A sick person and a traveler  are allowed to break their fast in Ramadaan. They must make up the days that they missed (by fasting other days) at a later time, even if the days are not fasted consecutively. Allaah says:
“Whoever is ill or on a journey, then (he may break the fast and instead fast) the same number of days missed, on other days. Allaah wishes for you ease and He does not want to make things difficult for you.” [Surah Al-Baqarah: 185]
Those who are not able to fast, such as the elderly man and elderly woman (past age of childbearing),  may break their fast and instead feed a needy person for every day that is missed. This is due to their falling under the saying of Allaah:
“And as for those who cannot fast (because of difficulty) they may feed a needy person (for each day missed)”
based on the interpretation (of this ayah) found in authentic narrations of some of the Companions. As a matter of fact, this happened to one of the Companions, for Anas Ibn Maalik (رضي الله عنه) reported that
“he was weak one year and could not fast. So he made a bowl of porridge and called thirty needy people and fed them.” [Reported by Ad-Daraqutnee with an authentic chain of narration]
If a pregnant woman or a breast-feeding woman fears for herself or for her children, she may break her fast and instead feed a needy person for each day missed. This is based on her falling under the generality of the ruling found in the previous ayah. And according to the most correct opinion,  these two women do not have to make up for the missed days of fasting (i.e. by fasting other days).
It is not permissible for a menstruating woman and a postpartum bleeding woman to observe the fast until they stop bleeding. So when they stop bleeding, they must make up for the days of fasting they missed. And they do not have to make up for the prayers they missed during that time,  as is authentically established in the Prophet's Sunnah, where he said:
“Is it not true that when a woman is menstruating, she neither prays nor fasts?” [Part of a hadeeth reported by Al-Bukhaaree]
Anyone that eats or drinks out of forgetfulness is not obligated to make up for a missed day or to expiate. Rather, he must just complete his fasting (for that day). The Prophet (صلى الله علیه وسلم) said:
“Whoever forgets while he is fasting and eats or drinks, then let him complete his fast, for it was indeed Allaah who fed him and gave him to drink.” [Reported by Al-Bukhaaree and Muslim]
The ruling for anyone who breaks the fast due to a mistake  or because he is forced to is the same ruling as that of the one who breaks his fast out of forgetfulness. This is based on the generality of the Prophet's (صلى الله علیه وسلم) saying:
“Verily, Allaah has excused for my ummah (sins they commit due to) mistakes, forgetfulness and what they are forced to do.” [Reported by Ibn Maajah and others, and it is authentic due to all of its paths of narration]
Whoever eats or drinks intentionally during the day in Ramadaan without any valid excuse that allows him to do that has committed a sin and has nullified his fast. It is obligatory on him to repent from that great sin and to make up that missed day of fasting.
Anyone that has sexual intercourse with his wife during the day in Ramadaan, while they are both fasting, both of their fasts are broken. And it is obligatory for both of them or (perhaps) one of them to repent. And they must both make up that broken day of fasting and he must do the expiation (kaffaarah). The expiation is freeing a slave. If it is not possible to find a slave, then he must fast two consecutive months. If he is not able to do that, then he must feed sixty needy people, as is stated in the story of the man who had sexual intercourse with his wife during the day in Ramadaan. [Reported by Al-Bukhaaree]
And in some narrations of the hadeeth, other than that of Al-Bukhaaree's, there is a command to make up for the missed day of fasting. [Authenticated by Al-Haafidh Ibn Hajr in Fath-ul-Baaree]
There is no harm in a person tasting food with his tongue, while he is fasting, on the condition that nothing enters (his throat). This is since it is not truthful to say that a person who tastes food is in fact eating or drinking.
 No one is permitted to break the fast and make it up another day except these two, since Allaah did not mention a text for anyone besides them. “And your Lord is not forgetful.” So the fatwa given by some contemporary (scholars) that it is permitted for school and college students to break their fast during examination times, and also for those people who have hard-labor occupations is not correct.
 And likewise the sick person that has a chronic disease – who is not able to fast with it, nor is it expected that he will be cured in the confines of the means that Allaah has enabled.
 This is the opinion of Ibn ‘Abbaas and Ibn’Umar (radi-Allaahu 'anhumaa). And it is not known that any of the other Companions opposed them in that. For a further discussion on this, refer to the book “Fasting in Ramadaan” of Shaykh Saleem Al-Hilaalee and ‘Alee Hasan ‘Alee Abdul Hameed Al-Halabee.
 What some women do – such as intentionally leaving off food and drink during the condition of menses, then taking a sip of water before sunset – has no basis to it. Rather it is in opposition to the Sunnah.
 Such as the one who thinks it is still nighttime and thus eats. Then it becomes clear to him that the sun has risen, and that it is Fajr. Or like the one who hears the Aadhaan over the radio and thus breaks his fast, but finds out that it is an Adhaan from another country that has a different timing.