Your ComEd Business Bill Jumped. Which of the Four Causes Was It?

The bill is materially higher than last month and nobody can tell you why. Before anyone sells you a solution, it is worth knowing which of four things happened, because they do not have the same answer and two of them are not problems at all.

You need two bills for this: the one that jumped and the one before it. Ten minutes.

Cause one: you used more energy

Compare the kilowatt hours on the two bills. If the jump is roughly proportional to the change in kilowatt hours, this is a usage story and the rest of the page does not apply to you.

Check the billing period length before concluding anything. A thirty-five day period against a twenty-eight day period is a twenty-five percent difference in energy on identical operations, and it happens routinely. Divide each bill's kilowatt hours by the number of days in its period and compare the daily averages instead of the totals. Half of the bill jumps that walk in the door are this, and this alone.

Cause two: a new peak reset your demand charge

Now compare the billed demand in kilowatts on the two bills. If the kilowatt hours barely moved but the kilowatts jumped, you did not use more power over the month. You used more power at once, for one interval, and the demand charge is billed on that single interval rather than on the month.

This is the cause that feels least fair and is the most likely to be actionable, because the event that caused it was short. Something started while something else was already running. A piece of equipment came back from repair. A hot week put every rooftop unit on at once at two in the afternoon.

Multiply the kilowatt difference by the dollars-per-kilowatt rate on the bill. That is what one interval cost you, and it is the number worth carrying into any conversation about what to do next.

Cause three: the supply price changed under you

Compare the supply dollars divided by kilowatt hours across the two bills. That is your effective supply rate, and if it moved while your usage did not, the change is on the supply side.

There are ordinary reasons for this. A fixed-price contract with a retail supplier reached the end of its term and rolled to a variable rate. The utility's default supply price reset on its scheduled cycle. A seasonal rate stepped up. None of these is an error, and all of them are things you can act on, but the action is a contract decision rather than an equipment decision.

Cause four: the two bills are not comparable

The least interesting cause and the one to rule out before spending money on any of the others.

An estimated read followed by an actual read produces a low bill and then a catch-up bill, and neither reflects a single month of operations. A rate class change, a meter exchange, or a correction to a prior period can land a true-up in a month it did not belong to. A bill that covers a different number of days than the one before it is not comparable at all until you normalise it.

Look for a period-length difference, an estimated-read marker, or a line describing a prior-period adjustment. If any of those is present, the jump may be an artifact of billing rather than a change in what your building did.

What you do with the answer

The four causes point in genuinely different directions. More energy points at equipment and schedules. A new peak points at what runs simultaneously, which is often a sequencing problem rather than an equipment problem. A supply price change points at your contract. A non-comparable pair points at nothing at all and saves you from acting on a phantom.

If it turns out to be a new peak, the bill has told you the size of the problem but not its cause. It preserves the maximum and discards the fourteen hundred readings that produced it, so it cannot tell you which afternoon it was or what was running. That question needs the interval record behind the bill, and it is worth knowing where the bill stops before you go looking.