A commercial electricity bill is really several bills in one: energy you used, the wires that delivered it, the peak you demanded from the grid, and the taxes assessed on all of it. Each part is calculated differently, and each can carry its own errors.
Energy charges
The consumption line: kilowatt-hours used, multiplied by your contracted rate. This is the part your supply contract controls. The check worth running is whether the rate on the invoice matches the rate in the contract, including any tiers or time-of-use terms.
Delivery charges
The regulated utility's charges for moving power to your meter. These pass through regardless of which supplier you choose, and they change when the utility's tariffs change. Errors here usually come from the account being assigned to the wrong tariff class for how the facility actually operates.
Demand charges
Demand charges are billed on your highest usage interval in the period, measured in kilowatts, and they can be a large share of a commercial bill. A single unusual spike can set the demand figure for the month. Reviewing how demand is measured, and whether the billed peak matches the meter history, is one of the most common places an audit finds money.
Taxes and assessments
Sales tax and assessments apply differently by organization type and use. Some organizations qualify for exemptions they have never filed. When a bill has been running for years without review, tax treatment is a frequent source of recoverable cost.
Where to start
Line up one recent bill with the supply contract and check three things: the rate against the contract, the tariff class against the operation, and the billed demand against the meter history. That simple reconciliation is the core of what a bill audit does, at scale, across every line.