Quick answer
Can I fast before ghusl after my period ends?
Yes. If your period ends during the night and you make the intention to fast, your fast is valid even if you have not yet performed ghusl by fajr. You still must perform ghusl in order to pray — but the fast itself is sound.
Yes. If ḥayḍ ends before fajr and you intend to fast, the fast is valid even if you have not performed ghusl by the time fajr enters. This is established by analogy with the one in a state of janābah: ʿĀʾishah and Umm Salamah (raḍiyallāhu ʿanhumā) reported that the Prophet ﷺ would enter the morning in a state of janābah from intimacy, then perform ghusl and fast. (Sahih al-Bukhari, Sahih Muslim)
The condition is that the bleeding has genuinely stopped before fajr. If even a moment of fajr enters while you are still in ḥayḍ, you are not fasting that day — that day is made up later — because part of the fasting time fell within menstruation.
Although the fast is valid before ghusl, you must still perform ghusl al-ḥayḍ in order to pray. Do not delay ghusl needlessly: perform it promptly so the fajr prayer is not missed. The fast and the prayer are separate obligations — purity of the fast does not require ghusl first, but prayer does.
In short: end of bleeding before fajr + intention to fast = a valid fast, even with ghusl performed after sunrise. Noor helps you log when purity returned and reminds you to perform ghusl for prayer while confirming your fast for the day stands.
This summary draws on the established positions of the four Sunni madhhabs. For your specific situation, consult a qualified scholar.
Go deeper
Making up missed fasts in Ramadan