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What is Estimated Annual Consumption and how does it impact electricity bills?

Every month, millions of households and businesses across Britain pay for their electricity by direct debit based on a calculation most have never heard of, called Estimated Annual Consumption (EAC).

Despite its direct impact on consumer finances and its central role in how the energy market operates, EAC receives remarkably little explanation from the suppliers who rely on it.

This guide sets out everything you need to know about EAC. Here is what we cover:

• How Estimated Annual Consumption impacts electricity bills
• How Estimated Annual Consumption is calculated
• Where is the Estimated Annual Consumption used?
• How smart meters affect Estimated Annual Consumption
• Why your Estimated Annual Consumption may be inaccurate

What is Estimated Annual Consumption (EAC)?

Estimated Annual Consumption (EAC) is a figure used in the British energy industry that represents how much electricity (in kWh) a meter point is expected to consume over the next 12-month period.

Because older meter types that do not automatically send meter readings are still common, the energy market needs a consistent way of estimating their power consumption.

For these consumers, EAC directly impacts unit charges on monthly bills and the amount a supplier takes via direct debit each month.

💡 This article focuses on Estimated Annual Consumption for electricity. The equivalent for business gas prices is called “Annual Quantity”.

How Estimated Annual Consumption impacts electricity bills

Some energy suppliers specifically state the Estimated Annual Consumption that they are using on their electricity bills. Others do not, but still use the EAC in the background of their calculations.

This section explains the two key impacts of Estimated Annual Consumption on domestic and business electricity bills.

Estimated meter readings

The unit domestic and business electricity price per kWh section of a bill is calculated based on meter readings at the start and end of the billing period.

Where actual meter readings are not available, your supplier will use Estimated Annual Consumption to calculate these meter readings.

Estimated Annual Consumption, therefore, affects how much you owe your supplier on your electricity bill.

When an actual meter reading is received, your supplier will reconcile previous estimates against real consumption figures. Depending on whether your usage was over or underestimated, this can result in either a catch-up charge or a credit on your next bill.

Unexpected charges arising from this reconciliation are one of the most frequent sources of complaints against business energy suppliers.

Direct debit collections

Domestic and micro business electricity customers typically pay their electricity bills by direct debit.

Direct debits are typically set so that the supplier collects the expected annual cost of the contract in 12 equal monthly payments.

Where the EAC is set too high by a supplier, they will collect more money from the customer than is actually owed, leading to a credit balance.

Ofgem requires suppliers to conduct an annual direct debit review and to notify customers if their direct debit amount changes. Suppliers are also required to promptly refund credit balances on request.

How Estimated Annual Consumption is calculated

This section explains the broad methodology used to calculate Estimated Annual Consumption.

In the British energy industry, there are broadly two types of EAC in use:

• EAC Calculation Methodology – A formalised calculation for EAC using a prescriptive methodology. The EAC for each individual supply point (MPAN) is recorded on a central Meter Point Administration Service accessible by energy suppliers.
• Individual supplier EAC – Individual suppliers typically use their own EAC calculations to manage billing and direct debit collection for their customers.

In both cases, here is how Estimated Annual Consumption is calculated:

Actual consumption data

The EAC calculation relies on actual consumption data from historical meter readings from domestic or business electricity meters. This includes:

• Manual meter readings submitted by the customer.
• Manual meter readings submitted by the supplier.
• Automatic meter readings from smart and half-hourly meters.

The EAC calculation prioritises meter readings from the previous 12 months, as these are considered the most representative data.

Where recent meter reading data is not available, the EAC estimate will fall back on industry default values.

Time and seasonal normalisation

Manual meter readings are typically not recorded at regular intervals, so the EAC calculation must convert these into a consistent annual figure.

A standardised process of time normalisation is used, whereby the intervals between readings are scaled up to 12 months in a way that accounts for typical seasonal variations in consumption.

Weather normalisation

Domestic and business energy consumption is affected by weather conditions.
To account for abnormally cold or hot weather, the EAC calculation adjusts consumption to a standard weather year.

Where is the Estimated Annual Consumption used?

Estimated Annual Consumption is not just used for billing and collecting payments from customers; it also plays a role in other key processes of the energy system.

In some cases, the EAC is a standardised, industry-wide calculation. In others, individual suppliers may apply their own methodology.

Electricity bills and direct debit collection

EAC type: Non-standardised EAC calculations

Domestic and business energy suppliers use their own internal consumption estimates when setting their customers’ monthly direct debit amounts.

The regulator Ofgem does not specifically require suppliers to use the standardised EAC calculation, but requires their EAC calculations to be “fair and reasonable”.

Tariff quotation

EAC type: Non-standardised EAC calculations

When an energy supplier prepares a quote for a prospective customer, they will provide a headline estimated annual cost for the tariff.

The estimated annual cost typically relies on their own methodology for EAC, which can differ significantly from one supplier to another.

