Does involuntary vomiting break the fast?

Involuntary vomiting does not break the fast. This is the position of the majority of scholars across the four major schools of Islamic jurisprudence (Ḥanafī, Mālikī, Shāfiʿī, and Ḥanbalī), based on the ḥadīth:

“Whoever is overcome by vomiting is not required to make up the fast, but whoever vomits deliberately must make it up.” — Reported by Abū Dāwūd, al-Tirmidhī, Ibn Mājah

Key Distinctions

• Involuntary vomiting: Does not break the fast — no expiation or make-up required
• Deliberate vomiting: Breaks the fast if a mouthful (malʾ al-fam) is expelled — make-up required but no expiation (kaffārah)

One should avoid swallowing anything that returns to the throat and, if possible, rinse the mouth afterwards without swallowing water.