When and how to switch energy tariff in the UK

Energy is most households' largest recurring bill after rent or the mortgage, and it is also the one people are most passive about. Unlike a streaming subscription, you cannot simply cancel gas and electricity — but you can switch tariff or supplier, and the difference between a good deal and a default one is regularly hundreds of pounds a year. This guide explains how the UK market works right now and exactly how to switch safely.

1. Know your current deal first

Before switching, you need two numbers from your latest bill or your supplier's app: your tariff name, and your annual usage in kilowatt-hours (kWh) — not your monthly cost in pounds, which swings with the seasons. Usage is what makes quotes comparable. If you do not have it, an estimate based on your household size will do for a rough comparison, but the real figure is always better.

Also note whether you are on a fixed tariff (a set unit price for a fixed period) or a variable one (a price that follows the market, capped by Ofgem). The decision to switch depends entirely on which of those you are on.

2. Fixed vs variable, in plain English

A fixed tariff locks your unit price and standing charge for a set term — typically 12 or 24 months. Your bills still go up in winter because you use more, but the price per unit stays put. The risk is that if wholesale prices fall, you are stuck paying the higher fixed rate until the term ends, unless you pay an exit fee.

A variable tariff moves with the market and is governed by the Ofgem price cap, which sets the maximum a supplier can charge per unit. When the cap falls, your bills fall automatically. The cap updates every three months, so a variable deal is the safer choice when prices are trending down and you do not want to be locked in.

As a rule of thumb: fix when you want certainty and prices are expected to rise; stay variable when prices are falling or uncertain and you value flexibility. There is no universally “correct” answer — it depends on your appetite for bill surprises.

3. When your fixed deal ends, act fast

This is the moment most people lose money. When a fixed tariff ends, suppliers roll you onto their standard variable tariff by default — which is rarely their cheapest option. Your supplier must tell you the new tariff around 42 to 49 days before the switch happens. That window is your cue to shop around. If you do nothing, you will almost certainly pay more than you need to.

Put the end date in your calendar the day you sign up. Treat it exactly like a subscription renewal — because it is one.

4. How to compare properly

Use a comparison service that quotes based on your actual kWh usage, not just your postcode and household size. Look at the projected annual cost, not the headline discount — suppliers can make a tariff look cheap by lowering the standing charge and raising the unit rate, or vice versa, so the only honest number is the total for your real usage.

Check the exit fee. A tariff with a fee is not automatically worse, but if you think you might move house or switch again within the term, a no-exit-fee variable deal gives you the optionality for free.

5. The switching process, step by step

• Get a quote based on your annual kWh usage and your current tariff.
• Confirm there is no exit fee that would wipe out the saving, or that you are happy to pay it.
• Sign up with the new supplier. They handle the switch — you do not need to contact your old supplier.
• Take a meter reading on the day of the switch so neither supplier estimates it.
• Pay your final bill from the old supplier and close any direct debit once it is settled.

The whole switch takes about two to three weeks, your supply does not interrupt, and the pipes and wires are exactly the same — only who bills you changes.

6. Help you might be missing

If you receive certain benefits or are on a low income, you may qualify for the Warm Home Discount — a one-off credit on your winter bill. Eligible households also have access to priority services registers and, in some areas, free or subsidised insulation. These rarely arrive automatically; it is worth checking eligibility every autumn.

Tracking energy alongside your other recurring bills — rather than as a separate, ignore-it-until-it-arrives cost — is what turns a once-a-year panic into a quiet annual habit. SubCentral lets you record your tariff, renewal date and cost next to everything else, so the switch window never passes you by.