The short answer
Separate gas supply, distribution charges and taxes. Check whether the usage and quoted price are in therms, Ccf or another unit before multiplying them.
The decision this guide helps you make
A supplier's dollars-per-therm price and a utility's fixed monthly delivery charge describe different things. Both can appear on the same bill.
Evidence to gather before deciding
Gather billed therms, meter read type, billing days, supply price, customer charge and gas distribution utility. Check the conversion printed on a bill using volume units.
The detail that is easy to miss
Compare winter and shoulder-season periods separately. A heating-heavy account can use little gas in summer while still paying fixed distribution charges.
Convert volume to billed energy once
Decision case · figures, where used, are hypothetical
An illustrative 1,000 Ccf multiplied by a 1.03 therms-per-Ccf factor equals 1,030 therms. At $0.60/therm, commodity cost is $618. Use the bill's actual conversion rather than treating this example factor as universal.
What would make this decision ready?
Mark estimated readings before comparing months. A later actual reading can create a reconciliation that resembles a price spike. Check quantity, days, conversion and price before assigning the increase to weather or the supplier.
Keep units consistent
A therm measures heat energy; a gas bill may also display a volume measurement and a conversion factor. Quote units must match the billed usage before calculating cost. The commodity price, monthly supplier fee, utility distribution charge and tax are separate components. If a quote uses a wholesale reference or a different energy unit, ask for an explicit conversion and the full delivered pricing formula rather than comparing the raw numbers.
Distinguish choice from transportation
The ICC describes small-customer choice programs in Nicor Gas, Peoples Gas and North Shore Gas territories. Ameren publishes a separate business gas transportation pathway. Transportation can involve supplier nominations, balancing, storage or other obligations beyond a simple commodity rate. Eligibility and timing follow the utility and account. Do not infer gas service options from your electric utility or treat every Illinois business as enrolled in the same program.
Stress-test winter exposure
Build a monthly usage profile rather than multiplying a mild month’s bill by twelve. Compare a base month, higher consumption at the same price, and higher consumption with a higher variable price. Fixed supply can reduce commodity price uncertainty while leaving weather-driven consumption uncertain. Document whether each price includes basis, transportation-related tasks and fees; missing inclusions can be larger than the difference between two advertised commodity prices.
An example gas budget
Illustrative inputs: 1,200 therms at $0.60 per therm and a $20 monthly supplier fee model to $740 for supply. If consumption rises 25%, the same price and fee model to $920. If only the commodity price rises 25%, the result is also $920 for this example, but both changes together would be $1,145. These are arithmetic scenarios, not quotes or predictions. Utility distribution charges and taxes still need a separate budget.
| 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.
Natural gas budget and stress-test calculator ↗
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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.