  We show that calculation of a final fermion polarization (for a pure initial
state) is equivalent to the problem of looking for complete polarization axis
of bispinor. This gives the method for calculation of polarization applicable
both for final and intermediate state fermions. We suggest to use fermion
propagator (bare or dressed) in form of spectral representation, which gives
the orthogonal off-shell energy projectors. This representation leads to
covariant separation of particle and antiparticle contributions and gives a
natural definition for polarization of intermediate state fermion. The most
evident application is related with consistent description of $t$-quark
polarization.
