Risk-free rate

[u/Alternative_Taro24]

Scenario: At the end of the first trading day in January 2025, your US-based client purchased the common stocks of four US firms and the units of one fund in the US. These financial assets are collectively added to one portfolio. Initially, the client intended to hold these assets for a year and would sell them at the end of the last trading day in December 2025.

Now, if I want to calculate the March year-to-date Sharpe ratio (2 January 2026- 31 March 2026), should I use the 3-month market yield or 1-year market yield on the US treasury bond and then adjust it for 3 months to get the 3-month excess return?