The way electricity is measured and settled in the UK is changing fundamentally. Market-wide Half Hourly Settlement - known as MHHS - is a multi-year programme that will require all electricity meters, for all customers, to settle on a half-hourly basis. Not just large commercial sites with advanced metering, but every business and household connected to the grid.

For organisations that already have half-hourly meters, MHHS changes the settlement infrastructure around them. For organisations still on non-half-hourly arrangements, MHHS may require changes to metering or data arrangements, depending on the capability of the existing meter.

The reform is being phased in over several years, and its full commercial implications are still becoming clear. But the direction of travel is certain, and the transition is already underway - migration having started in 2025 and continuing through 2026 and into 2027. Businesses should therefore treat MHHS as a live change rather than a future policy development. The organisations that understand what MHHS means for their energy management will be better placed to manage the transition than those that encounter it unexpectedly.

Section 1 - What is half-hourly settlement and why does it matter?

To understand MHHS, it helps to understand how electricity settlement currently works for most businesses.

The UK electricity market operates in half-hourly trading periods. Generators produce electricity, suppliers buy it, and the market settles every thirty minutes based on what was actually generated and consumed. However, most electricity meters in the UK - including the majority of commercial meters - do not measure consumption in half-hourly intervals. They record total consumption over longer periods (monthly or quarterly), and the settlement process uses estimated profiles to allocate that consumption across half-hour periods.

These estimated profiles are based on average consumption patterns for customers in similar categories - they are not based on what your particular site actually did during each half-hour period. This means:

• Your supplier has to estimate your half-hourly consumption when buying electricity on your behalf
• The estimation introduces error, which creates imbalance costs that the market has to absorb
• You do not benefit from time-of-use pricing that reflects what electricity actually costs at different times of day
• Your bill does not reflect the real value of shifting consumption away from peak demand periods

Half-hourly settlement resolves this by measuring and settling every customer's consumption in actual half-hourly intervals. Half-hourly settlement allows supplier settlement to reflect actual consumption much more closely, reducing reliance on estimated consumption profiles.

Section 2 - What MHHS involves

MHHS is the programme to extend half-hourly settlement to all electricity customers - domestic and commercial - in Great Britain. It is being delivered by Elexon, the body that operates the electricity settlement system, under direction from Ofgem.

The programme involves several interconnected changes:

New metering infrastructure. Customers without half-hourly capable meters will need smart meters or advanced metering infrastructure (AMI) that can record and transmit half-hourly consumption data. In many cases this is already in place through the smart meter rollout; in others, meter upgrades will be required.

New data flows. The way consumption data moves from meter to Data Collector to Data Aggregator to settlement is being restructured. New systems, new data standards, and new timescales are involved.

New market codes and processes. The rules governing how settlement works, how suppliers buy electricity, and how balancing is managed are being updated to reflect the half-hourly settlement model.

New settlement calendar. The timescales for initial settlement, reconciliation, and final settlement are being revised.

The programme is being delivered in phases, with suppliers migrating customers into the new settlement arrangements over the course of the implementation period.

Section 3 - What MHHS means for businesses already on half-hourly meters

If your business already has half-hourly metered supplies, MHHS changes the settlement infrastructure rather than your metering setup. The key implications:

Settlement data flows are changing

The systems and services responsible for collecting, processing and passing consumption data into settlement are changing under MHHS. During migration, businesses should keep a close eye on data completeness and investigate any unexpected gaps or anomalies.

Contract pricing may evolve

As half-hourly settlement extends to all customers, the basis on which suppliers price commercial contracts is likely to evolve. Suppliers currently carry estimation risk - the difference between what they forecast you will use and what you actually use. As settlement becomes more granular and more accurate, this forecasting risk reduces, which may affect how contracts are structured and priced.

For organisations on flexible procurement arrangements, more granular consumption data may also support better forecasting, profiling and purchasing decisions.

