The Official Website of Grand Ayatollah Makarem Shirazi

Several groups of Muslims are allowed not to observe fasting. First of all, boys and girls who have not yet reached the age of Shari puberty. However, those girls who have just reached the age of puberty and are not able to fast do not have to do so. Even if they do not become able to fast until the Ramadan of the following year, it is not incumbent upon them to perform the qada of the missed fast. And all they have to do is give one mode of food to a needy person for each missed fast. If a girl has the ability to fast but she breaks her fast because of being forced by her parents to do so, she must perform the qada of the missed fast later. But based on obligatory precaution, her parents are obliged to observe the amd kaffārah. The second group is the elderly who find it excessively difficult to fast. If they can fast in a season with mild weather after Ramadan, they should make up for the missed fast based on the precaution. But in the event that they cannot fast until the following year, they no longer have to make up for the missed fast and it is sufficient for them to give one mode of food to a needy person for each fast they have missed. The third group of people who are not obligated to observe fasting are pregnant women for whom or for whose fetus fasting is harmful. In that case, if fasting is harmful for them alone, it is sufficient to perform the qada of the missed fast later. Furthermore, if they cannot fast until the following year, they do not have to perform the qada of fast either and giving kaffārah is sufficient for them. Nevertheless, if pregnant women's fasting would cause harm to the fetus, they should both perform the qada of the missed fast and give kaffārah after childbirth. The fourth group is women who are breastfeeding their babies and fasting can do harm to either themselves or their babies. However, they should both make up for the missed fast and also give one mode of food as kaffārah whenever they can. But if fasting is harmful for themselves, they should only make up for the missed fast whenever they can and if they cannot fast until the following year, only kaffārah is due on them. Nevertheless, if such mothers are able to find someone who can breastfeed their baby without charging them any money or being beholden to her, then they are obligated to fast.