Formal Charge Calculator
Find the formal charge on an atom in a Lewis structure from its valence electrons, lone-pair electrons and number of bonds.
How it works
Formal charge = valence electrons − lone-pair electrons − (bonding electrons ÷ 2) · = V − lone − bonds
Formal charge is a bookkeeping tool that assigns each atom the electrons it would own if every bond were split evenly. An atom keeps all its lone-pair electrons plus half of every bonding pair — one electron per bond. Subtracting that count from the atom’s neutral valence-electron total gives the formal charge, and the sum of formal charges across a structure must equal the molecule or ion’s overall charge.
Worked example
For the doubly bonded oxygen in CO₂: valence electrons 6, two lone pairs = 4 non-bonding electrons, and 2 bonds. Formal charge = 6 − 4 − 2 = 0, so that oxygen is formally neutral.
Sources: Formal charge — Wikipedia
Frequently asked questions
How is formal charge different from oxidation state?
Formal charge splits every bond evenly between the two atoms, while oxidation state gives both bonding electrons to the more electronegative atom. They answer different questions and usually give different numbers.
Do I count lone pairs or electrons?
Enter electrons: each lone pair is 2 electrons. A structure with two lone pairs on the atom means 4 non-bonding electrons.
Why does formal charge matter?
The most stable Lewis structure is generally the one with formal charges closest to zero and any negative charge on the most electronegative atom. It helps you pick between competing resonance structures.
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This calculator is for educational purposes. Double-check important results before acting on them.