Error analisys for the data generated via GEANT4 simukation

I am writing a simple program where I need to find the number of neutrons generated from various geometries when electron beam strikes it. Using G4MultiFunctionalDetector method I am able to find the total number of neutrons binned at various energies. I wanted to know how much will be the statistical error for the neutron count that I am getting in each run of few millions of histories. Should I manually find out by using error analysis formulae after running the program for 10 or more times? Or is there a better way to obtain statistical error through some command in GEANT4 itself?