Variable-Rate Contract
What is a variable-rate energy contract?
If you’ve ever opened a renewal letter and seen your unit rate jump 30% overnight, you’ve felt the downside of a variable-rate contract. They’re the opposite of a fixed deal in one important respect. The rate you pay this month isn’t guaranteed to be the rate you pay next month. For some businesses that flexibility is useful. For most it’s a budgeting headache.
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Variable-rate contracts in the UK business energy market sit at one end of a spectrum that runs from fully fixed at the other. Choosing between them isn’t really about price. It’s about how you want to manage risk.
What a variable-rate contract actually is
In a variable-rate contract your unit rate isn’t locked. The supplier sets the rate, but they retain the right to change it during the contract term. Notice periods vary. Some suppliers commit to 30 days’ notice, others as little as a week.
The rate can move up or down. In practice, most variable rates move up. Suppliers face wholesale market volatility on the buying side, and a variable contract gives them the freedom to pass that volatility through.
Contracts of this shape are not the same as out-of-contract rates, though they can look similar at a glance. An OOC rate is what you fall onto when a fixed contract ends without a renewal. A variable-rate contract is an active agreement you’ve signed up to.
How rates change
There’s no single mechanism. Different suppliers use different triggers:
- Index-linked. Some variable contracts track a published wholesale index. Typically a day-ahead or month-ahead reference rate. When the index moves, your rate moves with it on a fixed lag.
- Supplier-set. Others give the supplier discretion to set the rate as they see fit, with a contractual notice period before each change.
- Hybrid. Some contracts fix one component (often standing charges) and float the unit rate, or vice versa.
If you’re on a supplier-set variable, the contract is closer to a rolling arrangement than to anything market-linked. The supplier picks the rate, gives notice, and changes it.
Variable-rate vs fixed-rate
The fundamental difference is risk allocation.
A fixed-rate contract says. The supplier takes the wholesale risk, and you pay a premium for that certainty. Whether wholesale prices go up or down during your term, your rate stays the same.
A variable-rate contract says. You take the wholesale risk, and you pay a lower starting rate in exchange. Whether wholesale prices go up or down, your rate moves with them.
The lower starting rate on a variable can be significant. Sometimes 10 to 15% below the equivalent fixed quote. But that gap can vanish in a single month if wholesale prices spike, as happened repeatedly through 2021 and 2022.
When variable-rate makes sense
There are a few situations where a variable contract is a sensible choice:
- Short bridging periods. If you know you’re going to switch supplier in two months but need cover in the meantime, a variable rate can be cheaper than locking in a year-long fixed.
- Falling wholesale markets. If you genuinely believe wholesale prices will fall during your term, a variable rate captures the downside that a fixed doesn’t.
- High-volume, sophisticated buyers. Businesses with someone watching the market daily can ride a variable rate and switch to fixed at the right moment. This is closer to flexible procurement than a typical SME variable contract.
- Energy-intensive sites with hedging strategies. Large industrial users sometimes pair variable supply contracts with their own financial hedges.
For most UK SMEs, none of these apply.
When it does not make sense
Variable contracts are usually a bad fit if:
- Your business needs predictable monthly costs for budgeting or board reporting.
- You’re a tight-margin operator where a 30% jump in energy costs would hurt.
- You’re a microbusiness without the bandwidth to monitor markets weekly.
- You’re on a long enough term that the rate could move multiple times before you can exit.
For most small and mid-sized businesses, a 12 or 24-month fixed contract is the lower-headache option. The premium you pay for fixing is the cost of removing volatility from your budget.
Common variable-rate structures
You’ll typically see one of these structures on offer:
- Pure variable. Supplier sets the rate, gives notice when it changes. Most flexible, most uncertain.
- Wholesale-tracking variable. Rate moves with a published wholesale index on a fixed lag. More transparent, but still exposed to wholesale volatility.
- Capped variable. Variable rate with a price ceiling and sometimes a floor. The cap protects you from spikes; the floor protects the supplier.
- Pass-through. The energy component floats but non-commodity costs are fixed. Different from a full pass-through contract, which floats the other way around.
The further you go from pure variable, the closer you get to a fixed contract in effect.
