Optimizing the net interest margin of a bank : An extension of the Black-Litterman model with financial regulations

Sammanfattning: A bank's business model is based on borrowing and lending, and by borrowing funds at a lower rate and lending these funds at a higher rate, the bank makes a profit. Thus, a key task in each bank's operations is to maximize its net interest margin. In addition, in optimizing the net interest margin, banks must take into account financial regulations, among others the Net Stable Funding Ratio (NSFR). In cooperation with Handelsbanken, this bachelor thesis in applied mathematics and industrial engineering aims to examine how the bank's net interest margin can be optimized. The Black-Litterman model, an asset allocation model, is used and modified in order to model the bank's balance sheet. Historical data of Swedish government bonds serves to estimate the variances and covariances of the bond returns. From there, two approaches are used to model the returns, the first assuming that the bonds are held to maturity and the second assuming that the bonds are held for trading. The results show that bond returns cannot be approximated with a normal distribution when held to maturity. Thus, a fundamental assumption of the Black-Litterman model is violated. Instead, the thesis concludes that the bank's net interest margin can be optimized with the Black-Litterman model only if it is assumed that the bank's balance sheet is a portfolio of bonds where the bonds are held for trading. Further, in order to ensure that the requirements of the NSFR are met, the NSFR can be incorporated into the model as a constraint.