instead, he pays an expiation to a
poor Muslim for every day of fasting he missed. He can pay the
expiation for every day to the same person or he can choose different
people to pay to. The expiation is two cupped (average-sized) handfuls
of the most common staple food of the town. In the United States, for
example, the most common staple food is wheat.
Fasting is not obligatory on the menstruating woman or the woman who is
in her postpartum bleeding period. In fact, it is unlawful for them to
fast. The woman who missed days of fasting during Ramadan for these
reasons has to make up each missed day.
In addition
to the aforementioned, the pregnant woman is allowed not to fast if she
fears harm would come to her or her baby from her fasting. This
includes the breast-feeding woman as well. She is allowed not to fast
if she fears harm would come to her or her baby from her fasting. Both
must make up every missed day of fasting. If the reason a woman did not
fast was solely the fear of harming her baby, then in addition to
making up the missed days of fasting, she must pay an expiation This
expiation is two cupped, average-sized handfuls of the most common
staple food of the country, for each day she missed.
The one who is traveling a distance of two or more walking days is
allowed not to fast–provided his traveling is not sinful. Two or more
walking days distance is about 80 statute miles. This traveler is
permitted to break his fast even though he would not encounter hardship
during his trip‑‑as would be the case if he crossed this distance
quickly, by plane, or comfortably, in a car or a train. The matter of
traveling is not based on the hardship; rather, it has to do with the
distance. This facility for the traveler was mentioned in the Qur’an.
Allahsaid in Surat al-Baqarah, Verse 185:
{ وَمَنْ كانَ مَرِيضاً أوْ عَلَى سَفَرٍ فَعِدَّةٌ مِنْ أَيَّامٍ أُخَر }
which
means: (If you are sick or traveling, then you are allowed to
break your fast and make up these days later.)