Illinois Price to Compare: Utility Supply vs ARES

The Illinois electricity Price to Compare is a starting benchmark for eligible customers considering an alternative retail electric supplier, commonly abbreviated ARES. It is not a promise that every account can take the same utility product, and it is not always an all-in supply number that can be compared to a supplier's headline price without adjustment.

Start with the Illinois Power Agency's electricity supply rate page, which links current ComEd and Ameren Illinois resources and directs customers to Illinois shopping information. Then confirm the account's service class and bill components.

When utility supply can be the better decision

Utility supply may be preferable when:

the applicable benchmark is below fully loaded retail offers;
a business values flexibility and the utility option does not create the same long commitment;
the available ARES contracts shift material, uncapped costs to the customer;
usage is uncertain and supplier volume-tolerance language is punitive;
the business lacks enough data to evaluate an indexed or structured product;
credit, deposit, or collateral terms erase the apparent price advantage.

“Doing nothing” is still a procurement decision. It should be documented with the same rigor as signing a supplier contract.

When an ARES offer can be better

A retail offer may be preferable when its total expected cost, budget behavior, and contract terms are better for the account. A business may value a defined fixed period even if the expected base-case cost is not the absolute minimum. Another account may prefer controlled index exposure because it can shift load or tolerate volatility.

The key is to compare equivalent scopes.

Comparison item	Utility benchmark	ARES offer
Effective dates	Exact rate period	Contract start and end
Energy	Included components	Fixed, index, or block structure
Capacity	Identify treatment	Included or passed through
Transmission	Identify treatment	Included or passed through
Losses/ancillaries	Identify treatment	Included or passed through
Monthly fees	Include	Include
Adjustments	Model separately	Identify formulas and caps
Exit/renewal	Utility rules	Contract notice and termination terms

The comparison calculation

Use 12 months of actual usage, or a longer period when operations are seasonal. For each month:

benchmark cost = applicable benchmark components × eligible usage + fixed fees + modeled adjustments

ARES cost = contract energy charge + capacity + transmission + losses + fees + modeled pass-throughs

Do not multiply a one-month utility benchmark by annual usage if the benchmark changes seasonally or at known effective dates. Do not compare a supplier price for a future delivery period with an old utility rate as though both were simultaneously available.

Add uncertainty, not false precision

Every comparison has uncertainty. Label inputs as:

known: executed tariff, actual historical load, stated fixed fee;
quoted: offer valid until a specific date;
estimated: future capacity, transmission, or usage;
unknown: uncapped change-in-law or discretionary cost.

Then show a base, low, and high case. If an unknown item can materially change the decision, request written clarification or reject the offer.

Contract questions before switching

Is the price fixed at the meter or subject to pass-throughs?
How are capacity and transmission determined and reset?
What happens if annual volume changes?
Does a material-change clause allow repricing?
What notice is required to avoid automatic renewal?
What happens at expiration if no replacement contract is signed?
Are taxes, renewable obligations, line losses, and ancillary charges included?
Is the supplier properly authorized? Check the Illinois Commerce Commission Office of Retail Market Development and relevant utility lists.

A defensible recommendation sentence

Instead of “Supplier A saves 18%,” write: “For the stated delivery period and modeled usage, Supplier A's fully loaded base case is lower than the applicable utility-supply benchmark by $X; the result depends on the listed capacity, transmission, and usage assumptions and is not guaranteed.”

That language exposes what can change and prevents a supply-only estimate from being represented as whole-bill savings.

Reading the benchmark without over-reading it

The published price to compare is a snapshot tied to a specific utility, service class, and effective period. Two mistakes recur. The first is treating one posted number as if it applied to every account on the utility. Service class, delivery voltage, and how supply-related components are grouped all change what "the" benchmark actually is for a given meter, so a figure quoted for one class is not automatically the figure for another. The second mistake is comparing a benchmark that will reset at a known effective date against a supplier quote for a delivery period that does not overlap it. If the benchmark you copied expires in a few months but the supplier term runs a year, the two prices never existed at the same time and should not be lined up as if they did.

Remember the split in Illinois: an eligible commercial customer either takes utility default supply procured through the Illinois Power Agency or signs with an ARES. The delivery utility — ComEd in northern Illinois or Ameren in central and southern Illinois — always delivers the power, maintains the wires and meter, and handles outages regardless of which supplier is chosen. Only the supply portion of the bill moves. A comparison that quietly folds fixed customer charges or delivery-related demand charges into a "savings" figure overstates the effect of the supply decision. Keep delivery out of the supply comparison entirely; it is the same either way. For how the delivery side works on its own, see the commercial demand charges and commercial utility bill review overviews.

Common mistakes when "doing nothing" wins

Assuming default supply is automatically the cheapest option because it is regulated. It is a published benchmark, not a guaranteed floor, and it can move at the next IPA procurement cycle.
Failing to document the decision to stay. An undocumented "no decision" is hard to defend at the next renewal, and it leaves no record of the assumptions that made staying reasonable.
Overlooking capacity and transmission treatment, which can differ between default supply and a retail offer even when the headline energy price looks similar.
Letting a quote "valid until" date lapse and then assuming the number still holds. A stale quote is not a live option.

Frequently asked questions

Is the price to compare the same for every business on ComEd or Ameren? No. It depends on service class and how supply components are grouped for that class. Confirm the applicable figure from the IPA and the utility for the specific account rather than reusing a residential number or a figure meant for a different class.

Does switching to an ARES change who restores power in an outage? No. The delivery utility still delivers energy, maintains the wires, and responds to outages regardless of who supplies the commodity. The supplier affects only the supply portion of the bill.

Can I just multiply this month's benchmark by my annual usage? Only if the benchmark does not change over the period. If it resets seasonally or at a known effective date, model each period separately and match the supplier quote to the same delivery window.

Where do I confirm a supplier is authorized to serve my account? Check the Illinois Commerce Commission Office of Retail Market Development and the utility's own list of authorized suppliers before signing.

Sources

Illinois Power Agency — electricity supply rates
Illinois Commerce Commission — Office of Retail Market Development
Related guides: compare offers apples to apples, how PJM capacity prices affect Illinois business bills, and the commercial electricity and commercial energy procurement overviews.

Source check date: July 19, 2026. Utility rates and supplier offers are time-sensitive.