Demand charges are calculated from the single highest average rate at which your facility drew power during any one measurement interval — usually 15 minutes — across the entire billing period, and you are billed per kilowatt on that one reading. Understanding how demand charges are calculated is the difference between managing a controllable cost and absorbing a number nobody in your building can explain.

This is written for plant managers, facility directors, COOs, and energy managers at Indiana manufacturers, hospitals, school systems, cold storage operations, and large commercial facilities. If your electric bill runs five figures or more every month, demand charges commonly exceed 50% of what you pay. That means one peak reading can drive the majority of your bill.

By the end of this, you'll know exactly how the calculation works, the five demand charge structures you're likely to find in your tariff, how ratchet provisions carry a summer peak into your winter bills, and the questions that expose a vendor proposal built on generic assumptions instead of your actual rate.

What Demand Charges Actually Are

Your utility bill has three components. Fixed charges are unavoidable and assessed for being connected to the grid. Energy charges are billed per kilowatt-hour based on total consumption over the month. Demand charges are billed per kilowatt based on the maximum rate at which you drew power at any single point during the billing period.

Most operators understand the energy charge intuitively. You use more, you pay more. Demand charges do not work that way, and that is where the confusion lives.

The distinction is between total and rate. Energy (kilowatt-hours, kWh) measures total consumption over time. Demand (kilowatts, kW) measures the rate of consumption at a given moment.

Here is the example from the episode. A central air conditioner rated at 3,500 watts running for eight hours draws 28 kilowatt-hours of energy. Now add a 4,000-watt water heater running at the same time for those same hours. Your combined demand at that moment is 7.5 kW. Run the water heater before the air conditioner kicks on instead, and your demand never exceeds 3.5 kW. Same total energy consumed, completely different demand reading, and a different all-in bill.

The gap between what you used and what you are billed for is where the demand charge lives.

How Demand Charges Are Calculated on Your Utility Bill

Most utilities measure demand on a 15-minute interval, though some use 5, 30, or 60-minute windows. Check your tariff. Your tariff is the rule of the game.

Whatever the interval, the highest average draw in any one of those windows becomes your billing demand for the entire month. One bad interval, on one day, can define your costs for a full 30 days. Nothing you do for the other 2,879 intervals in the month changes that number.

That single mechanic is why conservation programs aimed at total consumption often produce a smaller bill reduction than operators expect. Cutting kilowatt-hours across the month does not touch the demand line item unless it also flattens the peak.

The Five Demand Charge Structures You'll See in a Tariff

Max or non-coincident demand is charged on your highest draw at any point in the billing period, regardless of when the utility's own system peak occurs.

Time-of-use demand is charged on your highest draw within a specific defined on-peak window. Those windows vary by utility.

Flat demand applies a single rate per kilowatt to one demand reading.

Tiered demand applies different rates depending on whether your demand sits above or below a threshold.

Daily demand charges are billed per kilowatt per day across the billing period. This is a newer structure that is expected to become much more common.

Identify which one your facility is on before you evaluate any project, because the payback math changes completely between them.

Demand Ratchets: The Provision That Catches Operators Off Guard

A demand ratchet is a minimum billing floor. Your actual demand in a given month might be far lower than what you are billed for. The most common forms are a fixed kilowatt minimum and a minimum derived from applying a percentage to a referenced demand from a prior period.

Here is a real structure. A utility tariff sets a fixed minimum billing demand of 100 kW during winter months and states that your billing demand cannot be less than 70% of your highest metered demand from the prior summer. If your peak in August was 400 kW, your November billing demand is 280 kW — no matter what you actually drew in November.

A single summer startup event or equipment test can set your billing baseline for months. Audit your tariff for ratchet language. This is not hypothetical. For a full breakdown of how these provisions carry forward, read our guide to demand ratchets for Indiana commercial and industrial operators.

Ratchets and interval peaks are also one of the most common places billing errors and misapplications hide, which is why utility bill audits for Indiana C&I operators so often turn up recoverable money on the demand line.

