The short answer
Start with account class, billing period and usage, then separate supply, delivery, taxes and adjustments. Read the units before interpreting an increase.
The decision this guide helps you make
Reconcile meter usage and days before comparing rates. Check whether supply is billed by the utility or separately by a supplier.
Evidence to gather before deciding
Record kWh, any billed kW, meter read status, supplier name, customer charge and adjustments on a simple worksheet.
The detail that is easy to miss
A bill can rise with unchanged rates when the billing period is longer. Daily energy use and comparable seasonal periods help separate consumption from pricing.
Bridge quantity and price changes
Decision case · figures, where used, are hypothetical
Usage moving from 8,000 to 10,000 kWh while price moves from 8 to 9 cents raises energy cost from $640 to $900. Extra use at the old rate explains $160; the price increase on current use explains $100.
What would make this decision ready?
Reconcile delivery, demand, taxes and adjustments separately. Check reading type and billing days. This arithmetic explains the increase, not whether weather, equipment or error caused the additional use.
Build a comparable cost basis
Start with one billing period and keep the account and usage constant. Multiply the offered cents per kWh by monthly kWh and divide by 100, then add the supplier fees and any separately priced components. Repeat for the other offer. If a component is unknown, label it unknown instead of silently entering zero. A quote that fixes energy but leaves capacity variable does not have the same risk as one that includes both. Expected cost and cost certainty are separate comparisons.
Read the agreement behind the price
A pricing schedule and the general terms work together. Check the delivery start, term, renewal language, customer obligations and provisions for changes in law or load. Identify whether a number is fixed for the whole term, reset at a stated interval or reconciled later. Obtain explanations in writing. Ask what happens if the business closes, moves, changes operating hours or replaces major equipment; do not assume the lease and supply agreement end together.
Separate supply from utility delivery
The utility continues to maintain the distribution system and handle outages. Supplier shopping does not eliminate regulated customer charges, every demand charge or taxes. Use the price applicable to your service class and product. Residential price-to-compare information can explain concepts, but it is not a commercial quote. If two consecutive bills differ, inspect billing days and consumption before attributing the full dollar difference to a supply rate.
A worked cost comparison
Illustrative inputs, not Illinois market offers: 25,000 kWh per month, offer A at 8.5 cents/kWh with no monthly fee, and offer B at 8.1 cents/kWh with a $35 monthly fee. A models to $2,125 and B to $2,060 for those supply components. The $65 monthly difference becomes $1,560 over 24 identical months. This excludes delivery, taxes, unentered pass-throughs and load changes. B reaches the same modeled cost as A at 8,750 kWh per month. Use your own data in the offer calculator.
| Record | Why it matters | How to verify |
|---|---|---|
| Account and scope | Keeps the decision tied to the right service and customer. | Use the current utility, meter and customer class; keep account identifiers private. |
| Period and units | Prevents comparisons across different months or measures. | Write down billing days and whether the amount is kWh, kW, therms or dollars. |
| Written terms | Distinguishes a claim from an obligation. | Save the full proposed agreement, tariff or program notice and its date. |
| Unknowns and exclusions | Shows what the estimate cannot establish. | List unresolved charges, eligibility and operating assumptions before deciding. |
Use a tool without sending your numbers
A calculator is useful for checking an assumption, not for confirming a tariff, incentive or legal interpretation. Enter only nonidentifying figures in the relevant worksheet. If you need a human review, describe the question and utility first; do not paste an account number or confidential document into the inquiry. Keep the model alongside the written terms so an apparently precise output is not mistaken for a complete quote.
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Sources & further checks
Primary references checked for this guide on October 15, 2026. Follow the source for current tariffs, eligibility and program terms; rates here are not live offers.