I am trying to identify best practices when it comes to Treasury Bill yield calculations. Without getting too granular, our calculation will use 365 days unless Feb 29 is between settlement date and maturity date, then 366. Others have said if Feb 29 is within 1 year after issue date, regardless of maturity date, use 366. Which is correct? I am struggling with how you calculate to a leap year when the bill matures prior to the leap year.