the question is utterly wrong. whoever made it is a jackass...
to begin with dowry is not a concept in Islam, its a subcontinent phenomena adopted/continued by Muslims, as in Hinduism the women have no right over heritage property/assets so it was custom that whenever possible the parents/relatives would give unmarried girls gifts and upon marriage dowry which was all she was to get from her parents/relatives but no share in property or assets...
whereas, in Islam there is no concept of dowry... the only incident which the so called scholars pull out as leverage for dowry is when Prophet Muhammad gave some household stuff to Hazrat Fatima upon her marriage... so a minimum amount of dowry is set with reference to it.
however, what they forget to mention is that the amount which Prophet Muhammad used to buy stuff for Hazrat Fatima was given to him by Hazrat Ali, who borrowed the money from a Jew, which was later paid off by some other companion friend of Ali to that Jew lender.
so, if you take into account full tradition, it gives no excuse to take dowry.
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now, to the right question. there are three types of Mahr; prompt deferred or both. it solely depends on the bride to decide which mood of payment she wants to adopt.
Prompt means Mahr paid/given upon Nikkah. if that is decided and groom doesnot obey, the wife has the right to deny her husband right of bed sharing.
Deferred means the Mahr which groom or his father promises to pay on a later date. it can be the house or anything as you may know. the Bride has the right to deny rights of bed sharing, untill she agrees the marriage cannot be consumed... wife can also forgive Mahr out of free will.
Prompt+Deferred is obviously the Mahr which is half paid upon Nikkah and half on agreed time, it can also be at time of divorce.
so if you understand this you know there is no concept of Dowry in Islam but there is a MUST Mahr for women.
another wrong concept spread by so called scholars is Sharai Mahr. this is utterly unfair. Mahr is to be decided by the girl. however, the amount/assets she demand should be payable by interested man or his father. usually Mahr is said to be twice as much as a man's earning of a month, which is also not fixed.
Mahr can be anything which a girl wishes or demands upon invitation for marriage.