All perfect praise be to Allaah, The Lord of the Worlds. I testify that there is none worthy of worship except Allaah, and that Muhammad is His slave and Messenger. We ask Allaah to exalt his mention as well as that of his family and all his companions.
It appears from your question that this deposit is in reality an investment deposit or what is called a business certificate.
We have already issued Fatwa: 84586 explaining the ruling of investment certificates, their kinds, and the conditions for their permissibility, so please refer to the Fatwa for more benefit.
If the deposit that you are inquiring about is free from any religious prohibition then Zakat has to be paid on it and on the profit thereof when a complete year elapses on the capital money which you did not spend during the year, based on two conditions:
1) It should reach the minimum amount liable for Zakat by itself or with other money, tradable items, gold or silver added to it.
2) A whole lunar year should have elapsed on it.
Therefore, if it reaches the minimum amount liable for Zakat and a whole lunar year has elapsed on it, then Zakat has to be paid on it at each year when these two conditions are met. The rate of Zakat is 2.5%. For more benefit on Zakat on invested money, please refer to Fatwa: 83529.
Allaah knows best.