Common Mode Cutoff Frequency ($f_{cm}$):

Formed by the Common Mode Choke ($L_c$) and the Y-capacitors ($C_y$) to Earth.

$f_{cm} = \frac{1}{2\pi \sqrt{L_c \cdot (2 \cdot C_y)}}$

Differential Mode Cutoff Frequency ($f_{dm}$):

Formed by the leakage inductance of the choke ($L_d$) and the X-capacitor ($C_x$). Usually $L_d$ is 0.5% to 2% of $L_c$.

$f_{dm} = \frac{1}{2\pi \sqrt{2 \cdot L_d \cdot C_x}}$