Half-hourly meters: what they are, who needs one and what they cost

What is a half-hourly meter?

A half-hourly meter is an electricity meter that records how much electricity your site uses in each half hour of the day. A normal day has 48 of these periods. The readings are collected remotely by a data service, which checks them and passes them on for billing. You may also see them called HH meters. The supply licences call a meter an advanced meter if it can record readings at least every half hour (every hour for gas) and your supplier can read it remotely.

The half hour matters because electricity in Great Britain is settled in half-hour periods. With a half-hourly meter, your supplier is charged for what your site actually used in each period. Without one, the industry estimates how your use spreads across the day from standard patterns, called profiles.

For you, the main difference is that you can be charged for when you use electricity, as well as how much. This guide covers the rules in Great Britain.

How to tell if you have a half-hourly meter

There are two quick checks on your electricity bill.

1. The top row of your MPAN. Your full supply number, or MPAN, has a top row above the main 13-digit number. If the first two digits of the top row are 00, your supply is settled half-hourly. The numbers 01 to 08 are profile classes, used for meters whose use has been estimated from standard patterns, though some meters keep their profile class after moving to half-hourly settlement (see below).
2. The charges. A capacity or availability charge in kVA, or a reactive power charge in kVArh, is a strong sign of a half-hourly supply, though a CT-metered site won't have them in its first 12 months after moving to half-hourly settlement. Not having them doesn't rule one out, because half-hourly sites with whole-current meters don't pay these charges. Our guide to kVA capacity charges explains who pays.

The codes on the top row are changing as meters move to the new settlement arrangements described below. Any meter that has moved, including smart meters, shows 00 if it no longer has a profile class. Meters in profile class 02 or 04 keep that code. By 7 May 2027, every meter is due to be settled half-hourly, whatever its top row shows. So the charges are now the better sign of a half-hourly meter. If you're not sure, ask your supplier whether your meter is settled half-hourly, and whether it's a CT meter.

Which businesses need a half-hourly meter?

Three rules decide this.

Sites with a maximum demand over 100 kW. Any site whose maximum demand is over 100 kW must be settled half-hourly.

Profile classes 5 to 8. These are business sites with maximum demand metering, grouped by load factor, which compares a site's average demand with its peak:

• profile class 5: a load factor below 20%;
• profile class 6: 20% to 30%;
• profile class 7: 30% to 40%;
• profile class 8: over 40%.

Since 6 April 2014, suppliers have had to supply sites in these classes only through advanced meters, unless they can't fit one despite taking all reasonable steps. A change to the industry rules called P272, approved by Ofgem on 29 October 2014, then made half-hourly settlement mandatory for them. After an extension, the move had to be complete by 1 April 2017.

Sites with CT advanced meters. Supplies with a load over 100 amps per phase use current transformer (CT) meters. Smaller supplies use whole-current meters. Under another rule change, P432, approved by Ofgem on 15 January 2024, CT advanced meters that are still settled non-half-hourly must move to half-hourly settlement by market-wide settlement milestone M14, due on 28 October 2026.

Most businesses can ask for a half-hourly meter, even if they don't have to have one.

What charges appear on a half-hourly bill?

Network operators charge most larger half-hourly supplies, those with current transformer (CT) metering, on a site-specific basis, so the bill is built from more parts than a standard one. Smaller half-hourly supplies with whole-current meters are charged like other small sites, with a fixed daily charge and unit charges only. So are CT sites for the first 12 months after they move to half-hourly settlement, under DCP414, a change to the distribution charging rules that Ofgem approved in July 2023. Your supplier pays these charges, and depending on your contract, they're either included in its rates or passed through to you as separate lines.

• Unit charges by time band. Network unit charges change with the time of day, in red, amber and green bands (see below).
• A fixed daily charge for each MPAN, as on any supply.
• A capacity charge, in pence per kVA per day, on the capacity agreed for your site, often called your Maximum Import Capacity or MIC. You pay it however much electricity you use, except that a CT site pays none for its first 12 months after moving to half-hourly settlement. The network operator then sets the site's capacity from its metered data.
• An exceeded capacity charge, if your demand goes over the agreed capacity.
• A reactive power charge, in pence per kVArh, if your equipment draws power inefficiently and the reactive power goes over a set level. In the network operators' charging statements, that level is 33% of active power in a half hour, equivalent to an average power factor of 0.95, and only the reactive power above it is charged.
• Transmission charges, which for half-hourly sites partly depend on use at the busiest times of the year (see Triads below), plus a fixed daily charge set by your site's band.
• Metering and data charges for the meter operator and the data service (see below).

Ofgem says fixed-rate contracts fix your unit rates and standing charges for the length of the contract. Some contracts instead pass network and other non-energy charges through to you, so they can change. Check your terms before you agree.

Our business electricity rates page shows what businesses of each size pay per kWh.

