Half-hourly settlement data

The difference between half-hourly meter data, electricity settlement and retail billing, including current MHHS migration and domestic data choices.

Electricity settlement is the industry process that works out how much energy each supplier’s customers used or exported in each settlement period. Those periods are 30 minutes long, so there are normally 48 in a day.

Half-hourly settlement does not necessarily mean that every one of those figures came directly from the property’s meter. A communicating smart or advanced meter can provide actual interval data. Where it cannot, the industry may have to estimate the shape from register readings and data from similar supplies.

That distinction matters. Market-wide Half-Hourly Settlement changes how the industry allocates electricity and cost between suppliers. It does not, by itself, move a household onto a time-of-use tariff or make an estimated retail bill accurate.

Keep three records separate

The same property can have three related but different records:

meter data records cumulative registers and, where the equipment supports it, consumption or export in individual half-hours
settlement data allocates energy to an import or export MPAN for the wholesale-market process and can include validated estimates where actual data is unavailable
billing data is what the supplier uses with the customer’s tariff terms to calculate a bill or export payment

A solar, battery, EV-charger or heat-pump app creates another dataset again. Device telemetry may show power changing second by second, but it is not the regulated meter record and does not replace it for billing or settlement.

This is why two graphs can disagree without either necessarily being faulty. They may cover different boundaries, intervals or losses. Compare the meter serial number, import or export direction, time zone and period before trying to reconcile them.

Why settlement uses half-hour periods

Electricity is bought, sold and balanced in settlement periods. Elexon administers the Balancing and Settlement Code arrangements that compare contracted energy with metered allocations and calculate the resulting imbalance positions.

Under the legacy non-half-hourly system, most domestic and smaller-business meters supplied occasional cumulative readings. Those totals had to be spread across the day using standard profiles. The result could be correct for the total period but only an estimate of when the electricity was used.

A working smart meter can show the property’s actual pattern. That gives a supplier a stronger reason to encourage charging, heating or battery operation when wholesale and system costs are lower. It also makes it possible to calculate a retail tariff whose price genuinely changes by time period.

Actual data is still not guaranteed for every interval. Missing communications, rejected data or a non-smart meter require estimation. Under the new arrangements, Elexon’s Load Shaping Service uses validated data from groups of supplies to create the shapes used where individual half-hourly values are not available. That is more current and granular than the old profile-class method, but it is still not the same as measuring that home’s exact timing.

The MHHS transition

Market-wide Half-Hourly Settlement, usually shortened to MHHS, is moving Great Britain’s electricity meter points onto the new settlement arrangements.

As at 22 July 2026:

migration began on 22 October 2025
the current programme date for suppliers to be able to operate under the new arrangements is 28 October 2026
full transition is scheduled for 7 May 2027
the cutover to the shorter settlement timetable is scheduled for 2 July 2027

These are programme dates, not promises about a particular household. Elexon publishes live migration information because the number of transferred meters changes throughout the programme.

A supplier may migrate an MPAN in the background. The customer does not normally need to apply, and migration alone does not change the meter, tariff or contractual price. A single-rate tariff remains single-rate unless the supplier changes the contract in accordance with the applicable rules.

MHHS also covers supplies without usable actual half-hourly data. A traditional meter may continue to be read through its registers while the new services estimate the distribution of that consumption across settlement periods. A smart-meter exchange may still be needed before the customer can use a tariff or service that requires actual interval readings.

Domestic smart-meter data choices

A smart electricity meter stores consumption in half-hour intervals. Ofgem’s current consumer guidance sets different default sharing levels according to when the meter was installed and whether there has since been a supplier switch or new contract.

For a domestic customer whose smart meter was installed before 3 November 2022, with no supplier switch or new contract since that date:

the normal sharing level is daily
the customer can opt in to half-hourly sharing
the customer can opt down to monthly sharing

For a domestic customer whose meter was installed, supplier changed or new contract agreed after 3 November 2022:

the normal sharing level is half-hourly
the customer can opt down to daily sharing

The familiar statement that domestic half-hourly data is always opt-in is therefore out of date. These choices also sit alongside access needed for billing and other regulated purposes. Marketing use requires separate permission.

A time-of-use tariff or managed-energy service may contractually require detailed readings. Reducing the sharing level may make that product unavailable even where the general meter setting can be changed. Ask the supplier what happens to the tariff before opting down.

What half-hourly data enables

Actual interval data can support:

import tariffs with fixed off-peak windows or prices that vary by half-hour
export tariffs that value electricity differently by time
managed EV charging, battery dispatch and heat-pump optimisation
flexibility services that need to establish when consumption changed
clearer comparison between an intended schedule and what passed through the boundary meter

The SEG (Smart Export Guarantee) requires an export meter capable of recording export in half-hourly periods. A contract may still pay one export rate at all times. Export MPAN enrolment and delivery of readings to the export supplier are separate parts of the account setup.

Checking whether the data is usable

Do not rely only on an in-home display or equipment app. For an import or export tariff that uses half-hourly readings, check:

the correct meter serial number is registered to the relevant MPAN
the meter has the required import or export register
the supplier can retrieve interval readings remotely
the supplier’s account shows complete readings for recent days
the tariff has been applied from the confirmed start date

A smart meter can continue measuring cumulative consumption when its communications are not working. In that situation the display may look normal while the supplier receives no interval data. Take and retain dated photographs of the relevant registers, but recognise that manual totals cannot recreate the exact timing of missing half-hours.

Short gaps may be estimated under the relevant settlement or tariff rules. Persistent gaps can affect smart-tariff bills, export payments and eligibility for flexibility services. Report them to the supplier and ask whether the problem is the meter, communications, MPAN setup, data validation or the tariff account rather than accepting the general answer that the meter is “smart”.

Downloading and comparing data

The supplier or an authorised service may offer a half-hourly download. Before using it for financial modelling, check:

whether timestamps mark the start or end of each period
whether times are UTC or local clock time
how the spring and autumn clock changes appear
whether values are actual, estimated or missing
whether import and export are in separate files or registers
whether the unit is kWh for the interval or average kW

For billing disputes, preserve the original file and bill as well as any spreadsheet derived from them. Equipment-portal exports can help diagnose behaviour, but the supplier’s meter data and tariff rules determine the retail calculation.