If a woman is not sure whether a fast is obligatory or not in her case, then she intends to fast with an uncertain intention: if she owes any fasts, then this will be making up a fast, and if she does not owe any fasts, then her fast will be naafil. In that case her fast will be valid and will make up the missed fast, if she owed any fasts for days that she missed in Ramadan. However, what she should do is not make this the case in all of her fasts. Rather she should try to work out the number of days that she fears she must make up from the past, and try hard to absolve herself, thenmake a certain intention for her fast: either to make up for a missed fast or to observe a naafil fast. … She should not open the door to intrusive thoughts (waswasah) and doubts and uncertainty about her acts of worship. And Allah knows best.

• Whoever breaks the fast – even for one day – with no excuse has committed a major sin and has exposed himself to the wrath and punishment of Allah. • Whoever openly breaks the fast should be given a disciplinary punishment by the ruler, a punishment that will deter him and others like him from doing this grave act.

If a person intentionally misses Ramadan fasting, he must make them up according to the view of most of the scholars. For more, please see the detailed answer.