I want to know what are the rulings underlying mehr? the types of mehr? how it is calculated?

Answer

Wa alaikumus salaam

Mahr (dowry) is something having commercial value according to shariah, which the bride is entitled to claim from the bridegroom in virtue of nikah.

It may be something that is specified at the time of nikah and is called Mahr Musammah (specified Mahr). Mahr Musammah may be agreed upon between parties to be paid at the time of nikah and is termed as معجل (Mou’ajjal). And it may be paid later at a time agreed and convened between parties and is called مؤجل.It may be partly معجل and partly مؤجل.In case nothing has been decided about the mode of payment, it should be understood that it should be paid immediately and promptly at the time of nikah.

The minimum value of Mahr should not be less than 10 dirham or its equivalent at the place where the nikah is performed unless stated otherwise and there is no limit of its maximum.