  Charge transfer statistics of quantum particles is obtained by analysing the
time evolution of the many-body wave function. Exploiting properly chosen gauge
transformations, we construct the probabilities for transfers of a discrete
number of particles. Generally, the derived formula for counting statistics
differs from the one previously obtained by Levitov {\it et al.} (J. of Math.
Phys. {\bf 37}, 4845 (1996)). The two formulae agree only if the initial state
is prohibited from being a superposition of different charge states. Their
difference is illustrated for cases of a single particle and a tunnel junction,
and the role of charge coherence is demonstrated.
