Answered by Shaykh Faraz Rabbani
Is it permissible to recite loudly while praying fajr, maghrib, or ishaal one? what about reciting out loud during nawafil? if not, is tahajjud an exception or does even tahajjud have to be done silently (while praying alone)?
The one praying alone has a choice whether to recite aloud or silently in the prayers that the imam recites aloud in (fajr, maghrib, and isha), though it is necessary (wajib) for such an individual to recite quietly in the prayers that the imam recites silently in. Women, however, should not raise their voices such that non-mahram men may hear them.
As for supererogatory (nafl) prayers, it is best to recite daytime prayers quietly, and though one has a choice in nighttime prayers, it is better to raise one’s voice somewhat, without disturbing others.