Switching out of a variable rate
One genuine advantage of a variable contract is exit flexibility. They typically come without an early-exit fee. You can give notice and switch to a fixed contract or another supplier, usually with 30 days’ notice.
That contrasts with a fixed contract, where leaving mid-term usually triggers an exit fee equal to the supplier’s lost margin.
If you’re sitting on a variable rate that’s just gone up sharply, the path out is the same path in. Get a fresh quote on a fixed deal, agree the switch date, and serve notice on the variable. Time the switch around the renewal anniversary or quarter end to keep the transition clean.
This is also where bill validation matters. Variable contracts produce billing inconsistencies that fixed contracts don’t, simply because rates change. Catching errors early saves money.
Common pitfalls
A few things that catch businesses out on variable contracts:
- Sleepwalking past a renewal. Variable contracts don’t end on a fixed date the way fixed contracts do. It’s easy to stay on one for years without ever reviewing.
- Notice misunderstandings. Some variable contracts require notice in writing within a tight window. Miss it, and the contract auto-rolls.
- Hidden uplift on renewal. Suppliers sometimes apply a step change at the contract anniversary that doesn’t track wholesale at all. Reading the renewal letter carefully matters.
- Conflating variable with deemed. If you let a fixed contract lapse, you fall onto deemed or out-of-contract rates, which are usually higher than even a generous variable rate.
- Term mismatches. Some variables run for fixed terms; others are evergreen. Check which yours is.
The rule of thumb. If you’re on a variable and you haven’t reviewed it in the last six months, it’s probably worth a fresh look.
Frequently asked questions
What is a variable-rate energy contract?
A business energy contract where the unit rate is not locked for the term and can be changed by the supplier during the contract, usually with notice. The rate can move up or down in response to wholesale market changes or supplier-set adjustments.
How is a variable-rate contract different from a fixed-rate?
A fixed-rate contract locks the unit rate for the term. The supplier takes the wholesale market risk. A variable-rate contract leaves the unit rate exposed to changes, so the customer takes the wholesale risk in exchange for a typically lower starting rate.
How often does the rate change on a variable contract?
It depends on the contract. Some change monthly with a published wholesale index, others change only when the supplier decides to revise the rate with notice. Notice periods range from one week to 30 days.
Is a variable-rate contract cheaper than fixed?
The starting rate is usually lower, sometimes 10 to 15% below the equivalent fixed quote. Whether it stays cheaper across the term depends on what wholesale prices do. In volatile markets variable contracts can end up significantly more expensive.
Can I leave a variable-rate contract early?
Usually yes, with notice. Most variable contracts do not have early-exit fees, unlike fixed contracts. Notice periods are typically 30 days.
What is the difference between variable-rate and out-of-contract rates?
A variable-rate contract is an active agreement you have signed up to. Out-of-contract rates are what you fall onto when a fixed contract ends without a new contract in place. OOC rates are typically much higher than variable rates.
When does a variable-rate contract make sense?
For short bridging periods between contracts, when wholesale prices are clearly falling, or for sophisticated buyers who actively monitor markets and switch to fixed at the right moment. Most small and mid-sized businesses are better off on a fixed contract.
What is a capped variable contract?
A variable-rate contract with a price ceiling that limits how high the rate can go, and sometimes a floor that limits how low. The cap protects against spikes; the floor protects the supplier from low markets.
Will my standing charge change on a variable contract?
Depends on the contract. Pure variable contracts can adjust standing charges with notice. Some structures fix the standing charge and only float the unit rate. Read the contract carefully.
How do I switch from variable to fixed?
Get a quote on a fixed contract, agree the switch date, and serve notice on the variable contract. Notice periods are typically 30 days. Time the switch around the contract anniversary or quarter end for a clean transition.
Do small businesses ever benefit from variable rates?
Occasionally, but it requires actively monitoring wholesale prices. Most small businesses do not have the bandwidth for that and end up paying more on a variable contract than they would have on a fixed deal.
Can a supplier increase my variable rate without notice?
No. UK regulations require a minimum notice period before a variable rate increase, usually 30 days for protected customers and 7 to 14 days for larger businesses. Check your contract terms for the exact notice obligation.