Why Demand Charges Exist on Paper vs. How They Work in Real Life

Utilities and regulators will tell you demand charges recover the cost of building infrastructure sized to your maximum possible draw. Transformers, lines, and generation capacity have to be sized for your worst 15 minutes, not your average hour. On paper, the charge sends a price signal that rewards facilities for drawing power steadily.

In practice, there is a wide gap between the people who design rate structures and the people running production floors. The price signal only works if the customer can see it, understand it, and act on it. Most C&I customers get a monthly summary bill weeks after the peak was set, with no visibility into which interval caused it and no notification when they are approaching a new high.

The structure is designed to change behavior. The information flow makes that nearly impossible for most operators without their own interval data. That is a design failure, not an operator failure.

When Your Demand Charge Structure Works in Your Favor

Some facilities come out ahead under demand-based billing, and it is worth knowing whether yours is one of them:

• Your draw is steady and predictable. Continuous-process operations that run near a flat load, around the clock, spread their infrastructure cost across a lot of kilowatt-hours and typically pay a lower effective rate per unit than a spiky facility with the same monthly total.
• You control your startup sequence. If your largest motors, compressors, and process heat can be staggered by a maintenance or production scheduler, the lever is operational and costs nothing to pull.
• You're on a time-of-use demand structure and your production can run off-peak. A defined on-peak window is a target you can schedule around. A non-coincident max demand charge gives you no such window.
• You have interval data and someone who looks at it. Facilities that can see the peak forming can act before it sets.

When Demand Charges Quietly Wreck Your Budget and Lock You In

• Your tariff has a ratchet and nobody has read it. You can run a disciplined fall and winter and still pay on a peak from August.
• Your peak comes from short, non-production events. Equipment tests, simultaneous startups after an outage, or an unusual shift schedule can set a number that has nothing to do with how you normally run.
• Your loads genuinely cannot move. Some processes have no flexibility. If that is your situation, sequencing will not help you and you need to evaluate storage or rate structure changes rather than scheduling changes.
• You're forecasting your budget off kilowatt-hour trends. Reducing consumption alone will not fix a bill where demand charges are the majority of the cost.
• You signed a project that modeled generic assumptions. A storage or generation project sized against regional averages instead of your specific demand rate and interval window can miss the peak entirely and still produce a bill.

Vendor Pitches, Red Flags, and Questions That Smoke Out Bad Math

For facilities with the right load profile, battery energy storage for peak shaving can produce real paybacks. A vendor case study from Sunlith Energy describes a manufacturing facility with more than $50,000 per month in demand charges that installed a 5 MW / 10 MWh system and reported a 35% demand reduction with a four-year payback.

Treat vendor case studies as directional. The economics depend heavily on incentives, tariff structure, and whether the battery is also earning ancillary revenue. Our breakdown of battery energy storage system payback for C&I operatorswalks through what has to be verified before signing, and FERC Order 2222 and DER aggregation covers the wholesale revenue side of that stack.

One more thing worth knowing: solar does not reduce demand charges as efficiently as it reduces energy charges. Generation does not reliably coincide with your peak demand window, especially under time-of-use tariffs where on-peak periods run into the evening after solar output drops. Intermittency from passing clouds can create demand peaks rather than shave them. If a vendor is pitching solar as your demand charge solution, push back on that math.

Questions to put in front of any vendor:

• What is my measurement interval, and did your model use it or a generic 15-minute assumption?
• Which of the five demand structures am I on, and did you price my actual per-kW rate or a regional average?
• Does my tariff contain a ratchet, and how does your model handle a billing floor set by a prior-period peak?
• What happens to your projected savings if the system misses the monthly peak by one interval?
• Are you modeling demand reduction and energy reduction separately, or blended into one number?

