Formal charge is a charge of an atom in a molecule. My formula to calculate formal charge is Formal Charge = number of valence electrons - (number of bonds + number of lone electrons). How do we find these numbers? Number of valence electrons is equal to the group number of an element on the periodic table. For example, Carbon, is in group four and thus has four valence electrons. Number of bonds is the number of bonds your atom is directly attached to. Number of lone electrons is the number electrons (dots) surrounding the atom.