The money market yield, also known as the CD-equivalent yield, allows the quoted yield on a T-bill to be compared with an interest-bearing money market instrument. Money market yield uses 360 day year for calculation.
In our T-bill example, we can calculate MMY as follows:
MMY = (360*9.86%)/(360 – 90*9.86%) = 10.12%
We can also calculate MMY from HPY as MMY is just the annualized HPY on a 360-day year basis.
HPR = 2.53%
Days to maturity = 60
MMY = 2.53*360/90 = 10.11%