The document proposes a new mathematical model for musyarakah (joint venture) contracts in Islamic banking. The model allows for two different profit sharing rates between the bank and customer. This addresses limitations in previous models that used a single rate, which could be unfair to one party. The document applies the new model to a sample musyarakah product over 6 months with changing profit rates. The results show the new model distributing profits fairly between the bank and customer compared to previous models. This could encourage banks to offer more musyarakah products and promote equity-based contracts in Islamic finance.