Allah says:

Meaning: Whoever is ill or travelling must make up the same number on other days. Allah intends ease for you, not hardship. Al-Baqarah 2:185, excerpt.

Anas ibn Malik al-Kabi, may Allah be pleased with him, reported that the Prophet said:

Meaning: Allah has waived half the prayer and fasting for the traveller, and fasting for the pregnant and breastfeeding woman. Al-Nasai 2274. Al-Tirmidhi also narrated the report, 715, and graded it hasan. This narrator is Anas al-Kabi, not the well-known Anas ibn Malik who served the Prophet.

The report establishes the fasting concession. Ibn Baz treated pregnant and breastfeeding women like the ill person or traveller who makes up missed fasts when able. Shortening prayer in this report is a travel ruling; pregnancy or breastfeeding does not itself permit shortening prayers.

For fasting's basic obligation, conditions and intention, see Ramadan Fasting for Beginners.

If she can fast without harm or unusual hardship and has no other valid excuse, she must fast. The ruling depends on how fasting affects her and her child, not simply on being pregnant or breastfeeding.

She may break the fast if it causes significant hardship or there is a well-founded fear of harm to herself, her unborn baby or her nursing child. Clear previous experience, apparent signs or a trustworthy clinical assessment may establish this; she need not wait for harm to occur.

Ordinary tiredness, hunger or thirst does not by itself excuse everyone from fasting. Yet what is ordinary for one woman may signal a problem for another. Someone else's experience of fasting throughout pregnancy or breastfeeding cannot decide your case.

Under the preferred ruling followed here, she makes up one day for each day missed through the excuse when she is able. Feeding is not additionally required merely because she missed the fast through pregnancy or breastfeeding. Ibn Baz gave this ruling whether the concern was for the woman or her child, treating the excuse like an illness from which recovery is expected.

For example, someone who misses ten days because pregnancy makes fasting difficult makes up ten days when able. Taking this lawful concession does not require a kaffarah of fasting two consecutive months. Nor may someone able to make up the days simply choose a payment instead.

Someone whose excuse continues, preventing her from making up the days before another Ramadan, is not sinful for that excused delay. Under Ibn Baz's ruling, she does not owe feeding because of it. The missed days remain owed until she can make them up.

Pregnancy may be followed by breastfeeding and then another pregnancy. She need not fast through harm merely to stop the number growing. But the passage of years does not cancel qada or automatically make her permanently unable to fast. When she can fast without a continuing excuse, she makes up what she can, even on separate days. Ibn Baz expressly advised making up days according to ability in this situation.

If a new Ramadan arrives and she can fast, she fasts the current Ramadan, then returns to making up the older days. If a valid excuse remains, its ruling still applies.

Lasting inability from which recovery is not expected has a different ruling. Someone whose medical condition makes fasting permanently unmanageable, on a trustworthy assessment, feeds a poor person for each day, as scholars explain. Being pregnant or breastfeeding, or having many days to make up, does not by itself establish that lasting inability.

If a lasting illness develops, seek advice about your circumstances and the days already owed, explaining the medical assessment. Not every condition called chronic means fasting is impossible at all times; the person may be able to make up days at another time.

Make up the days after the excuse ends, according to your ability. They do not have to be consecutive. You may fast one day and leave gaps, or choose shorter days, while completing the obligation within its time if able. Weaning is not a prerequisite if you can make up days while breastfeeding without harm or significant hardship.

Aishah, may Allah be pleased with her, said:

Meaning: I would have fasts owed from Ramadan and could not make them up until Shaban. Al-Bukhari 1950. This shows the allowance to make up days before the next Ramadan, not permission to delay beyond it without an excuse.

Qada is obligatory fasting, so resolve in your heart before dawn to fast the next day as qada, without a spoken intention formula. The Prophet said:

Meaning: Whoever does not resolve to fast before dawn has no fast. Abu Dawud 2454, authenticated by al-Albani. It is applied here to obligatory fasting.

Once you begin a qada fast, you must complete it rather than stop simply because you would prefer to postpone it. But if illness or another valid excuse permits breaking the fast, you may do so, as Ibn Baz explained, and fast that day later when able. Qada being obligatory does not require continuing through serious harm.

Ramadan qada is not valid on either Eid day or the days of Tashriq. The specific Tashriq exception concerns pilgrimage fasting for someone unable to obtain the hady, not making up Ramadan. Al-Bukhari 1991 and 1997.