The deflection \( \delta \) at the free end of a cantilever beam subjected to a concentrated load \( P \) at its mid-span can be calculated using the beam theory, which yields:
\[
\delta = \frac{PL^3}{24EI}
\]
where \( P \) is the load, \( L \) is the length of the beam, \( E \) is the modulus of elasticity, and \( I \) is the moment of inertia of the beam's cross-section.