Does fasting break if your gums bleed?

Whether bleeding from the gums breaks the fast depends on the amount of blood. If a large amount of blood flows and you swallow it without noticing, your fast is broken. You must then make up that day later. If only a small amount of blood comes out, it does not break the fast.

The amount of blood is determined by comparing it to saliva. If the blood is equal to or more than the saliva, it is considered “a lot.” If the blood is less than half of the saliva, it is considered “a little.”

The book Radd al-Muhtar states: “If blood comes out from between the teeth and reaches the mouth but is not swallowed, the fast is not broken. But if the amount of blood is a lot or equal to the saliva and is swallowed, the fast is broken. If it is a little, the fast is not broken.” [1]

From the book "Fatwas Regarding Ramadan Fasting"

[1] Hashiyat Ibn Abidin, 3/368.