Energy released in Radioactive decay process $X\to Y+y$ is equal to

By law of conservation of energy we get

$$\begin{gathered} m_x{c}^2+K_x=m_Y{c}^2+K_Y+m_y{c}^2+K_y \\ Q=\left(m_x{c}^2-m_Y{c}^2-m_Y{c}^2\right)=K_y+K_y-K_X \end{gathered}$$

Since, $X$ is at rest so the energy released $Q$ is 

$Q=\left(m_x{c}^2-m_y{c}^2-m_y{c}^2\right)=K_y+K_y$

The $Q$ value i.e. energy released is the rest energy of $X$ minus rest energy of $Y$ and $y$

When binding energy of products is more than binding energy of parent nucleus, then energy is released.