What is the equivalent of 400 Dirhams in today's circulating currencies, and is it permissible for me to inform my fiancée of the designated amount for the dowry to help her prepare herself and expedite the marriage?

There is no religious text that specifies the maximum or minimum mahr (dowry). However, it is recommended that the mahr not exceed five hundred silver dirhams, which was the dowry of the Prophet's wives (peace be upon him). This amount is equivalent to 1487.5 grams of silver. There is no harm in informing the fiancée of this. If the husband increases this amount with the intention of helping her, he will be rewarded, especially if it is to expedite the wedding and enable both parties to live a chaste life.