What is your real cost per kWh?

Start with one honest number

Every business already has a true price for its energy. It has just never worked it out.

Take the last bill. Find the total you were charged before VAT. Divide it by the number of units you used. That figure, in pence per kilowatt hour, is your all-in cost. It needs no further explanation and no second document. One bill gives a valid answer.

The reason to start here is that a tariff is almost impossible to judge by eye. Contracts run from a single rate plus a standing charge, through day-and-night bands, up to half-hourly pricing that changes through the day. Even the simplest of those hides a trade-off, because the standing charge and the unit rate move against each other, and nobody weighs that in their head. It is a little like a mobile data bundle. You accept the shape of the package without ever knowing whether it fits how you actually use the thing.

One number cuts through all of it. It answers the only question most businesses really want answered: am I okay, or is someone taking too much. The number does not say who. It makes the question askable, which is the point.

What the number captures

The blended figure is honest because it hides nothing. It folds the standing charge back into the per-unit cost, which is exactly where cost sits for a low-load site. It exposes the network and levy layers that an advertised unit rate quietly leaves out. And it is comparable across contract types in a way no single rate can be, because it is built from what actually happened rather than what was quoted.

It also has one blind spot worth naming. Averaging flattens the timing of your demand. A blended number treats a unit bought at 3am the same as one bought at the winter peak, so it cannot, on its own, show where a saving would come from. That is why the number is the opening, not the whole story. The headline is the average. The argument lives in the layers beneath it.

Should, and could

Anyone with twelve months of bills can compute their own number. What they cannot easily do is place it.

Two questions sit just past the arithmetic. What should the number be, measured against sites like yours? And what could it be, if you changed something? The first is a benchmark question, and it needs a comparison built from real sites rather than a national average banded only by size.

The second is where the number stops being a diagnosis and starts being something you can move.

The could is the interesting half. With solar and battery on site, the units you generate and use yourself are effectively free, so the blended cost of everything you consume falls, even when the price of the units you still buy from the grid does not. The number becomes a lever you flex, not just a reading you take. Both halves connect back to the questions of whether you are overpaying and whether your tariff matches how you actually use energy. The all-in number is what makes both of those legible in a single figure.

What moving the dial looks like

Take a site Vester monitors, a small commercial portfolio across several meters.

On today’s contracts, its all-in cost worked out at 26.1 p/kWh. That is the honest figure, everything charged over everything used. A switch to a day-ahead tariff brought it to roughly 23.0p. Adding a battery took it further, to 21.7 p/kWh. A cut of 4.4p, or 17%, in the true cost of every unit the business buys.

The tariff switch and the battery do different work. The switch lowers what the site pays the market for the units it still imports. The battery lets it buy when power is cheap and lean on stored energy when it is expensive, so fewer units are bought at the worst moments. Neither is visible on a unit rate. Both show up cleanly in the all-in number, which is why it is the natural measure for this kind of conversation. You measure the number, model where it could land, act, then watch that it stays down.

What you’re paying vs what you could buy it for

The all-in number tells you whether you are okay. The next question is sharper. Could the same power cost less?

To answer it honestly, compare like with like. Only ever set all-in against all-in, never all-in against an advertised unit rate. An advertised rate is a price for energy alone. Your all-in number carries the network charges, the levies and the standing charge as well. Put the two side by side and the all-in figure always looks worse, though nothing is actually worse. You are comparing two different things and calling it a contest.

So build the comparison properly. Take what a site is billed, all-in, and set it against what the same supply could be bought for, all-in, on a tariff better matched to how the site actually uses power. Both figures come from the site’s own data. Both already carry every layer, with realistic margin priced in. Now it is the same unit on both sides, and the gap between them means something.

On a small commercial portfolio Vester monitors, the gap is plain. They are billed at 26.1 p/kWh. The same units, on a better-matched day-ahead tariff, price at 23.0 p/kWh. That leaves at least 3.1 p/kWh, or £86,779 a year, on power they were always going to buy. The arithmetic closes: 23.0 plus 3.1 is 26.1.

That gap is not an accusation. It is a question. On units you cannot avoid buying, what is the difference for? No advertised unit rate would ever have shown it to you.

Simple, because it is understood

We have made this point before: to make something genuinely simple, you first have to understand it deeply. The all-in number is a small example of that. Behind one figure sit wholesale prices, network tariffs, policy levies and the shape of a building’s demand across a year. The work is in the understanding. What reaches the page is a single division anyone can run from a bill.

That simplicity is deliberate. A number you cannot explain is a number you cannot trust, and a business should always understand what it is being shown and why.

Where to go next

If you want to know whether your own figure is high, the honest test is a benchmark built from your real half-hourly data rather than from a quote. That is the same method behind checking whether you are overpaying, and you can walk through it step by step in how to benchmark.

To see your own all-in number, and what it could become, book a benchmark. You bring a recent bill. We bring the context.