What we found

On six real ComEd commercial bills, the demand measured by each building's own meter equaled the demand ComEd billed, within 0.004 kilowatts.

The demand charge recomputed from ComEd's published rate matched each bill within ComEd's own rounding, and to the cent on the 2026 restructured bill.

On two buildings, the highest reading of the whole billing period fell outside the 9 AM to 6 PM on-peak window and was never billed. The demand charge is a rule about a window, not the building's physical maximum.

One bill did not reconcile because its interval data belonged to a different building. Phantom Grid declined to reconcile it rather than force a match.

Every bill, side by side

Site	Delivery class	Meters	Season	Measured kW	Billed kW	Difference	Bill demand charge	Result
A	Small Load (under 100 kW)	2	summer	40.91	40.91	0.00	$596.88	Matches the bill
B	Medium Load (100 to 400 kW)^*	1	early fall	91.944	91.94	+0.004	$1,374.50	Matches the bill
C	Medium Load (100 to 400 kW)	4	mid-summer	242.568	242.57	-0.002	$3,619.14	Matches the bill
D	Small Load (under 100 kW)	1	fall	22.92	22.92	0.00	$334.40	Matches the bill
E	Small Load (under 100 kW)	1	spring2026 format	46.20	46.20	0.00	$597.37	Matches to the cent
F	Small Load (under 100 kW)	1	fall	22.50	22.50	0.00	$328.28	Matches the bill

6 real ComEd commercial bills, reconciled against each building's own 30-minute interval data. Measured demand is the highest total across the building's meters during on-peak hours (9 AM to 6 PM, weekdays). No customer names, addresses, or account numbers.

* ComEd sets a site's delivery class on its trailing-twelve-month peak, not the billing month's. A site drawing under 100 kW this month can still be billed on the 100 to 400 kW class if it crossed 100 kW earlier in the year.

The window, again. On Site B a reading at 7:00 PM, after the 6 PM close, was the true high point of the whole billing period and carried no demand charge, while a lower on-peak reading set the bill. This is how the tariff is written, not a billing error.

Demand Charges

ComEd Demand Charges, Reconciled to the Meter

Name: ComEd commercial demand charges reconciled to interval data (2025 to 2026)
Creator: Phantom Grid
License: https://creativecommons.org/licenses/by/4.0/

Six real ComEd commercial demand charges, each reconciled against the site's own interval data. The measured on-peak demand equals the billed demand exactly, and the charge matches within ComEd's own rounding. Plus the one bill we refused to reconcile.

UPDATED JUL 24 2026

The exhibit above is not a projection or a model. Every row is a real ComEd commercial bill set beside the building's own 30-minute interval data, with the Distribution Facilities Charge (the demand charge, on the delivery side of the bill) recomputed from the tariff and checked against what the bill actually charged.

Why is this a reconciliation and not an estimate?

A reconciliation starts from the bill you were actually charged and proves, or fails to prove, that the meter data accounts for it. A calculator does the opposite: it multiplies a number you type in by a rate. The bill shows you only the result of the demand charge, never the single half hour that set it, nor whether that half hour fell inside the on-peak window. Putting the bill and the interval data back together is what makes the charge legible.

Why did we refuse to reconcile one bill?

Because its interval data did not belong to it. The file was a copy of a different, larger building's export, so the meter data and the bill described two different places. We could have forced a number. Instead the instrument returned "this does not reconcile." An engine that always hands back a confident answer is not honest, only confident. The ability to say no is what makes the other six results worth anything.

What we publish, and what we keep

We publish results: the demand each building's own meter measured, the demand ComEd billed, the bill's own charge, and the structural findings about the on-peak window. The rates and the on-peak rule are ComEd's, filed and public (ComEd Ill. C.C. No. 10, Rider RDS, and ICC Docket 24-0378), so you can check every result against the tariff yourself. What we keep is the engine that reproduces a bill to the last cent. The results are yours to verify. The method that gets there is ours.

Reconcile your own bill

You can run the same reconciliation on your own ComEd bill, to the cent, with the free demand charge tool. We do not sell energy and we take no commission. If you want this same reconciliation written up for one of your own buildings, that is the $500 verification.

What does "reconciled" mean here?

That the measured demand from the site's interval data equals the demand ComEd billed, and the charge recomputed from the tariff matches the bill. On these six sites the demand matches exactly and the charge matches within ComEd's own per-line-item rounding; on the 2026 restructured bill it matches to the cent.

Are these real bills?

Yes. Every row is a real ComEd commercial account, anonymized: no names, addresses, or account numbers. The figures are the actual billed demand and the actual Distribution Facilities Charge.

Why did one bill not reconcile?

Its interval file did not match its bill: the data was a copy of a different, larger site's export. Rather than manufacture a match, the instrument declined to reconcile. A refusal is a valid result, not a failure.

Can a demand charge be set by an interval I never think about?

Often, yes. On two of these sites the highest reading of the period fell outside the 9 AM to 6 PM on-peak window and was never billed, while a lower on-peak interval set the charge. The demand charge is a rule about a specific window, not the site's physical maximum.