Time-of-use signals will strengthen

MHHS creates a stronger foundation for time-of-use and other more flexible tariff structures, where charges can better reflect when electricity is consumed.

Section 4 - What MHHS means for businesses not yet on half-hourly meters

For organisations with non-half-hourly meters - typically smaller commercial sites - MHHS means that smart meter installation and the transition to half-hourly settlement is coming, on a timeline set by the regulator rather than by the customer.

The practical implications:

Smart meter installation. If your site does not already have a smart meter, your supplier will need to install one as part of the MHHS migration. This is generally straightforward but requires coordination with your supplier and brief access to the meter.

New data availability. Once on a half-hourly smart meter, you will have access to half-hourly consumption data that was not previously available. This data can support better energy management, more accurate billing validation, and more informed procurement decisions.

Time-of-use tariffs. Once settled on a half-hourly basis, you may be offered time-of-use tariffs that reflect the actual cost of electricity at different times of day. Depending on your consumption profile, these can represent either an opportunity for savings or an increase in costs - the key is understanding your load profile before committing to a tariff structure.

Billing accuracy. One of the expected benefits of MHHS is improved settlement accuracy through greater use of actual half-hourly consumption data. Businesses should still continue to validate bills and monitor data quality during the transition.

Section 5 - MHHS and the broader energy data landscape

MHHS does not exist in isolation. It is part of a broader evolution in how energy data is collected, used, and commercialised in the UK electricity market.

Other significant developments running in parallel include:

The National Energy System Operator (NESO). The National Energy System Operator, NESO, took over from National Grid ESO and has a wider role in planning and operating the future energy system. Its work sits alongside reforms such as MHHS as the electricity market becomes increasingly data-led and flexible.

Smart Meter Implementation Programme (SMIP). The government's smart meter rollout is the metering infrastructure layer beneath MHHS. Progress on smart meter installation determines how quickly MHHS can be extended to smaller customers.

Flexibility markets. MHHS creates the data infrastructure that makes widespread demand flexibility possible. As flexibility markets develop - allowing businesses and households to be paid for reducing consumption at peak times - half-hourly settlement is the foundation on which those markets operate.

Energy data and privacy. Half-hourly consumption data is significantly more granular than monthly or quarterly data. The governance frameworks for how this data is stored, accessed, and used are evolving alongside the technical reforms.

Section 6 - What organisations should do now

For most businesses, MHHS is a background reform that will be managed largely by suppliers and metering agents. But there are specific actions that forward-thinking energy managers should consider:

Understand your current metering status. Know which MPANs have already migrated, understand the metering and data arrangements behind each site, monitor data completeness through the transition, and investigate unexpected billing or consumption changes rather than assuming they are simply a consequence of MHHS.

Review your data flows. For sites already on half-hourly settlement, confirm that your consumption data is flowing correctly through your Data Collector and Data Aggregator, and that gaps or anomalies are being identified and resolved promptly.

Engage with your energy management platform. If you are using a platform like elexi, confirm that it is configured to handle the new data flows that MHHS introduces. Platform providers should be updating their systems to accommodate the MHHS changes.

Consider the flexibility opportunity. If your organisation has significant flexibility in when it uses energy, MHHS creates an improved foundation for demand response and load shifting programmes. This is worth exploring with your energy adviser as the reform progresses.

Monitor billing accuracy through the migration. Data quality issues during MHHS migration can feed through into billing errors. Maintaining close oversight of your invoices through the transition period is prudent.

The bottom line

MHHS is the most significant structural reform to UK electricity settlement in a generation. For organisations already managing energy professionally - with consolidated data, active procurement strategies, and regular billing audits - it is a reform that improves the accuracy and granularity of the information they work with.

For organisations still running energy on autopilot, MHHS is a signal that the electricity market is becoming more sophisticated and more data-driven. The organisations that build the infrastructure and expertise to operate in that environment now will have a structural advantage over those that catch up later.