Demand Charge Calculator

How to use the demand charge calculator

A commercial electric bill is really two bills stacked together, and this tool splits them out so you can see each one. You enter your peak demand in kilowatts, the demand rate your utility charges per kW, your total monthly usage in kilowatt-hours, and the energy rate per kWh, and you get back the total bill, the demand charge, the energy charge, and the share of the bill the demand charge alone accounts for.

Every field is pre-filled with a representative example — a 10 kW peak at $15 per kW, and 3,000 kWh at 12 cents per kWh — so you can watch the tool work before swapping in the numbers off your own statement. Nothing here is a bill prediction; it is an arithmetic breakdown of a two-part tariff.

Start with the peak demand, because it is the input most people misunderstand. This is your highest sustained power draw for the month, measured in kilowatts, not the energy you used over time. Utilities almost always read it as the single highest 15-minute interval in the billing period — the worst quarter-hour, not an average — so it captures the exact moment your loads stacked up the most.

That is why a bakery firing every oven at once at five in the morning can carry a demand charge out of all proportion to its consumption. The default is 10 kW. If you do not know yours, it is printed on the bill, usually labelled peak demand, billing demand, or simply kW.

Next, the demand rate: the dollars-per-kilowatt your utility bills against that peak. Use your own tariff, because the spread is enormous. The National Renewable Energy Laboratory assembled demand charge rates from more than 10,000 US commercial and industrial tariffs in its Utility Rate Database work and found them ranging from under $5 per kW to over $50 per kW depending on territory, customer class and building type.

Roughly $15 per kW is the level at which peak-shaving battery storage starts to look economic; the $15 used here is an illustrative middle of that range, not a national figure. Then enter your monthly kWh and the energy rate per kWh from the same statement; the 12 cents used here is likewise illustrative, and the Energy Information Administration reported a US commercial average of 13.54 cents per kWh in May 2026.

Should I shave the peak or trim the usage?

The formula, worked line by line

A commercial bill adds two independent charges. One bills the energy you used over the whole month; the other bills the single hardest moment of power you drew. Compute each on its own terms and add them — that sum is the total, and the demand piece divided by the total is the demand share.

The two halves have different units for a reason: kilowatts are a rate of use, kilowatt-hours are an accumulated quantity, and a tariff that only charged for the second would leave the utility to size wires, transformers and generation for the first without being paid for it.

That is the whole logic of a demand charge. The grid serving you has to be built for your worst moment, not your average one, so the network cost is recovered against the peak. It is also why the charge is so unforgiving of spikes: an average would let a brief surge disappear into the rest of the month, and a peak reading refuses to.

Residential customers rarely see this structure at all, which is why the concept surprises people the first time they take on a commercial meter.

demand charge = peak kW × demand rate
energy charge = monthly kWh × energy rate
total = demand charge + energy charge
demand share = demand charge ÷ total × 100

The demand charge is billed on your highest sustained draw, which utilities typically read as the peak 15-minute interval in the month. A single brief spike — a compressor, an oven and a chiller all starting within the same quarter-hour — can therefore set the demand charge for the entire month even though it lasted fifteen minutes out of roughly 2,880 such intervals.

That is why two businesses using identical kWh can pay very different bills, and it is why the fix is scheduling rather than conservation. Peak shaving means not running big loads simultaneously; load shifting means staggering or time-shifting heavy equipment, or covering the surge from batteries.

Questions people ask