MHHS, explained.

What MHHS is, and what it replaces

Electricity settlement is the process that decides how much energy each supplier bought on your behalf in each half hour, and therefore what it owes. For a site with a half-hourly meter that has always been arithmetic: the meter records a number for each of the 48 settlement periods in a day, and the number is used.

For everyone else it has been an estimate. A non-half-hourly supply carries a profile class in its meter point number, and settlement spreads a meter reading across the half hours using the average shape of everybody else in that class. Elexon defines eight: classes 1 and 2 for domestic customers, 3 and 4 for non-domestic unrestricted and Economy 7 supplies, and 5 to 8 for non-domestic maximum demand customers graded by peak load factor. BSC modification P272, implemented in April 2017, made half-hourly settlement mandatory for classes 5 to 8. Classes 3 and 4, which is most small and medium businesses in the country, have stayed on the estimate ever since.

MHHS ends that. Once a meter point has migrated it is settled from its own half-hourly data, and the profile class stops deciding anything.

The instruments it is delivered under

Ofgem decided to proceed on 20 April 2021, on the Target Operating Model produced by the industry Design Working Group, with an estimated net benefit to consumers of between £1,559 million and £4,509 million over 2021 to 2045. The codes then had to be rewritten to match. Four changes carry it:

The timetable as it stands today

These are the milestone dates published by the MHHS Programme and by Elexon at the date this guide was reviewed. They are not the dates the programme started with, and the section after this one says how far they have moved.

1. 22 Sep 2025M10, central systems ready

   The Elexon central services go live and are able to accept migrating meter points. Nothing can migrate before this.

   →
2. 22 Oct 2025M11 and M12, migration starts

   The 18 month migration window opens, first for unmetered and advanced metered supplies, then for smart and non-smart meters.

   →
3. 28 Oct 2026M14, qualification deadline

   Every supplier must be qualified to operate under the new arrangements. From this point a migrated meter point cannot go back to non-half-hourly settlement on a change of supplier.

   →
4. 7 May 2027M15, migration ends

   All 33 million meter points are on the new arrangements. Non-half-hourly settlement stops existing.

   →
5. 2 Jul 2027M16, new settlement timetable

   Cutover to the shortened settlement runs, which is where the benefit the programme was justified on actually lands.

Where the migration has actually got to

Elexon reported on 17 June 2026 that more than 11.3 million migrations had completed and about a third of the metering systems in Britain were operating under half-hourly settlement, with 11 suppliers actively migrating and two suppliers about three quarters of the way through. The MHHS Programme announced on 22 July 2026 that half of industry meter points had migrated. Elexon expects around 80 per cent by October 2026.

The services it creates, and the roles it ends

MHHS is a rebuild of the central plumbing, not a tweak to it. Elexon switched on five new central systems at the readiness milestone, and three new supplier-appointed data services take over the work the old data collector and data aggregator roles did.

One item on that list is not what its name suggests. The Load Shaping Service does not abolish load shapes: shapes are still needed where a smart meter has only register readings rather than settlement period data. The difference is that the shape now comes from what comparable meters actually did.

Fourteen months to four

The reason the programme was worth doing is not the data for its own sake. It is that a settlement day currently takes about 14 months to finish, and afterwards will take four. Everything reconciled inside that window reaches your invoice sooner and smaller.

Network charging moves with it. Southern Electric Power Distribution states in its 2026/27 charging statement that invoices on the aggregated approach are reconciled over approximately 14 months to reflect later and more accurate consumption figures, and that this will reduce to four months following MHHS implementation. That is the same reduction, arriving on the same charge that the DUoS guide describes in detail.

What actually changes on a business bill

Settlement volume for a non-half-hourly supply is a product of three terms. MHHS collapses the first two into one measured number and leaves the third alone.

The third term stays. The line loss factor grosses metered volume up for the electricity lost as heat in the network, and it applies before and after migration alike.

From that one substitution the whole answer follows, and it is simpler than most coverage of MHHS makes it sound. A charge whose rate is the same in every half hour does not care what shape the volume had, because the total is the total. A charge whose rate varies by half hour cares about nothing else. Sorting the lines on a business electricity bill that way gives the whole answer.

The second row is the one worth reading twice. The Capacity Market Supplier Charge is charged on demand in six half hours a day, on working days between November and February, and on nothing else. For a non-half-hourly site that figure has to be apportioned from a profile, which means the line cannot be checked against anything. After migration it is a measurement of your own site. Meanwhile BSUoS is one fixed national tariff per period and the transmission demand residual is a flat daily band charge, so neither of them moves at all.

The same site, before and after

Take a non-domestic site on the Southern Electric Power Distribution network, whole current metered, on profile class 03 today. Assume it draws 30 kW between 07:00 and 17:00 Monday to Friday and 3 kW at every other time, with no seasonal variation. The shape is the assumption and it is labelled as one. Every rate below is published for the 2026/27 charging year.

