What Is a Capacity Charge on Your Electric Bill?

On a ComEd statement the line reads like leftover arithmetic homework: a Capacity Obligation of 2.51 kW, a Capacity Charge Rate of $8.34, a Capacity Charge of $20.94. Three numbers, no explanation of what the twenty-one dollars actually bought.

It bought a promise. Capacity charges pay power plants to exist and stay available on the worst afternoon of the year, the one where every air conditioner across a dozen states switches on at once. The electricity you actually consume is billed elsewhere, per kilowatt-hour. This is the standby fee. And for the 67 million people served by PJM Interconnection, the standby fee is where the data center boom has quietly come to rest.

PJM's most recent capacity auction, held in December 2025 for the 2027/2028 delivery year, cleared at $333.44 per megawatt-day, the maximum price the Federal Energy Regulatory Commission allows. It procured 134,479 megawatts of unforced capacity, at a total cost of $16.4 billion. Roughly $6.5 billion of that, according to the grid operator's own market monitor, traces to data centers.

What is a capacity charge on an electric bill?

Every regional grid needs supply it may never call on. Reserve generation sits idle for 8,700 hours a year so it can run for the other 60. Somebody has to pay those plants to stay in business anyway, and that somebody is you, through a capacity charge folded into your supply costs.

Where the charge appears depends on your rate plan. ComEd customers on hourly pricing see it broken out as its own line. Customers on the default fixed-price rate pay it too, buried inside the Electricity Supply Charge, which is why most people have never heard of it. The utility is not marking it up. As ComEd puts it in its own explanation of the line item: ComEd does not profit from the Capacity Charge; instead, ComEd simply passes the cost on to customers without markup.

How is the capacity charge calculated?

Two numbers multiplied together. Your Capacity Obligation, measured in kilowatts, is an estimate of how much electricity you personally drew during the previous summer's highest-demand hours. Your Capacity Charge Rate is set by the wholesale market. Obligation times rate equals charge, and the result resets every June.

That timing matters more than most people realize. The bill you get in August 2026 is priced off how you behaved on the hottest afternoons of 2025. You are, in effect, being invoiced for last year's air conditioning habits.

Why did my capacity charge go up?

Because the auction that sets the rate has been clearing at its ceiling.

PJM runs a forward auction called the Reliability Pricing Model, buying capacity years before it is needed. The December auction cleared at the FERC-approved cap for the entire footprint, a 1.3% increase over the previous year, and still came up 6,623 MW short of the reliability requirement. It was the first auction in which the whole region, including areas outside the auction, fell short.

The demand side is where the story lives. PJM's forecast peak load for 2027/2028 came in roughly 5,250 MW above the prior forecast. Nearly 5,100 MW of that increase is attributable to data center demand.

"But this auction leaves no doubt that data centers' demand for electricity continues to far outstrip new supply, and the solution will require concerted action involving PJM, its stakeholders, state and federal partners, and the data center industry itself."

Stu Bresler, Executive Vice President for Market Services and Strategy, PJM

Monitoring Analytics, PJM's independent market monitor, put a number on it in January. Data center load accounted for $6.5 billion, or 40%, of the $16.4 billion in costs from the December auction, according to the monitor's analysis of the auction. About $6.2 billion of that relates to data centers that have not been built yet, but which could come online by the 2027/2028 delivery year. Across PJM's last three base auctions, forecast data center load above existing levels accounted for $21.3 billion, or 45%, of the $47.2 billion in cleared capacity costs.

The monitor's language was blunt: Data center load growth is the primary reason for recent and expected capacity market conditions, including total forecast load growth, the tight supply and demand balance, the significant shortfall in cleared capacity, and high prices.

One reason the number is not worse: a price cap negotiated between PJM and Pennsylvania Governor Josh Shapiro. Without it, the market monitor estimated, the December auction would have cost $9.9 billion, or 38%, more. Across the two auctions where the cap and floor applied, it held down capacity costs by $13.1 billion. That mechanism has now expired.

Can you lower your capacity charge?

Partly, and only if your utility calculates an individual obligation rather than a flat pass-through. Because the obligation is measured against last summer's peak hours, what you do in July shows up on next June's bill. ComEd tells customers the window that moves the needle most is hot summer afternoons between 2 p.m. and 6 p.m.: precool the house overnight, delay the dryer and dishwasher, and enroll in day-ahead alerts that flag the hours the grid expects to strain.

This is genuinely different from ordinary energy conservation. Cutting a kilowatt-hour at 2 a.m. in November saves you the cost of that kilowatt-hour. Cutting a kilowatt-hour at 4 p.m. on the hottest day of August lowers a charge you will keep paying for the following twelve months. Our earlier look at why electric bills keep climbing as data centers expand traced the same mechanism from the wholesale market down to the mailbox, and PJM's emergency demand cuts during the July heat showed what the shortfall looks like when it stops being a forecast. The physical driver behind all of it, the reason a single facility can draw as much power as a small city, is laid out in our explainer on what AI data centers actually consume.

None of this is hidden. It is simply distributed: a few dollars a month across tens of millions of statements, standing in for tens of billions of dollars of promised generation. PJM closed bidding on its next capacity auction, for the 2028/2029 delivery year, on July 7, and will report the results on July 14 after 4 p.m. Eastern. It will be the first one run without the price cap. Whatever number comes out of it lands on bills a delivery year later, in a line item almost nobody reads.