Our business electricity comparison service cuts through this complexity by applying a consistent EAC across all quotes, enabling a fair comparison between them.

Supplier switching process

EAC type: Standardised, Centrally held.

Estimated Annual Consumption plays a key role when a customer chooses to switch energy suppliers.

It is common for a switch to occur on a date for which no meter reading is available. In these cases, EAC is used to calculate an agreed estimated meter reading at the point of switch, ensuring that bills raised by both the incoming and outgoing suppliers are consistent.

Find out more in our full guide to switching business energy suppliers.

Wholesale market settlement

EAC type: Standardised, Centrally held.

In the wholesale electricity market, energy suppliers purchase power from generators such as UK wind farms and nuclear power stations.

The electricity purchased by suppliers is matched against their customers’ consumption every 30 minutes of the day. This process is called market settlement and is administered by the organisation Elexon.

For domestic and small business properties, the settlement process relies on estimated consumption using the EAC methodology.

💡 The settlement process is being updated to use automatic meter readings every 30 minutes under the Market-wide half hourly settlement reform.

Distribution Use of System (DUoS) charging

EAC type: Standardised, Centrally held.

DUoS charges are levied by Distribution Network Operators on licensed energy suppliers for the use of regional electricity grids to deliver power to customers.

The EAC calculation is used to allocate unit-based DUoS charges to each individual customer.

How Estimated Annual Consumption changes over time

Estimated Annual Consumption is not a static figure. Instead, it provides a live estimate that is updated each time a new meter reading is received.

The EAC calculation typically prioritises the most recent meter reading data, so a single new meter reading can have a significant impact on the overall calculation.

For example, if a customer installs commercial solar panels and actual consumption falls significantly below the previous EAC, a new meter reading will trigger a significant downward revision to the EAC.

Manual supplier adjustments to EAC

Energy suppliers can make manual adjustments to the Estimated Annual Consumption used for billing and direct debit collections.

Examples of when a supplier might amend the EAC include:

• Change in customer circumstances – For example, if a landlord reports that a property is unoccupied, the supplier may reduce the EAC to reflect this.
• Tariff changes and contract renewals – When a customer moves to a new tariff, a supplier may review and adjust the EAC accordingly.

These adjustments to the EAC will typically affect the next monthly electricity bill issued by the supplier.

How smart meters affect Estimated Annual Consumption

Smart domestic and smart business energy meters take and transmit automatic meter readings continuously and as often as every 30 minutes.

This has two implications for how EAC is used in the raising and calculation of electricity bills.

No estimates required for unit charges

When customers have a functioning smart meter, an energy supplier can use actual data for the opening and closing meter readings on their monthly bills.

This means that Estimated Annual Consumption is no longer relied upon, and the electricity bills received will be an accurate reflection of actual power usage during the month.

More accurate estimates for direct debit collections

For customers with smart meters, direct debit calculations may still rely on Estimated Annual Consumption to calculate expected annual costs.

With live consumption data from smart meters, the Estimated Annual Consumption calculation has access to much more granular data compared to a supply point that submits occasional manual meter readings.

This allows the Estimated Annual Consumption figure to be continually updated and refined, enabling direct debits to respond more quickly to customers’ changing consumption habits.

Why your Estimated Annual Consumption may be inaccurate

Estimated Annual Consumption is a forecast of future usage, and some inaccuracies are inherent in the estimation process, while others are caused by the customer’s own circumstances or supplier error.

Here we will summarise the key reasons for inaccuracy in the EAC.

Inherent limitations of EAC

The EAC uses historical data to estimate future consumption, assuming that future usage will reflect past consumption.

Consequently, the Estimated Annual Consumption cannot take into account changes in consumer behaviour that are not reflected in meter reading data. Common examples include:

• Changes to occupancy
• New high-consumption appliances or equipment, such as EV charging
• Improvements in domestic or business energy efficiency
• Behavioural changes

Data quality issues

The EAC calculation relies on accurate historical data and can be affected by the following issues:

• Infrequent actual meter readings – The less data available for the EAC, the more assumptions the calculation needs to make, making it more likely that actual results will diverge from the estimate.
• Poor read quality – Errors in meter readings are common. Misread meters and readings taken from the wrong meter can all introduce errors into the consumption history that may skew the EAC.

Supplier system and process failures

A key responsibility of licensed energy suppliers in the retail energy market is to record customers’ manual meter readings on the central industry system.

Inaccuracies in the EAC can be introduced by poor practices on the part of your supplier, including:

• Failure to proactively obtain readings – Suppliers are required to make reasonable attempts to obtain actual meter readings periodically.
• Poor handling of submitted reads – Readings submitted by customers via a supplier’s app or website can be delayed or missed due to problems with the validation processes used by each supplier.
• Billing system errors – Supplier billing systems are complex and can contain configuration errors that cause consumption estimates to be calculated or applied incorrectly.

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