How to compare UK energy suppliers

A whole-bill and service method for comparing domestic energy suppliers and smart tariffs.

The cheapest energy supplier is not necessarily the one with the lowest advertised unit rate. A useful comparison combines the full import bill, any export income, contract restrictions, metering requirements and evidence about how the supplier performs when something goes wrong.

For an ordinary single-rate tariff the arithmetic is simple. For a home with solar, a battery, an EV or a heat pump, the timing of consumption and export can be more important than the annual total.

Start with the right data

Use the property’s own figures where possible:

at least 12 months of electricity and gas consumption in kWh
half-hourly electricity data for time-of-use or dynamic tariffs
separate half-hourly export data for solar and battery export
current tariff name, end date and exit fee
postcode, payment method and meter configuration
any planned change, such as an EV, heat pump or larger battery

A monthly Direct Debit is not consumption. It is a payment towards the account and can include debt, credit or a supplier estimate. Use meter-based kWh instead.

Twelve months avoids comparing a winter-heavy tariff against summer usage. For a new heat pump or EV, build a separate scenario rather than pretending last year’s demand already contains the new load.

Put every quote on the same basis

Check that each quote uses the same postcode, annual consumption, payment method and start date. Then record:

Item	Why it matters
Unit rate or time-band rates	Prices the energy actually used
Standing charge	Accrues every day, including low-use days
Contract length	Determines how long the stated terms apply
Exit fee	Can erase the benefit of an early switch
Rate status	Fixed, price-cap-linked, tracker or dynamic
Meter/data requirement	Can prevent sign-up or change billing fallbacks
End-of-term treatment	Shows what happens if no new tariff is selected
VAT and discounts	Prevents a net figure being compared with a gross one

Do not compare a supplier’s “typical household” annual figure with another quote built from the home’s actual usage. Recalculate both from the same data.

For a single-rate tariff:

annual import cost = standing charges + (electricity kWh × electricity rate) + (gas kWh × gas rate)

For a multi-rate tariff, multiply the kWh in each time band by its own rate. For a dynamic tariff, apply each half-hour’s consumption to the price for that half-hour.

Understand what the price cap does

Ofgem’s price cap limits unit rates and standing charges on default domestic tariffs. It does not cap the total bill and it does not make every supplier charge the same amount.

The applicable rates vary by cap period, region, payment method and meter type. Fixed deals and specialist smart tariffs have their own contract terms. A supplier can therefore offer a fixed deal below today’s cap that later proves dearer than a future default tariff, or vice versa.

Use the current Ofgem tables when comparing against a default tariff. Do not preserve an old national cap figure in a spreadsheet and treat it as the long-term alternative. Model at least:

the rates known today
a reasonable higher-cost case
a reasonable lower-cost case
any exit fee if circumstances change

The purpose is not to forecast wholesale markets perfectly. It is to see whether one decision remains acceptable across plausible outcomes.

Compare time-of-use tariffs with interval data

An off-peak headline is only valuable for electricity that can use it. Calculate how much demand genuinely falls in each band.

For an EV, distinguish between:

a whole-home cheap window, where all household use in the period receives the lower rate
managed or add-on charging, where only qualifying vehicle consumption receives the special price

Check charger and vehicle compatibility, minimum managed-charging requirements, fair-use rules and what happens when the integration fails.

For a battery, include charging and discharging losses, power limits, usable capacity, backup reserve and warranty throughput. A gross difference between the cheap and dear rate is not the net saving.

For a heat pump, use winter-weighted demand and consider whether comfort and hot-water needs can genuinely move into cheaper periods. A tariff that looks attractive on an annual average can perform poorly if its expensive band coincides with the coldest evening hours.

Add export as a separate contract

Solar export is not normally included in a standard import comparison. Calculate it separately from actual or modelled half-hourly export.

Record:

flat, time-of-use or dynamic export rates
whether the export rate requires the same import supplier
whether it is tied to a supplier-installed system
term, rate-change and end-of-term rules
certification, DNO and export-MPAN requirements
treatment of batteries and mixed grid-charged export

Then compare the net annual position:

net energy cost = import cost − export payment

A premium export rate can be poor value if it forces the home onto a materially dearer import tariff. Conversely, the best import deal may still win after accepting a lower open export rate. Test the combination, not the most attractive number on either side.

Compare service using like-for-like evidence

Price matters until a bill is wrong, a meter stops communicating or an export application stalls. Use independent, periodically updated evidence rather than a supplier’s awards page.

Citizens Advice publishes a supplier customer-service comparison using complaints, contact waiting time, billing and whether commitments are met. Ofgem publishes market and supplier service data. Read the reporting period, sample size and method before comparing positions from different tables.

Review sites can reveal recurring problems, but their scores can be affected by invitation methods, complaint campaigns and the types of customers who choose to post. Look for repeated, specific patterns rather than treating a single star rating as an audited performance measure.

Useful questions include:

Can the supplier support the property’s meter type and smart services?
Does it explain missing-data and estimated-bill rules clearly?
Can export, FIT or complex-meter issues reach a specialist team?
Are bills and tariff changes understandable?
What do current complaints data say about resolution, not merely contact speed?

If a complaint remains unresolved after the relevant period or reaches deadlock, the Energy Ombudsman can provide independent dispute resolution. That safety net does not remove the inconvenience of poor service, so it is still a comparison factor.

Check benefits and accessibility before switching

Some household protections and services are supplier-dependent. Before moving, confirm any reliance on:

Warm Home Discount participation and the rules applying in the relevant nation
Priority Services Register support
prepayment features and emergency or friendly-hours credit
accessible bills, nominated contacts or communication needs
repayment plans or debt arrangements

Do not assume that a benefit on the old account automatically transfers in the same form or at the same time. Check the current government or regulator list rather than a copied supplier list, because participants change.

Read renewable claims carefully

Electricity from different generators is mixed on the public network. A “100% renewable” tariff normally refers to matching consumption through Renewable Energy Guarantees of Origin or another procurement arrangement, not a dedicated physical flow to the property.

If the environmental claim affects the decision, ask:

Are certificates bought with the electricity or separately?
Does the supplier have direct power-purchase agreements?
Does it own or fund generation?
Is matching annual, monthly or more granular?
Is gas included in the claim, and if so how?

This allows two similarly labelled green tariffs to be compared on what the supplier actually purchases or supports.

Check the supplier and the contract

Confirm the legal supplier named in the tariff information, not only the consumer brand. One group can operate several brands or licensed entities.

Supplier size and ownership are context, not a guarantee of future stability. If a domestic supplier fails, Ofgem’s Supplier of Last Resort process protects continuity of supply and deals with credit balances under the appointed arrangement. It can still produce a tariff change and administrative delay.

Before accepting a quote, save:

tariff information and prices
contract terms and privacy notice
promised start date
opening meter readings and photographs
exit-fee and cooling-off terms
evidence of any promised credit, reward or export rate

Web pages change. The documents accepted at sign-up are the best record of what was agreed.

Switching checklist

Before the switch:

Calculate the old and new whole-year cost on the same usage.
Subtract any exit fee and include any loss of export or other benefit.
Check meter, EV, battery and export compatibility.
Confirm the effective date and cooling-off arrangements.
Download bills, interval data and account statements from the old supplier.

At the changeover, take dated meter readings and keep the new supplier’s acknowledgement. Check the first bill against the agreed rates, standing charge, opening reading and tariff start date.

If the switch is delayed, made in error or produces an incorrect final bill, use the supplier’s complaint process and current Ofgem guidance on automatic compensation. Exact compensation amounts and deadlines can change, so the live regulator page is more reliable than a static article.