How is the maintenance amount during the Iddat (of Talaaq) calculated?

Your husband should provide such an amount that would suffice in fulfilling your needs during the Iddah for which he is responsible such as your Nafaqah, food, drink, clothing and accommodation. This can be calculated by you, as it would differ depending on the area in which you reside.

However, if you voluntary leave your matrimonial home and chose to spend your Iddat at your parents home, then your husband is not liable to maintain you. Re:- Kitaabun Nawaazil Pg.243 Vol.10 The responsibility of him maintaining you during your Iddat period is only if you spend your Iddat at his residence.