What You Can Do This Week

1. Pull your last twelve bills and calculate what percentage of each is demand charges. If you have not run this number in the last 90 days, you are guessing at where your money goes.
2. Read your tariff sheet for ratchet and minimum billing demand language. Note the percentage, the reference period, and the seasonal months it applies to.
3. Find your measurement interval. Fifteen minutes is common but not universal, and the answer changes how you sequence.
4. Map your largest equipment startups against each other. Identify anything that comes online simultaneously and could be staggered by a scheduling change instead of a capital purchase.
5. Request interval data from your utility if you do not already have it. You cannot manage a peak you cannot see.

Load sequencing is the most accessible near-term lever. Do not run your largest loads simultaneously, stagger startups, and schedule discretionary loads outside the on-peak windows your tariff defines. These are operational decisions, not necessarily capital investments. If you want the full strategy set, start with demand charge peak shaving for Indiana C&I operators.

The Bottom Line on Demand Charges

Demand charges are not a line item you negotiate away. They are a structural reality written into your tariff. If you do not understand exactly how they are calculated — specifically the interval measurement window and any ratchet provisions tied to seasonal peaks — you are making capital decisions, operational decisions, and budget forecasts without the information you need.

Reducing kilowatt-hour consumption alone will not fix your bill if demand charges are driving the majority of your cost. The number that controls your outcome is your interval peak, and a ratchet provision can make a single bad day expensive for months afterward.

The trend among some utilities is toward more demand charge complexity: California utilities pushing more cost recovery into time-of-use demand, PG&E's Option S introducing daily demand charges, APS and Duke offering residential demand rates. It is uneven and contested at the regulatory level, but the direction is worth tracking in your service territory.

Frequently Asked Questions: How Demand Charges Are Calculated

Q: How are demand charges calculated on a commercial electric bill?
A: Your utility records the average rate at which you drew power in every measurement interval during the billing period, usually 15 minutes, and bills you per kilowatt on the single highest one. Total consumption has no effect on that number. One interval on one day sets the demand charge for the whole month.

Q: Why did my electric bill go up when I used less electricity?
A: You almost certainly set a higher peak demand even though your total kilowatt-hour consumption dropped. Starting several large loads at the same time for a few minutes raises billing demand without adding much energy. Pull the demand line item on both bills and compare the kW readings, not the kWh totals.

Q: What is a demand ratchet and how do I know if I have one?
A: A demand ratchet is a minimum billing floor that carries a past peak forward into later months, so you can be billed for demand you never used. The two common forms are a fixed kilowatt minimum and a percentage of a prior period's metered peak. The only way to know is to read your tariff sheet for ratchet or minimum billing demand language.

Q: Does solar reduce demand charges?
A: Solar reduces energy (kilowatt-hour) charges far more reliably than it reduces demand charges. Generation does not consistently line up with your peak demand window, especially under time-of-use tariffs where on-peak periods run into the evening, and passing clouds can create demand peaks instead of shaving them. If a vendor is selling solar as a demand charge fix, ask to see the interval-level math.

Q: What percentage of a commercial electric bill is demand charges?
A: For large commercial and industrial customers, demand charges commonly exceed 50% of the total bill. The share depends on your tariff and your load profile, so the reliable move is to pull your last twelve bills and calculate it for your own facility. If you have not run that number in the last 90 days, run it.

If this has you thinking about a project already in motion — storage, rate analysis, or just getting clear on what your bill is actually telling you — we built the TEG Energy Decision Blueprint for Indiana commercial and industrial operations spending five figures or more on electricity each month. We look at your bills, interval data, and any quotes or proformas on the table, then give you a written opinion on whether the project makes sense for your specific operation, whether the payback will materialize, and what risks the vendor has not surfaced. No obligation, and free to qualified Indiana operators.

For the foundational explainer on this topic, read our guide to demand charges for commercial and industrial facilities. If you're evaluating a rate structure change, start with time-of-use demand rates for Indiana C&I facilities.

Watch this Energy Answers episode on decoding demand charges on YouTube.

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