What are red, amber and green time bands?

Each network operator splits the week into time bands for its distribution charges. Red is the peak period, when the local network is busiest. In every region it covers weekday late afternoons and early evenings, and London also has a second red period. Amber and green cover the rest of the week, with green including the night. The red unit charge is the highest of the three in every region.

The exact hours vary between regions, and our guide to DUoS charges lists them for every area. Each operator publishes its time bands and charges in a charging statement, and the charges are set each year, taking effect on 1 April.

What are Triads?

The National Energy System Operator (NESO) sets the charges for the high-voltage transmission network. For half-hourly sites, part of the transmission charge is based on use during the Triads: the three half hours of highest net demand on the national system between November and February, each at least ten full days apart.

The Triads can only be identified once the season is over. NESO publishes them afterwards: it published the Triads for winter 2025/26 on 26 March 2026. Every site also pays a fixed daily transmission charge, set by its band.

Our guide to TNUoS charges explains how Triads fit into transmission charges.

Is a half-hourly meter more expensive?

There's no single answer, because a half-hourly bill is built differently rather than simply priced higher. What you pay depends on three things.

• Your agreed capacity. The capacity charge is based on the capacity in your connection agreement, not on what you use. If your site's peak demand is well below its agreed capacity, you're paying for capacity you don't use.
• When you use electricity. Network unit charges are highest in the red band, so two sites that use the same amount of electricity can pay different amounts, depending on how much of it falls in the red band.
• Metering and data. A half-hourly meter needs a meter operator and a data service. Depending on who appointed them, you pay for these through your supplier or under a separate contract.

The data itself is useful. A reading every half hour shows exactly when your site uses electricity, including overnight and at weekends, when you may expect it to be using very little.

When you compare quotes for a half-hourly supply, check:

1. whether network and other non-energy charges are fixed or passed through;
2. whether metering and data charges are included;
3. that the capacity on the quote matches your connection agreement;
4. the total yearly cost, rather than the unit rate or standing charge alone.

Who arranges the meter operator and data service?

Every half-hourly meter needs a meter operator, which installs and maintains it, and a data service, which collects the half-hourly readings and processes them for billing and settlement. You must have a contract with a meter operator. Under the new settlement arrangements, these roles are called the Metering Service (Advanced) and the Advanced Data Service.

You can appoint them yourself, or leave it to your supplier, which will appoint them for you if you haven't. If you already have contracts with your own meter operator or data service, tell your supplier, and tell any new supplier when you switch.

Can you downgrade or remove a half-hourly meter?

Usually not. If your site's maximum demand is over 100 kW, it has to be settled half-hourly, and from 28 October 2026 so does any site with a CT advanced meter. And by 7 May 2027, every meter in Great Britain, smart or not, is due to have moved to half-hourly settlement (see below).

What you can change is your agreed capacity, by applying to your network operator. You can apply yourself, or someone you authorise can apply for you. National Grid Electricity Distribution and UK Power Networks both say:

• your capacity can only be changed once in any 12 months;
• a reduction takes effect from the first day of the next month, and can't be backdated.

National Grid Electricity Distribution doesn't charge for a reduction, as no work on site is needed. It also warns that capacity you give up is released back to the network and may be used by others, so you may have to pay if you want to increase it again later.

Before you reduce it, look at your site's peak demand over at least a full year, which your half-hourly data shows. If you go over the new capacity, you'll pay exceeded capacity charges.

What does market-wide half-hourly settlement change?

Market-wide half-hourly settlement, or MHHS, is moving every electricity meter in Great Britain to half-hourly settlement. That includes advanced meters on larger business sites, smart and non-smart meters, and unmetered supplies such as street lighting. Elexon, which runs the settlement process and manages the programme, gives these dates:

• 22 October 2025: suppliers started moving meters to half-hourly settlement;
• 28 October 2026: all suppliers must be able to work with MPANs under the new arrangements;
• 7 May 2027: all meters moved;
• 2 July 2027: settlement moves to a four-month timetable. A cut from 14 months to seven, for settlement days from October 2026, has already been agreed.

By 25 September 2026, the MHHS programme said 23.8 million supply numbers (MPANs) had moved to the new arrangements, 71% of the total.

If you already have a half-hourly meter, your supplier handles the move and you don't need to do anything. npower Business Solutions says MHHS won't change how existing meters are configured, and that changes are made remotely where possible, though a site visit is sometimes needed. You may see different codes on the top row of your MPAN.

Getting quotes for a half-hourly supply

It helps to have these to hand:

• your MPAN and the supply address;
• your agreed capacity in kVA, from your bill or your connection agreement;
• recent half-hourly data, from your supplier or data service;
• your contract end date;
• details of any meter operator or data service you've appointed yourself.

If your contract end date has passed, you may be on deemed or out-of-contract rates, which are usually higher than contract rates.