Market-wide Half-Hourly Settlement: What It Means for SME Electricity Bills and Contracts

Market-wide Half-Hourly Settlement (MHHS) is the biggest rewiring of electricity settlement in a generation, and it is well past the discussion stage. About a third of Britain's metering systems are already settled half-hourly, and every remaining meter has to follow by spring 2027. For brokers and TPIs, the industry architecture matters far less than two questions: what changes on an SME's bill, and what to check in a contract signed this year. A third question is arriving with the data itself, because granular consumption records are now landing on sites that never had them.

Where the programme stands

Ofgem is the programme sponsor. Elexon is responsible for delivery, having taken on the Senior Responsible Owner and Implementation Manager roles. The design was signed off in 2022, followed by an extended testing period, central systems readiness in September 2025, and the start of live migration on 22 October 2025 (Elexon).

By mid-2026, more than 11.3 million meter points had been migrated, with two suppliers past the three-quarter mark of their own portfolios (Elexon). The total job is around 33 million MPANs. Once complete, Elexon expects to process up to 500 billion half-hourly readings a year, and settlement runs will finalise in about four months rather than the 14 months the old process took.

The dates that matter

These are the milestones worth writing into your own planning:

• 22 October 2025: migration begins, supplier by supplier, in waves.
• 28 October 2026 (Milestone 14): every supplier must be qualified and able to operate meters under the new Target Operating Model. Around this point Elexon expects to have accepted roughly 80 per cent of meters and to begin publishing aggregated data in the Smart Data Repository (Elexon).
• 7 May 2027 (Milestone 15): end of the migration window. All MPANs must be on the new arrangements.
• Early July 2027: cutover to the shortened settlement timetable, completing implementation.

Those dates come from the replanned timetable Ofgem approved through the programme's change control process, which moved the migration end date from October 2026 to May 2027 and the settlement cutover from December 2026 to July 2027. The current plan and milestone register are published by the MHHS Programme, and Ofgem's earlier replan decisions sit on its decisions pages.

A sharper edge now sits behind the final deadline. Ofgem has approved BSC modification P487, an Elexon incentive under which suppliers that fail to migrate their remaining meter points by 7 May 2027 face restrictions on taking on new customers (Ofgem). If you place volume with smaller or specialist suppliers, ask about their migration position directly. A supplier under acquisition restrictions cannot quote.

What actually changes on an SME bill

Start with the reassurance, because it is the question most business owners ask first. MHHS is a settlement reform, not a new levy. It adds no line to the bill and changes no agreed price or term mid-contract. Several suppliers have published exactly that position for their business customers, and the migration of an MPAN should be invisible on the day it happens.

What changes is the information underneath the price. Historically, most non-half-hourly SME sites were settled against a profile class: an industry-average assumption about when a small shop or office uses electricity. Under MHHS, sites with smart or advanced meters are settled on their own half-hourly consumption. Sites still on traditional meters are settled using a central load shaping service instead of the old profiles, so the accuracy gap between metering types becomes more visible.

The consequences show up over time rather than overnight:

• Shape-based pricing. Suppliers carry imbalance risk against actual half-hourly volumes, so a site with a favourable shape (daytime-heavy with onsite solar, or a business that can shift load away from peak) becomes cheaper to serve than the profile average. Expect wholesale risk premia to differentiate more between similar-sized sites.
• More time-of-use products. Static three-rate and day/night structures give way to genuine peak, off-peak and weekend pricing, plus limited-window flexibility offers for sites with storage or controllable load. These reward businesses that can move consumption. They penalise those who sign them and change nothing.
• Fewer estimate disputes. Settlement based on actual readings should reduce reconciliation surprises and the retrospective adjustments that have historically appeared months after a contract ended.
• Network charge classification. Distribution charges depend on how a meter is measured and settled, and DNO charging categories have been remapped for the new arrangements under DCUSA. When a site migrates, check the charging category shown on the invoice against the relevant DNO's use of system charging statement before assuming continuity. Any change in category, capacity charging or time band structure needs to be reflected in the pass-through element of a quote.

Ofgem's original business case put net consumer benefits at £1.6 billion to £4.5 billion between 2021 and 2045, largely from better price signals and reduced need for peak generation (Ofgem's MHHS decision and full business case). Those benefits arrive through customer behaviour and supplier competition, not automatically.

Contracts: what to read before signing

Contracts written across 2026 and 2027 straddle the migration, so the wording matters more than usual. Four things to check:

• Change of law and industry change clauses. Some suppliers reserve the right to pass through costs arising from settlement reform or from a change in a site's measurement class. Get that scoped tightly, ideally limited to genuine third-party charge changes rather than the supplier's own compliance costs.
• Volume tolerance. Half-hourly settlement makes forecast error more visible, and some contracts tighten tolerance bands or add shape-based adjustments. For a seasonal business, an aggressive tolerance band is a live cost.
• Data rights. Confirm the customer's right to receive their own half-hourly data in a usable format and to nominate you to receive it, for the whole contract term and after it ends. Non-domestic customers can generally have granular data collected, but the practical route to it varies by supplier and meter type, and consent records still need to be clean.
• Metering. Traditional meters are supported by MHHS but settled on modelled shapes, which usually means a worse deal than a site with real data. If an SME has a legacy meter, an upgrade to a smart or advanced meter is the single highest-value action before renewal.

What brokers should do with the new data

Half-hourly data changes the broker's job from price comparison to load analysis. Practical steps:

• Build a standing request into your onboarding pack: 12 months of half-hourly data per MPAN, plus the current charging category and any capacity figure.
• Profile each site once and keep it. Record the peak-window share, the weekend and overnight baseload, and the top 20 half-hours of the year. Baseload that persists when the premises are closed is usually the fastest saving you will find.
• Model at least two offers on the customer's actual shape rather than an annual quantity, so a time-of-use tariff can be compared honestly against a flat rate.
• Where a customer holds storage, EVs, refrigeration or heating that can shift, quantify the movable kWh before discussing flexibility or export offers.
• Ask every supplier on your panel for their migration completion status and wave, and note the P487 risk for any that are behind.
• Diarise reviews for autumn 2026 and spring 2027 so you can check invoices immediately after each portfolio migrates. Look at charging category, unit band allocation and any estimated periods.

Businesses that treat MHHS as an administrative change will end up paying the average. Those that examine their own half-hourly shape, cut overnight waste and price their peak honestly will pay less, and most will need help doing that analysis. For tracking slippage, Elexon's programme pages and the Balancing and Settlement Code MHHS hub are the reliable sources; broader smart metering policy sits with DESNZ and is a separate matter.