The number everyone is quoting
On 31 March 2026, Cornwall Insight published its latest forecast for the July to September price cap: £1,929 for a typical dual-fuel household. That is an increase of £288, or 18%, on the current April cap of £1,641. EDF's weekly forecast stood at £1,937; E.ON at £1,955. The driver is the Middle East conflict that has disrupted LNG supply routes and sent European wholesale gas prices sharply higher.
The response was immediate. Prime Minister Starmer chaired a COBRA meeting. The £1,641 cap, already locked in for three more months, was cited as an act of government protection. Rachel Reeves signalled that targeted support for vulnerable households was being considered if autumn bills rose. Energy minister Martin McCluskey said: "If it's necessary to intervene, we will." And the news cycle filled with £300 bill rises, warnings about fuel poverty, and calls for a social tariff.
All of that political activity is directed at a number, £1,929, applied to a quarter when the average British household burns through barely a tenth of its annual gas consumption. The coverage is not wrong about the forecast. It is largely silent on what the forecast actually means in practice for a summer energy bill.
Why Q3 is the wrong quarter to panic about
The Ofgem price cap is expressed as an annual equivalent figure for a household consuming the Typical Domestic Consumption Values: 2,700 kWh of electricity and 11,500 kWh of gas per year. It is not a bill. Your actual quarterly spend depends on how much energy you use in those three months, and that varies enormously by season.
Ofgem's own demand-weighting methodology, used in setting the cap, tells you exactly how gas consumption is distributed across the year:
Source: Ofgem price cap methodology (Annex 2). Q3 is 11% by consumption volume. By cost, because wholesale gas is cheaper in summer, the effective cost-weighted share is closer to 8-9%.
Q3 is the lowest demand quarter by a significant margin. A household that uses 11,500 kWh of gas per year uses approximately 1,265 kWh in July to September, less than any other quarter, and roughly a third of what the same household burns in Q1.
That changes the arithmetic of a higher cap substantially. Here is what a Q3 cap of £1,929 actually costs in additional gas spend compared to the current £1,641 cap, for the 91 days of summer:
| Quarter | Cap level | Gas unit rate | Q3 gas consumption | Q3 gas bill | Standing charge (91 days) | Total Q3 gas cost |
|---|---|---|---|---|---|---|
| Q2 2026 (current) | £1,641 | 5.74p/kWh | ~1,265 kWh | ~£73 | ~£26 (29p/day) | ~£99 |
| Q3 2026 (forecast) | ~£1,929 | ~7.3p/kWh* | ~1,265 kWh | ~£92 | ~£26 (unchanged) | ~£118 |
| Difference | +£288/yr equivalent | +~1.56p/kWh | - | +£19 | - | +~£24 over the quarter |
*Estimated gas unit rate at £1,929 cap based on proportional scaling. Standing charges may also change at the Q3 announcement. Electricity costs not included above - electricity seasonal variation is smaller (summer ~46%, winter ~54% of annual). TDCV: 11,500 kWh gas/year, 91-day quarter. Figures are illustrative.
In plain terms: a typical household on a default tariff will pay roughly £24 more in gas costs over the three months of summer at the forecast Q3 cap than they are paying now. That is the real-world difference between £1,641 and £1,929 expressed as what lands on a July to September bill, not £288, which is an annualised equivalent applied to typical full-year consumption. The annualised figure is not wrong, but it is not your summer bill either.
The electricity side adds a little more. Electricity demand is less seasonal than gas, around 46% falls in summer and 54% in winter, and the electricity unit rate would also rise at a higher cap. But the overall direction is the same: a Q3 cap rise is materially less painful than an equivalent Q4 or Q1 rise, because households simply use less energy in summer.
Q4 is the quarter that actually matters
This is the part of the story that has been almost entirely absent from the coverage, and it is the part the government clearly understands even if it is not saying it out loud.
The Q4 cap, covering October, November and December, is set by Ofgem using a separate observation window that closes in mid-August, with the announcement due by 26 August 2026. The Q4 assessment period runs later than Q3's, meaning it will capture wholesale gas prices through the summer. If the Iran conflict de-escalates, if the Strait of Hormuz reopens, if European storage refills ahead of schedule, all of that would feed directly into a lower Q4 cap.
Q4 is when UK households use 32% of their annual gas. It is the quarter when heating comes back on, bills double, and fuel poverty bites. A £288 annual equivalent rise landing in Q4, 3,680 kWh of gas consumed rather than 1,265 kWh, would cost a household roughly £75-80 more in actual gas spend over three months, not £24. That is a materially different conversation.
The key asymmetry: The political alarm is calibrated to Q3, the quarter where the real-money impact of a higher cap is smallest. The question everyone should be asking is what Q4 looks like. That depends almost entirely on what happens to wholesale gas prices between now and mid-August. Nobody knows. And notably, no government spokesperson has committed to any specific intervention threshold for autumn.
The observation window: what has to happen for Q4 to be different
Understanding how the cap is actually calculated helps clarify what households should be watching rather than reacting to.
NowQ2 cap locked until 30 June
Your bills cannot rise before 1 July regardless of what happens in wholesale markets. The £1,641 cap is legislatively fixed for the quarter.
Closes 17 MayQ3 observation window ends
The wholesale prices that determine the July to September cap are being averaged across a window from 18 February to 17 May 2026. Prices since late February have been elevated due to the conflict. Whatever the average looks like on 17 May is roughly what Ofgem will use for the Q3 cap calculation.
By 27 MayQ3 cap announced
Ofgem must publish the Q3 cap level by 27 May. This will be the confirmed, not forecast, figure. If the conflict stabilises before 17 May, the final number could come in below current analyst forecasts. If it escalates, it could be higher.
