MHHS explained: what market-wide half-hourly settlement means for your business
Market-wide Half-Hourly Settlement is moving every meter in Great Britain to half-hourly settlement. Here are the key dates, the new MSA, ADS and SDS roles, and a practical checklist for your sites.
Market-wide Half-Hourly Settlement (MHHS) changes how every electricity meter in Great Britain is settled, and it is already well under way. If your business has half-hourly meters, most of the changes happen behind the scenes, with new agent roles, new data processes and new contract paperwork, but they can still affect your bills and your data. This guide sets out the timeline, the new roles and what to check.
Key points
- MHHS is Ofgem's programme, run by Elexon, moving around 33 million meters in Great Britain to half-hourly settlement.
- Supplier migrations began on 22 October 2025, and the full migration deadline is May 2027.
- The meter operator and data collector roles for advanced meters are replaced by Metering Service Advanced (MSA) and Advanced Data Service (ADS).
- Even sites that are already half-hourly should check their agents, data and contract terms.
What MHHS is and why it is happening
Settlement is the process that matches the electricity each supplier bought with what its customers actually used, half-hour by half-hour. Until now, only larger sites were settled using real half-hourly data. Most smaller sites were settled using profile classes: standard estimated shapes of when a type of customer uses power.
MHHS replaces those estimates with actual half-hourly data for every meter. The aim is a more accurate market, and one that can reward customers who use electricity at times when it is cheaper to supply. It is Ofgem's programme and is being delivered by Elexon, which administers the Balancing and Settlement Code.
The MHHS timeline
These dates come from Elexon's programme plan and progress updates. Plans can be revised, so check Elexon's MHHS pages for the latest position.
| Date | Milestone |
|---|---|
| 22 October 2025 | Suppliers start migrating meters to the new settlement arrangements. |
| June 2026 | More than 11.3 million migrations complete, about a third of all meters. |
| October 2026 | Elexon's plan expects around 80% of meters to have migrated. |
| 28 October 2026 | Milestone 14: all market participants qualified. |
| May 2027 | Full migration deadline. Rule change P487 limits suppliers who miss it. |
For businesses, the practical point is that your supplier decides when each of your meters migrates. You do not need to apply, but you should know where each site is in the process.
The new agent roles
Every half-hourly site relies on service providers, often called agents, to install and maintain the meter, collect its data and process it. MHHS renames and reorganises these roles.
| Old role | Role under MHHS | What it does |
|---|---|---|
| Meter Operator (MOP) for half-hourly and advanced meters | Metering Service Advanced (MSA) | Installs, maintains and repairs advanced meters, including CT-operated meters. |
| Half-Hourly Data Collector (HHDC) | Advanced Data Service (ADS) | Collects and processes data from advanced meters (HH, CT and AMR). |
| Non-half-hourly data collection for smart meters | Smart Data Service (SDS) | Collects and processes half-hourly data from smart meters. |
| Half-Hourly Data Aggregator (HHDA) | Market-wide Data Services, run centrally by Elexon | Aggregates data for settlement. |
If you contract directly with a meter operator or data collector, expect paperwork to be updated as your meters move to the new roles. If your supplier arranges these services, the charges may appear on your bill under new names.
What changes if you already have half-hourly meters
Sites over 100 kW, and former profile class 05 to 08 sites moved across by P272, are already settled half-hourly. For them, MHHS is mainly a change to the systems and roles behind settlement rather than to the meter on the wall. Even so, any migration can create problems, such as:
- data gaps while services move, leading to estimated consumption on bills;
- metering or data charges billed twice, by an old and a new provider;
- contracts with the old agents running on after the role has changed;
- delays in fixing meter faults if it is unclear who is responsible.
What changes for smaller sites
Sites with smart meters, and other sites that used to be settled on profiles, are being settled using actual half-hourly data. Suppliers may offer more tariffs that vary by time of day as a result. A multi-site business may end up with a mix of advanced and smart-metered sites, each with a different data service. Bringing that data together is covered in our guide to half-hourly data across multiple sites.
MHHS checklist for businesses
- List every MPAN you are responsible for and note which are advanced (CT or HH) and which are smart.
- Ask your supplier whether each MPAN has migrated, and if not, when it is planned.
- Confirm who provides your Metering Service Advanced and Advanced Data Service, and check that any contracts are in date.
- Check recent bills for estimated data, duplicated metering charges or unfamiliar charge names.
- Download and keep your half-hourly data history in case of gaps.
- Read your supply contract for clauses that let the supplier pass on changes in industry costs.
- Note your contract end date so a renewal is not missed while migration is going on.
Our MHHS readiness service works through these checks with you, and we can arrange metering and data service contracts under the new roles.
Will MHHS change what I pay?
There is no single answer. MHHS changes how consumption is settled. It does not by itself change the rates in a fixed contract, although some contracts allow certain industry cost changes to be passed through. When contracts renew, suppliers will price them on actual half-hourly data. Sites that use a lot of power in the early-evening peak may see that reflected in prices, while sites that can move load to cheaper periods may benefit. Knowing your own profile, and understanding DUoS time bands, puts you in a better position at renewal.
Get help with MHHS
If you are not sure where your sites are in the migration, or your bills have changed since your meters moved, we can check them for you. We'll look at your agents, your data and your contract terms and tell you what needs attention. For more background, see our page on understanding MHHS.
Ask for a free bill check or quote, or call 07565 147 170.
Frequently asked questions
When does MHHS have to be finished?
The full migration deadline in Elexon's plan is May 2027. Supplier migrations started on 22 October 2025, and Milestone 14, when all market participants must be qualified, is 28 October 2026. Rule change P487 places limits on suppliers that miss the deadline. Check Elexon's MHHS pages for the latest dates.
Do I need to do anything if my site is already half-hourly?
You do not need to apply for anything, because your supplier manages the migration. It is still worth checking who your Metering Service Advanced and Advanced Data Service providers are, that your data is complete, that you are not paying for metering twice and that your contract terms are clear.
What is the Advanced Data Service?
The Advanced Data Service (ADS) is the MHHS role that collects and processes data from advanced meters, including half-hourly, CT-operated and AMR meters. It replaces the old half-hourly data collection role. Smart meters use a separate Smart Data Service, and aggregation moves to Elexon's central Market-wide Data Services.
