How to Count Menstruation

السلام عليكم و رحمة اللّٰه و بركاته

I hope you are well.

I am aware that menstruation/haidh is regarded as bleeding between 3 – 10 days (maximum). However, how does one count days and is ghusl performed on the 10th day or the 11th day? The reason for my question is sometimes I find that I bleed on the 10th day but I am unsure if that is actually the 10th day or the 11th day due to the question below.

For example, if haidh started on a Saturday, will we count days based on the solar calendar, therefore day 10 will be the second Monday? Or will we count based on lunar calendar, and therefore haidh started on Saturday before Maghrib (or Friday after Maghrib) and therefore day 10 will Be Sunday After Maghrib?

If solar is correct, will ghusl be performed on the Monday (day 10) or on the Tuesday? Or if lunar is correct, will
Ghusl be performed on Sunday After Maghrib or Monday after Maghrib?

Answer

In the name of Allah, the Inspirer of truth

A day in menstruation (hayd) or post-natal bleeding (nifas) is not counted based on the lunar or solar calendars. One day is counted as a complete 24 hours from the time bleeding begins. Therefore, three days will be 72 hours and ten days will be 240 hours.

In the example you have used, the time hayd begins will be taken into consideration in counting the days. For example, if hayd began at 10.30 am on Saturday, then one day will be completed at 10.30 am on Sunday. Counting in this way, ten days will be completed at 10.30 am on the second Tuesday, which is when a ritual bath (ghusl) will be performed if bleeding continues.

And Allah knows best.