BSUoS charges, explained.

What BSUoS pays for

Electricity has to be generated in the same instant it is used. Wholesale contracts get the country close, and then somebody closes the gap for every half hour of every day: paying a generator to turn up when demand comes in higher than the market expected, paying one to turn down when the wind blows harder than forecast, holding reserve, managing voltage and frequency, and working around network constraints. That is the balancing job, and Balancing Services Use of System is how it is paid for.

The costs it recovers are listed in Section 14 of the Connection and Use of System Code, the contractual framework for using the national transmission system. In plain terms they are:

• The Balancing Mechanism. What NESO pays generators and large users to change what they were going to do, in each half hour. The same accepted actions are what the imbalance price for that half hour is calculated from.
• Balancing services contracts. Reserve, response, inertia, voltage and restoration services bought ahead of time rather than in the moment, plus the cost of contracting for and developing them.
• Internal expenditure and returns. What it costs to run the system operator itself, and the return on its regulated asset value, both as defined in its licence.
• Adjustments. Corrections for prior years, manifest errors, special provisions, and costs under contracts awarded through the onshore tender process.

The scale is worth stating, because it explains why a charge nobody negotiates moves as much as it does. For the six months from April to September 2026, NESO forecast balancing costs of £1,285.2 million and internal costs of £400.0 million. After a negative recovery adjustment of £69.8 million and £6.1 million of other credits, the total to recover across those six months is £1,609.3 million.

Who pays it, and who does not

This is the part that has changed most, and the part most published explanations still get wrong. Until 1 April 2023, BSUoS was recovered from generation and demand together. Ofgem approved CUSC modification CMP308 on 25 April 2022, and from the start of the 2023/24 charging year the charge moved onto final demand only. Final demand means electricity consumed for any purpose other than generation or export onto the network.

You are not a party to the CUSC, so NESO never invoices you. It invoices your supplier for the demand your supplier settles, and your supplier recovers it from you. How visible that is depends entirely on the contract. On a pass-through contract BSUoS is billed at cost as a line of its own, or inside a combined non-commodity line. On a fully fixed contract it is inside the unit rate at a level the supplier guessed at, and priced a risk premium for, when the contract was signed.

How the tariff is set

Before April 2023 BSUoS changed every half hour and was only known after the event, which made it impossible to budget for and impossible to hedge. The Second BSUoS Task Force recommended fixing it. Ofgem approved CMP361, with the consequential CMP362, on 15 December 2022, and from 1 April 2023 the charge became an ex-ante fixed tariff: set in advance, the same for every settlement day in its period, and deliberately without a fund standing behind the tariff to smooth it. Two balances do exist, and they matter for one thing only, which is the mid-period reset described below.

Two further modifications, CMP408 and CMP415, were approved on 30 October 2024 and implemented on 1 April 2025. Together they shortened the notice period from nine months to three and lengthened the fixed price period from six months to twelve, which sounds contradictory until you see the shape it produces: NESO now sets a whole charging year at once, as two seasonal tariffs running April to September and October to March, giving a combined fifteen month framework. Fixed Tariffs 7 and 8 are the first pair published under it.

1. JuneInitial forecast

   A first view of both tariffs for the charging year starting the following April. Indicative only, and it has moved by December every year so far.

   →
2. SeptemberDraft tariffs

   The forecast rebuilt on later cost and volume data, published for industry to respond to. This is the committed month rather than the outturn: the first draft under the new timetable landed on 2 October 2025.

   →
3. By 31 DecemberFinal tariffs

   Both become the Fixed BSUoS Price. The second is known nine months before it applies.

   →
4. 1 April and 1 OctoberThe price steps

   The new tariff applies from the first settlement day of the period, with no transition across the boundary.

The tariff itself is the forecast total cost divided by the forecast volume it will be spread over. What lands on your invoice is that tariff applied to your volume, for each settlement day.

The number in the first term is produced by dividing forecast total BSUoS costs by the forecast of transmission connected and gross demand volume for the period. For April to September 2026 that is £1,609.3 million over a forecast 117.10 TWh, which gives £13.74 per MWh. For October to March it is £1,812.0 million over 145.04 TWh, or £12.49. Both were struck against forward price curves averaged over the first week of December 2025.

