Will the UK’s 2026 inflation be between 3.5% and 3.9%?

- [2026-09-16] ONS released August 2026 CPI data: the Consumer Prices Index (CPI) rose by 3.1% in the 12 months to August 2026, up from 2.9% the previous month , with CPIH at 3.3% and core CPI unchanged at 2.6%. Source: https://www.ons.gov.uk/economy/inflationandpriceindices/bulletins/consumerpriceinflation/august2026 - [2026-09-16] The August rise was driven mainly by transport: the largest upward contribution came from transport, particularly motor fuels, with prices in the transport division rising overall by 4.6% in the 12 months to August 2026, up from 3.6% the previous month . Overall motor fuel prices rose 23.0% y/y, the fastest pace since the price surge began. Source: https://www.ons.gov.uk/economy/inflationandpriceindices/bulletins/consumerpriceinflation/august2026 - [2026-09-16] Food inflation remains subdued: the 12-month inflation rate for food and non-alcoholic beverages was 1.3% in August 2026, unchanged from July , providing some offset to energy-driven pressure. Source: ONS August 2026 bulletin. - [2026-09-18] Bank of England's latest published estimate (from MPC minutes around 18 September 2026) shows the near-term path worsening: the Bank of England expects inflation to increase to around 3.75% in the fourth quarter of 2026, according to their latest estimates from 18 September , driven by energy costs including a higher Ofgem price cap. Source: https://moneyweek.com/economy/inflation/inflation-forecast-where-are-prices-heading-next - [2026-09-18] The MPC minutes stated "Based on energy prices as at close of business on 14 September, the direct contribution of energy prices to inflation was expected to increase over coming quarters... Ofgem's headline energy price cap for October to December would be increased to £1,723... and the cap was now expected to rise substantially further in 2027 Q1" . Source: MoneyWeek citing BoE MPC minutes. - [2026-09-17] At its September MPC meeting the Bank held the base rate at 3.75% on 17 September 2026, with a 6-3 vote (Greene, Mann and Pill voting for a rise to 4%), and said inflation risks have moved further to the upside . Source: https://www.xtb.com/en/education/uk-interest-rate-forecast - [2026-09-25/26] Commons Library indicators page (updated with August data) notes the conflict in the Middle East and the associated rise in energy prices is expected to lead to higher UK inflation; prior to the conflict the CPI annual inflation rate was expected to fall to around 2% from April and remain around 2% for the rest of 2026 . Source: https://commonslibrary.parliament.uk/research-briefings/sn02792/ - [2026-08-19] Treasury's monthly survey of independent economists (published 19 August 2026) shows the average forecast from economists surveyed by the Treasury on 19 August is that inflation will rise to 3.4% in the final quarter of 2026 , with a further easing to 2.3% by Q4 2027. Source: MoneyWeek. - [2026-07-30] Bank of England's July Monetary Policy Report (its most recent full quarterly projection prior to the September update) had the Bank of England's central projection showing CPI inflation peaking at around 3.2% in 2026 Q4 , though risks were "tilted to the upside" and oil/gas prices have risen since. Source: House of Commons Library / BoE July 2026 MPR. - [2026-09-19] BCIS (construction cost forecaster) sees the Bank of England expecting inflation to reach 3.75% by the end of the year, suggesting strong upside risk on inflation in the near term, while BCIS itself forecasts inflation to surpass 3.4% by the end of the year and potentially reach 4% by December . Source: https://www.bcis.co.uk/news/latest-economic-forecasts/ - [2026-09-16] The next ONS release (September 2026 data) is scheduled for 21 October 2026, and December 2026 data (the resolution month) is scheduled for release on 20 January 2027, per the ONS release calendar referenced in the market rules. Source: https://www.ons.gov.uk/economy/inflationandpriceindices/bulletins/consumerpriceinflation/august2026 (next release note) and https://www.ons.gov.uk/releases/consumerpriceinflationukseptember2026 - [2026-09-25] Nowflation/Treasury-style trackers of UK path are less common than for US CPI, but UK-specific commentary (MoneyWeek, 22 Sept 2026) states soaring energy and motor fuel prices are pushing inflation up, with the Bank of England now predicting price growth could reach 4% next year , underscoring upside momentum into Q4. Source: https://moneyweek.com/economy/inflation/inflation-forecast-where-are-prices-heading-next BOTTOM LINE: As of the latest published data (August 2026, CPI 3.1% y/y, rising for a second straight month largely on motor-fuel and energy costs), both the Bank of England (≈3.75% Q4 central case per its September update, versus 3.2% in its July MPR) and independent economists (Treasury panel average 3.4% for Q4) point to headline CPI climbing further into the autumn before the December print, putting the 3.5–3.9% band plausibly in play but not a settled outcome; some forecasters (BCIS) see risk of a print near or above 4%, while others (Treasury panel average) sit just below the band at 3.4%. NOT FOUND: No September 2026 CPI figure exists yet (release due 21 October 2026); no October, November or December 2026 CPI data exist yet since those months have not been measured/published; no official ONS or BoE point forecast specifically for the December 2026 y/y CPI print (only Q4-average/peak estimates) was found.