The 2026/27 charging year runs 1 April 2026 to 31 March 2027, which is 365 days, and 1 April 2026 and 31 March 2027 are both Wednesdays, so it holds 261 weekdays and 104 weekend days. Southern sets its red band at 16:30 to 19:30 on weekdays including bank holidays all year, its amber band at 07:00 to 16:30 and 19:30 to 22:00 on weekdays and 09:30 to 21:30 at weekends, and green everywhere else.

Distribution, on measured bands instead of profiled ones

Assumed demand, 07:00 to 17:00 on weekdays

30 kW

Assumed demand, every other hour

3 kW

Annual consumption that implies

96,750 kWh

Units falling in the red window, 6.07 per cent

5,872.5 kWh

Units falling in the amber window, 82.78 per cent

80,086.5 kWh

Units falling in the green window, 11.15 per cent

10,791.0 kWh

Red at 12.061p per kWh

£708.28

Amber at 1.606p per kWh

£1,286.19

Green at 0.082p per kWh

£8.85

DUoS unit charges for the year

£2,003.32

Those are the Southern Non-Domestic Aggregated Band 2 rates for 2026/27, and here is the point of the example: they are the same rates before and after migration. What changes is which of the three each unit meets. Before migration the split is the one the profile class implies. After migration it is the one above, because the meter measured it.

The sensitivity is easy to state and hard to argue with. One percentage point of this site annual consumption, 967.5 kWh, moved from the amber rate to the red rate costs 10.455p per kWh, or £101.15 a year. Whether migration raises or lowers this line depends entirely on whether the class profile overstated or understated the evening peak of this particular site, and nobody can tell you which without the data. Anyone who says MHHS will save your business money has not looked at your meter.

Transmission, where the meter type decides the answer

The site sits in TNUoS demand zone 13, Southern. For 2026/27 that zone is charged £7.354150 per kW of triad average demand on the half-hourly basis, and 1.008120p per kWh of consumption between 16:00 and 19:00 every day of the year on the non-half-hourly basis.

Units consumed 16:00 to 19:00 across the year

10,332 kWh

Non-half-hourly basis, at 1.008120p per kWh

£104.16

Demand across the triad half hours, site closed by 17:00

3 kW

Half-hourly basis, at £7.354150 per kW

£22.06

Difference, if the basis changes

£82.10

Distribution charging draws the same line in the same place. Southern receives aggregated consumption data for every migrated meter point with a whole current connection type, and site-specific data for low voltage, high voltage, extra-high voltage and unmetered connection types. Aggregated billing carries a fixed charge and three unit charges and nothing else, so migrating does not by itself bring capacity or reactive power charges to a small site.

What changes on the invoice itself

MHHS has no line of its own, so the visible evidence is in the identifiers and in the reference data behind them. These are the things that move, and each one can be checked against a document.

The first row is the one worth acting on. If the front of your meter point number still reads 03 or 04, your site has not migrated yet and every time-varying charge on the invoice is still being calculated from a class average. If it reads 00, it has.

How to check it, and what goes wrong

There is nothing to check on MHHS itself. What there is to check is the invoice either side of a migration, because a change of settlement basis mid-period is exactly the kind of event that produces a wrong bill.

• Find the migration date. Ask your supplier when the meter point migrated. A billing period spanning it is settled on two different bases, and the invoice has to split at that date.
• Check the profile class digit. A migrated meter point carries profile class 00. A supplier system still charging a migrated site as though it were profile class 03 is charging it on data that no longer exists.
• Ask for the banded volumes, not the total. Once you are settled half-hourly, the network operator has your split across red, amber and green. If the invoice shows one consumption figure and one blended rate, nothing in the distribution line can be reconstructed.
• Watch for charges that should not have appeared. Migration alone does not put a small site onto capacity and reactive power charges. Southern bills properties under transitional protection arrangements for MHHS with fixed and unit charges only, in the same manner as aggregated charges.
• Expect reconciliations, then fewer. During the changeover the volume behind a levy can be restated more than once. After the settlement timetable cuts over, the window inside which that can happen shortens from about 14 months to four.

What is still to be decided

Two things are genuinely open, and it is worth separating them from the timetable, which is settled unless Ofgem approves another change.

The length of the migration window

Ofgem asked the programme in the CR055 decision to examine whether the 18 month migration period could be shortened, and no change has followed. What is certain is that after the supplier qualification milestone on 28 October 2026, a migrated meter point cannot return to non-half-hourly settlement on a change of supplier, so the direction of travel is one way from that date.

The shortened timetable arrives in steps, not at once

The headline is 14 months to four, and both halves are true, but they are separated by six months. The final reconciliation run drops to seven months for settlement days from 1 October 2026 and to four months for settlement days from 1 April 2027, and the initial settlement run does not compress until 1 July 2027. A reconciliation you receive in the meantime is being produced under a timetable that is itself mid-change.

Deep dives and edge cases

The main path above answers the question most businesses arrive with. These come up often enough to answer and not often enough to interrupt it.

Questions