Good afternoon everyone! I have a question regarding the risk free rate of my two asset portfolio. For my course, we have to create a two asset portfolio with the time frame of 2015-2020 with monthly returns. For the risk free rate, I have utilised the 5 year T-Bill because it has the same maturity as the project and also does not have any reinvestment risk since the T-Bills are zero-coupon bonds. However, I am unsure about my approach for the monthly risk-free rate, which I need since all of my returns of my assets are also monthly.
As of now, I took the yield of a 5-year T-Bill calculated the average yield of a 5-year T-bill from 2015-2020. Since the yield of the T-Bills are denoted in yearly terms, I took the caculated average yield of those five years and plotted the number in the following formula:
monthly rf yield = LN(1+avg. annual rf yield)/12
This gave me the avg. monthly rf rate. Is this approach appropiate or should I approach this problem in a different way? Kind regards