What it costs, worked through

Start with the case that has no complications: a billing period sitting wholly inside one fixed price period. The consumption below is an assumption, clearly labelled as one. The rate is not.

Consumption assumed, August 2026

250,000 kWh

Converted to MWh

250 MWh

Fixed Tariff 7, 1 April to 30 September 2026

£13.74 per MWh

250 × 13.74

£3,435.00

Now the case that catches people out, and the single most common way a BSUoS line is wrong: a period that crosses a tariff boundary. Take the same site on a monthly cycle that runs from 16 September to 15 October 2026.

Billing period assumed

16 Sep to 15 Oct 2026, 30 days

Consumption assumed, spread evenly

30,000 kWh

15 days at Fixed Tariff 7, 15 MWh × £13.74

£206.10

15 days at Fixed Tariff 8, 15 MWh × £12.49

£187.35

Total for the period

£393.45

Price the whole thirty thousand units at Fixed Tariff 7 and the line reads £412.20, an overcharge of £18.75 on one meter for one month. That is small enough to sit inside most tolerances and large enough to be worth several thousand pounds a year across a portfolio of a hundred meters, twice a year, every year.

Where it appears on your invoice

There is no standard line name. The same charge arrives under at least five different headings depending on the supplier, and one of them is not a heading at all.

If the line is bundled, you can ask your supplier in writing for the breakdown. That is worth doing before you need it rather than after, and for a business claiming network charge compensation it is not optional: obtaining the detail is explicitly the responsibility of the applicant, as the EII exemption guide sets out.

How to check it

BSUoS is the easiest large pass-through charge to verify, because there is exactly one rate in play and it is published. Five questions settle it, in this order.

• Does the period cross 1 April or 1 October? If it does, the line should be the sum of two calculations, not one. Look here first, because it invalidates everything after it.
• Is the rate the published one? Not the rate in the contract, and not last period. The Fixed BSUoS Price for the settlement days actually billed.
• Are the units consistent? NESO publishes in pounds per MWh and most suppliers bill in pence per kWh. Divide by ten, and check you have not divided twice.
• Is the volume the one the charge applies to? Gross demand volume at the boundary, not metered units. A line that matches your meter reading exactly may be the one that is wrong.
• Is this an original charge or a reconciliation? An amount for a period you have already paid for is normal. Price it against the tariff for the period reconciled, not the current one.

What is changing

The rate falls on 1 October 2026

Fixed Tariff 8 is £12.49 per MWh against Fixed Tariff 7 at £13.74, a fall of £1.25 per MWh or 9.1%. On a site consuming 250,000 kWh in a month that is £312.50 less. Both figures were published together on 29 December 2025, so a supplier has had nine months notice of the second and there is no excuse for an invoice that misses the step.

The pair before them ran the other way. Fixed Tariff 5 was £10.74 per MWh for April to September 2025 and Fixed Tariff 6 was £15.69 for the winter half, a rise of 46%. A charge that jumps 46% in one step and falls 9% in the next is not a number to carry forward from the budget you set last year, and the fixed tariff regime removed the volatility within a period without removing it between periods.

Tariffs 9 and 10 arrive by the end of December

The initial forecast for the 2027/28 pair was due in June 2026 and the draft in September 2026, with the final figures published by 31 December 2026. Until then nothing about April 2027 is fixed, and a forecast tariff is not a tariff.

Billing gross rather than net is under challenge

CMP453, raised on 30 April 2025, would bill BSUoS on a net basis at BSC Trading Units. Under gross billing a customer inside a trading unit pays BSUoS even where the net flow at the point of connection is an export, which is to say even where they are not using the system. The final modification report of 11 November 2025 asked for implementation on 1 April 2026 and for a decision by 30 November 2025. Neither happened: Ofgem lists CMP453 as a decision still pending, with a decision date of 30 September 2026. It matters most to sites with significant on-site generation.

Deep dives and edge cases

The main path above covers a BSUoS line on a current invoice. These are the cases that come up often enough to answer and not often enough to interrupt it.

Questions