What is the formula for Mass defect?

Mass defect is the difference between the actual mass of nucleus and sum of masses of constituent nucleons.

The formula for Mass defect is given as,
m = [Z m_p + (A – Z)m_n] – M

M = mass of nucleus
A = mas number                           
m_p = mass of proton
Z = atomic number                              
(A – Z) = number of neutron
m_n = mass of neutron