Fixed vs flexible business energy contracts: pros, cons, when to use each

For most UK SMEs, the energy contract decision starts and ends with a single question: fixed or flexible? Get this right and you set the framework for every renewal that follows. Get it wrong and you either pay for complexity you do not need, or accept volatility you cannot afford.

This guide breaks down what each contract type actually does, when each one makes sense, and the volume thresholds at which the conversation shifts.

Fixed-price contracts: the SME default

A fixed-price contract locks unit rates (pence per kWh) and standing charges (pence per day) for a defined term, typically 12, 24, 36 or 48 months. Pass-through items (CCL, RO, CfD, FiT, TNUoS, BSUoS) usually float with whatever rate is in force when the unit is consumed.

What you get with fixed

• Full budget certainty on the largest line items of your bill.
• Simple monthly invoicing, easy to validate and forecast.
• Zero management overhead. Sign, file, monitor.
• Protection against wholesale spikes during the contract term.

What you give up with fixed

• The supplier prices in a risk premium for taking the wholesale risk on your behalf. In normal markets this premium is small. In volatile markets it can be significant.
• No upside if wholesale prices fall during your term. You are locked in at the rate you signed.
• One-shot procurement risk: if you sign at the top of the wholesale cycle, you wear that pricing for 24-48 months.

For a UK SME on stable usage with under 1 GWh annual consumption, fixed is almost always the right answer. The wholesale spread you could capture with flex usually does not cover the management overhead and basket admin.

Flexible (flex) contracts: scale procurement

A flex contract lets you buy your energy in tranches over a defined buying window, usually 12 to 24 months long. Instead of one big procurement decision, you make many smaller ones, hedging against wholesale spikes by spreading your buying across time.

Most flex contracts are structured as a "click" buying window: you (or your appointed procurement manager) execute purchases of volume at moments of your choosing, against pre-agreed market triggers or simply on judgment.

The three main flex structures

What you gain with flex

• Direct exposure to wholesale prices, with no supplier risk premium.
• The ability to capture wholesale lows by clicking on dips.
• Spread procurement risk across time rather than betting on one signing moment.
• Sophisticated price hedging through partial fixes and structured products.

What you take on with flex

• Active management cost. Someone has to watch the market and make click decisions.
• Basket admin: monthly reconciliation, settlement against wholesale curves, more complex invoicing.
• The risk of clicking badly. If you buy all your tranches at the wrong moments, you can end up paying more than a fixed contract would have cost.
• Steeper learning curve. The first 6 to 12 months of any flex contract are about getting the discipline right.

Where the threshold sits

The honest answer: around 1 GWh annual consumption is where flex starts to be a serious conversation. Below that, fixed wins on simplicity. Between 1 and 3 GWh, the case is mixed and depends heavily on your sector, baseload stability, and management capacity. Above 3 GWh, flex usually wins on long-term economics if executed well.

Multi-site portfolios complicate this. A group with 12 sites totalling 4 GWh is a flex candidate. A single site at 4 GWh is even more so. We model both scenarios for clients in this zone before recommending.

Click strategies: the discipline that makes flex work

The single biggest determinant of flex contract outcomes is whether you have a click strategy. A click strategy is a pre-agreed set of rules governing when you will buy tranches.

Examples:

• Trigger-based: buy a tranche each time wholesale falls below a defined threshold.
• Time-based: buy equal tranches at fixed monthly intervals across the buying window.
• Hybrid: a baseline time-based schedule with bonus tranches at defined market signals.
• Stop-loss: if wholesale rises above a defined threshold, buy immediately to prevent further exposure.

The strategy exists to remove emotion from the buying decision. Click decisions made in the heat of a market move are usually worse than click decisions made against a pre-agreed framework. Even if the framework is imperfect, the discipline matters.

What the decision actually looks like in practice

For a 400,000 kWh/year retail group, the answer is fixed. The volume does not justify flex overhead.

For a 6 GWh/year cold storage operator, the answer is flex with a click strategy. The wholesale spread you can capture across a 24-month buying window outweighs the management cost.

For a 25-site care home group totalling 8 GWh, the answer is usually basket flex through a broker-managed basket, which gives scale benefits without each site needing to manage its own buying.

Who decides when you click

On any flex contract, click authority sits with three possible parties:

• You (the business): full control, full responsibility. Right for businesses with internal energy procurement expertise.
• Your broker: we recommend click points, you sign off. Most common arrangement for SMEs in the 1-3 GWh band.
• A delegated procurement manager: full authority to execute against the agreed strategy without per-click sign-off. Used by larger organisations or basket structures.

The bottom line

Fixed-price contracts are the right answer for the overwhelming majority of UK SMEs. They are simple, predictable, and remove a class of risk you do not need to manage.

Flex contracts are powerful tools when the volume, sector profile, and management capacity justify them. They are not the right answer just because someone has sold you complexity.

If you are unsure where you sit, the honest test is: do you have 1 GWh+ annual consumption AND someone with the time to engage with monthly procurement decisions? If yes to both, flex is on the table. If no to either, fixed is the right call.