Fast is obligatory for Muslim from dawn to dusk. He should be well aware about that factors which can break Fast. It is forbidden for him to eat even halal foods during Fasting. A drop of water also breaks the Fast. If a person tries to do fasting to gain Allah’s blessing then he should try to learn that how can he improve his efforts and obtain Allah’s best blessing for him.
Fast is the matter of a person intention to Allah Almighty. So his fast breaks when he intentionally
Makes Sexual relationship
Takes any medicine
If he breaks without any valid reason he will have to fast again and will have to pay fidya for breaking fast.
If anyone eats, drinks, vomits deliberately, performs any sexual relationship and takes any medicine unintentionally or by force with any solid reason and he knows he is fasting then his fast will not break.
When Fast automatically breaks and there is no fidya for breaking Fast, you only need to fast again as Qaza, there are these reasons:
Post Natal bleeding
When a person can break fast?
A person can break his fast in such illness which is severe to tolerate in Fasting. In this situation, Islam allows him to break fast and do Qaza after Ramadan, when he is stable.
Note: keep in mind this point if you miss your fast in Ramadan. Then it will remain due/qaza to you until you do that due fast. Otherwise you will be asked in life hereafter. So try to do proper fasting.