Upon menstruation should one break her fast immediately, if it is afternoon, wait until Iftaar?

Praise be to Allah, the Lord of the Worlds; and may His blessings and peace be upon our Prophet Muhammad and upon all his Family and Companions.

If a woman during Ramadan has menstruation during the day, her fasting should be interrupted immediately.  And if she keeps on fasting after the menstruation period has started, then her fasting is null and invalid.  Moreover, she should make up for this day and all other days of menstruation.

Ibn Qudamah has mentioned in ‘Al-Mughni’: 'There is a consensus of scholars that a woman having menstruation and a woman that has given birth should break the fast and it is not permissible for them to fast.  If they fast (in this condition), their fasting is not accepted.  But they should make it up (once the period of impurity is over).'

Ayisha (Radiya Allahu Anha) said (that woman used to be in a state of impurity (menstruation) at the time of the Prophet (Sallallahu Alaihi wa Sallam) and they were ordered to make up for any fasting days they missed, but were not ordered to make up for the prayers they missed during that period). [Narrated by Bukhari and Muslim].  The order in this Hadith is given by the Prophet (Sallallahu Alaihi wa Sallam).  Abu Said stated that the Prophet (Sallallahu Alaihi wa Sallam) said: "Is it not that a woman among yourselves if she is in menstruation, she does not fast and does not pray, this is (an evidence) of a lack of her religion." [Narrated by Al Bukhari]

Allah knows best.