Off-system sales margin sharing on your bill is a credit that returns to you a share of the profit your utility earns when it sells surplus electricity on the wholesale market. Because your monthly payments helped fund the power plants, regulators require that most of that extra profit flow back to customers rather than stay with shareholders. The credit usually arrives through the same fuel adjustment line item you already see each month.
Where the Profit Comes From
Your utility’s first job is serving its “native load,” meaning the homes and businesses in its service territory. Generating plants rarely produce exactly that amount at any given moment. Mild weather, a neighboring utility’s maintenance schedule, and built-in reserve capacity all leave the utility with more electricity than local customers need at times.
Instead of letting that capacity sit idle, the utility sells the surplus to other utilities, power marketers, or regional grid operators. The industry calls these wholesale transactions off-system sales, and they fall under the Federal Energy Regulatory Commission’s authority over interstate electricity sales.1Office of the Law Revision Counsel. 16 USC Chapter 12 – Federal Regulation and Development of Power
One rule shapes everything that follows: serving native load always comes first. FERC Order No. 890 lets transmission providers reserve capacity for native load growth and gives native load higher curtailment priority than other grid uses.2Federal Energy Regulatory Commission. Order No. 890 – Preventing Undue Discrimination and Preference in Transmission Service If capacity is tight, the off-system sale doesn’t happen, and there’s no margin to share.
How the Credit Is Calculated
The “margin” is what’s left after the utility subtracts the variable costs of making the extra power from the wholesale revenue it collected. Variable costs are mainly fuel (coal, natural gas, nuclear fuel) and the operations and maintenance expenses that go up when a generating unit ramps output.
Fixed costs are deliberately left out. Plant construction debt, administrative salaries, and routine maintenance exist whether or not the utility makes any wholesale sales, and customers are already paying for them through base rates. Including them in the margin calculation would let the utility recover those costs twice.
So if a utility earns $7.8 million in wholesale revenue in a month and incurs $4.2 million in variable costs, the shareable margin is about $3.6 million. That is the figure the regulatory formula splits.
The Customer Share
Regulators don’t let utilities keep all of the margin, and they don’t hand all of it to customers either. The split is set to reward the utility for actively hunting profitable wholesale deals while making sure the public, which funded the plants, gets the larger share.
The most common structure gives 75% of the margin to customers and 25% to shareholders. Some jurisdictions use more customer-favorable splits like 90/10. Tiered structures also exist: a regulator might send the first $1 million in annual off-system sales profits entirely to customers, with anything above that threshold split 75/25.
Under a 75% customer allocation, the $3.6 million margin above would produce roughly $2.7 million in customer credits, with $900,000 going to shareholders. The shareholder cut matters because without it, utility management has little reason to staff a wholesale trading desk or optimize dispatch to catch off-system opportunities. The sharing percentage is the incentive.
How the Credit Reaches Your Bill
Margin credits flow through the fuel adjustment clause, which may be called a fuel cost recovery rider or something similar depending on your utility. That’s the line already on your bill that adjusts the base rate for changes in fuel and purchased power costs. The off-system sales credit gets folded in, often as a separate component that reduces the total fuel adjustment factor.
The credit is applied on a per-kilowatt-hour basis. The utility takes the customer share of the month’s margin and divides it by the total kilowatt-hours billed during that period. The result is a small per-kWh credit that applies proportionally: higher-use customers get a bigger dollar credit, but the rate reduction per unit of energy is the same for everyone.3eCFR. 18 CFR 35.14 – Fuel Cost and Purchased Economic Power Adjustment Clauses
Expect a lag. A margin earned in February might not appear on your bill until April, because the utility has to compile sales data, calculate the margin, and submit the figures to the state commission before applying the credit. Most utilities also run a monthly “true-up” to correct any over- or under-crediting from earlier periods, so even if a single month is slightly off, the numbers come out right over time.
Who Checks the Math
Regulators don’t simply trust what utilities report. Several layers of review stand behind the number on your bill.
Federal Reporting
FERC’s authority over wholesale electricity sales comes from the Federal Power Act. Section 205 requires wholesale rates to be “just and reasonable” and prohibits any “undue preference or advantage.”4Office of the Law Revision Counsel. 16 USC 824d – Rates and Charges; Schedules; Suspension of New Rates Major utilities also file annual financial reports on FERC Form No. 1, with wholesale revenues reported under Account 447 (Sales for Resale).5Federal Energy Regulatory Commission. FERC Form No. 1 – Annual Report of Major Electric Utilities, Licensees and Others Those filings create a paper trail regulators can match against the margin-sharing credits that reach your bill.
State Audits
State public service commissions set the sharing percentages, the formula, and the billing mechanism through rate case orders. Before a fuel adjustment hits bills, commission staff typically runs an arithmetic check on the utility’s computation statement. Many commissions also conduct semi-annual or annual audits of the utility’s fuel accounts to confirm that billed fuel cost adjustments match actual transactions, examining fuel procurement, purchased power, and interchange activity. If staff finds errors, the commission can order corrections in later billing periods.
Prudence Reviews
Beyond the arithmetic, regulators look at whether the utility’s trading decisions were prudent, judged by what was reasonable at the time rather than with hindsight. They compare off-system sales volumes, revenues, and costs against historical patterns and flag anomalies. A pattern of ignoring available wholesale opportunities, or selling at below-market prices, can lead to a finding that the utility failed to maximize the margins it should have shared with customers.
When Margin Sharing Doesn’t Apply to You
This framework belongs to traditionally regulated electricity markets, where a vertically integrated utility owns generation, transmission, and distribution, and recovers its costs through rates approved by a state commission. The bargain is explicit: the utility gets a guaranteed service area and the ability to recover prudent costs, and customers get oversight of its finances, including a share of wholesale profits.
In restructured or deregulated markets, the entity selling power at wholesale is typically a competitive generator, not a regulated utility drawing cost recovery from captive ratepayers. Those generators keep their profits and absorb their losses, because you aren’t funding their plants through regulated rates. If you live in a retail-choice state and buy electricity from a competitive supplier, off-system sales margin sharing isn’t part of your billing relationship.
Roughly two-thirds of states still have traditionally regulated electric utilities serving at least some customers. If your utility is a vertically integrated company whose rates are set by a state public service commission, some form of margin sharing likely applies to you, even if you’ve never spotted the line on your bill.