What is the ruling on determining the sex of the fetus by computational methods, such as adding the number of days of the month in which menstruation occurred with the number of days of the month in which birth is expected, in addition to the sum of the letters of the mother's and grandmother's names, and then deducing the sex of the fetus based on whether the result is odd or even?

It is not permissible to rely on methods similar to the Chinese Gender Chart to determine the sex of a fetus or to know any unseen matter. This falls under the actions of soothsayers and astrologers, which is among the gravest prohibitions and an odious form of shirk (associating partners with Allah), for Allah alone knows the unseen, and to Him belongs creation and command. Anyone who relies on a means that Sharia has not made a means is committing minor shirk. This method makes the calculation of days of months and letters of names a means to know the unseen without Sharia-based or sensory permission. Therefore, one must beware of it due to the blemish it causes in a Muslim's belief.