DUoS 2027/28: pricing the draft tariff movements into SME renewals

Get the charging year right before you quote

There is a timing trap in this year's charging cycle, and it catches brokers every autumn. Distribution use of system charges for licensed suppliers are set under the Distribution Connection and Use of System Agreement, and distributors must give long notice of final charges for low voltage and high voltage sites. In practice, final 2027/28 tariffs were published back in December 2025, as Drax noted when it observed that the majority of DNOs issued 2027-28 DUoS tariffs in that month (Drax Insights).

So the papers landing on DNO websites this autumn, ahead of the 31 December statutory deadline, are the drafts for 2028/29. The 2027/28 numbers you need for a contract starting now are already final, subject only to limited revision. If a supplier tells you 2027/28 DUoS is "still indicative", ask which specific tariff and which code change is driving that, because for most CDCM sites it should not be.

Two caveats matter. Extra high voltage sites charged under the EDCM are site-specific and more prone to restatement. Published charges can also be re-issued where a code modification, a licence change or a correction bites, and Ofgem's annual iteration of allowed revenue feeds the next cycle rather than retrospectively rewriting a published year.

Where the movements show up

Read each statement in the same order every time, because the headline p/kWh tells you very little on its own.

• Red-band unit rate (p/kWh). The largest absolute mover in pence terms, and the one that decides whether a site's load shape is expensive. Red windows differ by region and by voltage, so check the time bands table rather than assuming 16:00 to 19:00 on weekdays.
• Fixed charge (p/day). Small in isolation, material across multi-site portfolios of shops and depots.
• Capacity charge (p/kVA/day). Since the Access significant code review reshaped charging from April 2023, agreed capacity does a lot of the revenue recovery work for half-hourly sites. A ten per cent move here hits a site with generous headroom harder than a red-band move does.
• Excess capacity charge (p/kVA/day). The DCP161 legacy rate, applied where recorded demand exceeds agreed capacity.

Compare like with like across years by rebuilding each tariff into a single p/kWh figure for the actual site, not by averaging the DNO's rates. A region with a modest red-band rise and a sharp capacity rise can still land a bigger bill increase on a light-load, high-capacity site than a region with the eye-catching red number.

Worked example: a contract straddling 1 April 2027

Take a typical half-hourly SME: 600,000 kWh a year, 250 kVA agreed capacity, red-band share of consumption at nine per cent, amber 35 per cent, green 56 per cent. The rates below are illustrative placeholders to show the method; substitute the published figures for your own DNO and tariff line.

• 2026/27: red 12.50p, amber 1.10p, green 0.30p, fixed 95p/day, capacity 3.20p/kVA/day
• 2027/28: red 14.10p (+12.8%), amber 1.18p (+7.3%), green 0.32p, fixed 104p/day (+9.5%), capacity 3.55p/kVA/day (+10.9%)

Annual DUoS at 2026/27 rates comes to £13,334, or 2.222 p/kWh. At 2027/28 rates it is £14,786, or 2.464 p/kWh, an increase of 10.9 per cent even though no single component moved by that much. Note how the weighted outcome sits below the red-band percentage: only nine per cent of the volume sits in the red band.

Now price a twelve-month contract running 1 October 2026 to 30 September 2027. That is 182 days on the old rates and 183 on the new. Blended cost is £14,062, or 2.344 p/kWh. Quote the site at the current-year rate and you are £727 short over the term, which is 0.122 p/kWh of margin gone.

To build the allowance, calculate the site-specific p/kWh for each charging year from the published statements, then weight by days either side of 1 April 2027. Add a buffer for volume shape drift, because a site whose red share creeps from nine to eleven per cent adds roughly 0.05 p/kWh at the 2027/28 red rate. For 2028/29 straddles, where the tariffs really are draft, widen that buffer: final CDCM charges have historically moved only modestly from draft, but capacity and excess rates can be revised more than unit rates.

Fixed or pass-through

For a single-site SME on a one-year deal that straddles 1 April 2027, fully fixed is usually the cleaner sell, because the 2027/28 numbers are already published and the risk you are pricing is volume shape, not tariff uncertainty. Charge the blended rate, keep the buffer modest, and the customer gets one number.

Pass-through earns its keep on contracts of 24 months or more that reach into 2028/29 and the start of the next distribution price control. It also suits sites actively changing their load shape or capacity, and portfolios spread across several DNO regions, where a single fixed uplift over-recovers in some places and under-recovers in others. Be honest with the client that pass-through also exposes them to changes in other network and policy costs, which sit outside DUoS and follow their own timetables at Ofgem.

Half-hourly checks that find the exposed sites

Pull twelve months of HH data from the supplier or from the data collector, and run three tests.

• Red-band share. Map each half hour to the DNO's published bands. Above roughly 12 per cent of annual volume in red, the site is unusually exposed to red-rate movements. In the example above, shifting a tenth of red consumption into green saves about £744 a year at 2027/28 rates.
• Capacity headroom. Take the maximum recorded kVA and compare with agreed capacity. Utilisation below about 60 per cent means the client is paying for capacity it does not use; at 3.55p/kVA/day, trimming 50 kVA saves £648 a year. Do not cut without checking seasonal peaks and any planned electrification.
• DCP161 exposure. Flag every half hour above agreed capacity. Excess capacity rates sit above the standard rate in most statements, so persistent small breaches often cost more than simply increasing agreed capacity. In the example, raising capacity from 250 to 275 kVA costs £324 a year.

Settlement-grade data quality matters here, particularly as sites migrate under market-wide half-hourly settlement; Elexon publishes the programme position.

Dates to diarise

• Autumn 2026: draft 2028/29 charging statements from each DNO, plus any revisions to published 2027/28 figures.
• 31 December 2026: statutory deadline for final 2028/29 charges.
• 31 January 2027: final TNUoS tariffs for 2027/28 from NESO, relevant if you quote network costs as a single bundled item.
• 1 April 2027: 2027/28 charges take effect.
• 1 April 2028: start of the next distribution price control, the point at which allowed revenues, and therefore tariff trajectories, reset.

Do this on your next five renewals

Rebuild each site's DUoS in p/kWh for both charging years using the published statements, weight by days either side of 1 April 2027, and show the client the blended figure alongside the current-year figure so the increase is visible rather than buried in a unit rate. Run the half-hourly checks next, and put any capacity change through the DNO before 1 April so the saving lands in the new charging year. Keep a dated one-page note on every quote file recording which numbers are final and which are draft.