Jun-AugThe Q4 window, the one that counts
The observation period for the October to December cap runs separately and includes summer months. This is where market cooling, if the geopolitical situation improves, would actually show up in the cap. A ceasefire, a reopening of the Strait of Hormuz, European storage refilling to strong levels: any of these could bring Q4 forecasts down materially from where Q3 currently sits.
26 AugQ4 cap announced, the political moment
This is when the autumn energy bill picture becomes clear. If Q4 is high, the government faces a genuinely difficult political and fiscal decision about intervention. If wholesale prices have eased through summer, the problem may have largely resolved itself. There are roughly four months of market data between today and the Q4 announcement that remain completely unknown.
What the government has actually committed to
The political messaging since the Iran conflict began has been carefully calibrated to project action without committing to specific support. It is worth being precise about what has and has not been announced.
Already in place
- £1,641 Q2 cap locked until 30 June - saving £117/yr vs Q1 level
- £53 million Crisis & Resilience Fund for heating oil customers (not on mains gas)
- Fuel duty cut extended to September 2026
- Warm Home Discount: £150 to ~6 million eligible households this winter - continuing annually
- Legal direction to suppliers to pass through ECO/RO removal savings in full
- "Cheap Fuel Finder" app for forecourt price transparency
Signalled but unconfirmed
- Targeted support for vulnerable households if autumn bills rise - Reeves: "if necessary"
- Fuel duty September rise under review - Starmer: "monitoring in light of Iran"
- Further intervention if Q4 cap rises sharply - Miliband: "if necessary to intervene, we will"
- Social tariff for energy - long-discussed, no mechanism or timeline committed
- Winter fuel payment reinstatement or expansion - not committed
The pattern is consistent: everything announced is either already legislated or costs relatively little. Everything that would address a materially higher Q4 cap, a new price guarantee, targeted bill support, an expanded Warm Home Discount, is conditional on circumstances that have not yet materialised. That is not necessarily wrong. The government would be right not to commit now to expensive intervention for a quarter that may not need it. But it is worth being clear that the current political response is not the autumn safety net, it is the holding position while the market plays out.
The 2022 precedent: why timing matters
The last time the UK government intervened at scale on energy bills, the Energy Price Guarantee introduced in October 2022, it was announced in September, covering a Q4 cap that without intervention would have been £4,279 for a typical household. The government stepped in with a £2,500 equivalent cap and the Treasury absorbed the difference.
That intervention was politically and economically significant, costing the government an estimated £25 billion over six months. It was also effective: households were protected during the highest-cost quarter of the year, when gas consumption is highest and vulnerable households most at risk.
The structural lesson is that interventions calibrated to October, when Q4 gas consumption is ramping up, have far more real-money impact per pound spent than those calibrated to July. This is presumably why Rachel Reeves is signalling autumn rather than summer support. A £288 annual equivalent rise in Q3 costs the average household about £24 extra over the quarter. The same rise in Q4 would cost around £75-80 extra. The intervention calculus is very different.
The question politicians aren't answering yet: At what Q4 cap level would the government intervene, and what form would that take? The "if necessary" language is deliberate ambiguity, designed to signal concern without triggering market speculation, fixed-deal panic, or spending commitments that may prove unnecessary if wholesale prices ease. It also avoids setting a threshold that suppliers and analysts would immediately start trading against. This is the right political strategy for now. It will become an insufficient answer if Q4 comes in above £2,000.
What to watch over the next four months
The narrative around energy bills will be set in August, not now. The variables that matter are not particularly amenable to government influence in the short term, which is another reason the political response has been cautious.
- Strait of Hormuz status. Iran's threat to close the strait is the proximate cause of current price levels. Any indication that shipping routes are reopening would immediately move futures markets, and therefore the Q4 observation window, lower.
- European gas storage fill rate. Storage entering the injection season (April to September) is the key buffer against winter shortages. If storage fills strongly through summer, forward prices for Q1 2027 ease, which also drags Q4 2026 prices lower as market participants reprice tail risk.
- Q3 cap confirmation on 27 May. The actual number from Ofgem, rather than analyst forecasts, matters both practically and politically. If it comes in below £1,929, the pressure eases slightly. If it comes in above, the Q4 discussion intensifies earlier.
- Fixed deal pricing. What suppliers are willing to offer on fixed deals is a real-time signal of where they expect prices to go. If well-priced fixed deals return at £1,700-1,800 levels, that implies the market sees Q4 cooling. If they stay above £2,000 or disappear entirely, that implies sustained elevated prices.
- US-Iran diplomatic track. US President Trump's threats to obliterate Iranian infrastructure alongside simultaneous claims of "great progress" in negotiations are creating unusual uncertainty. A diplomatic resolution, even a partial one that allows some shipping, could move prices significantly in a short window.
The bottom line
The £288 forecast rise for Q3 is real, based on credible methodology, and reflects a genuine supply disruption. It should not be dismissed. But it should be understood for what it is: an annualised headline applied to the three months when British households use the least energy of the year. The practical cost of that rise in your actual summer bill is around £24 in extra gas spend over the quarter, less than a takeaway, rather than the headline number suggests.
The political alarm and the government's holding position are both rational given that Q4 is unresolved. The four months between now and the 26 August announcement are the period that matters. If the conflict eases and markets cool, the problem may resolve without the intervention that analysts and civil society groups are already calling for. If it does not, the government will face a much harder conversation, and a much larger bill, in September.
Watch the Q3 announcement on 27 May for the first real signal of where Q4 is heading. Until then, the £300 rise is a forecast, not a fact, applied to the quarter when it matters least.