**Reference class & base rates** - [2026-09-17] Based on energy prices as at close of business on 14 September, CPI inflation was expected to increase to around 3¾% in 2026 Q4, compared with 3.2% at the time of the July Report, and to reach slightly above 4% in 2027 Q1. Source: Bank of England September 2026 MPC minutes. - [2026-07-30] CPI inflation is expected to average 3.2% in 2026 Q4. The near-term CPI inflation projection rises to 3.2% in October and November 2026 before easing a little. This shows the BoE's own central forecast moved up ~0.55pp in just two months (July→September MPR cycle), illustrating how quickly point forecasts for this exact window have shifted. - [2026-08-19] The average forecast from economists surveyed by the Treasury on 19 August is that inflation will rise to 3.4% in the final quarter of 2026. By Q4 2027, they expect inflation ease to an average of 2.3%. - [2026-09-21] Bank of England now predicting price growth could reach 4% next year , with Deutsche Bank's chief UK economist expecting CPI on course to get close to 4% around the turn of the year . - [2026-09-26] Third-party algorithmic forecast site poundf.co.uk projects CPI forecast for December 2026: the forecast for the beginning of December 3.78%, maximum rate 3.81%, minimum 3.37%, average interest rate for the month 3.64%, inflation at the end 3.59%, change for December -0.19 points — i.e., a point estimate clustering around 3.5–3.8%, squarely inside or just above the question's 3.5-3.9% band. - [2026-09-25] Actual outturn as of the latest official data: UK inflation rose almost continuously from under 1% in early 2021 to 11.1% in October 2022, a 41-year high, before easing over the following two years; prior to the conflict the CPI annual inflation rate was expected to fall to around 2% from April and remain around 2% for the rest of 2026 — showing the current above-target trajectory is a deviation from the pre-shock base case, driven by an exogenous (Middle East conflict/energy) shock rather than a "normal" disinflation path. - [2026-08-19] Latest hard data point: the change in the annual rate, from 3.1% to 3.3% (CPIH) between July and August 2026, with headline CPI at 3.1 percent in August 2026, up from the previous month when it was 2.9 percent . **Track record of forecasts (BoE and professional forecasters) as a base rate for hitting a narrow 0.4pp band** - [2025-10-08] Academic post-mortem on 2021-24: The Bank of England badly mis-forecast UK annual consumer price inflation as it rose rapidly from 2021, prompting a review by Ben Bernanke... Unpredictable shocks explain some of the bank's forecast failures, but tardy reactions also mattered. This underlines that during shock periods (like the current energy/Middle-East shock), forecast errors of well over 1pp have historically occurred, which is much larger than the 0.4pp width of this market's target band. - [2025-xx] Broader academic literature notes the forecast errors made by the Bank of England and those made by external forecasters are barely distinguishable... forecasters make similar mistakes, highlighting the significant role of judgment in the forecasting process , meaning neither BoE nor consensus economists should be treated as unusually precise, especially amid an active geopolitical/energy shock. - [2024-04-15] Bernanke review found the Bank of appearing to "at times suffer from excessive incrementalism," he said policymakers had raised rates slowly over the past two years when inflation was already rising beyond normal levels , reinforcing that BoE/consensus forecasts tend to underreact to emerging shocks — a relevant caution given the current energy-driven upswing. **Directional consistency across forecasters** - Multiple independent sources (BoE, Treasury-surveyed panel, Deutsche Bank, algorithmic trackers) all currently point to Q4/December 2026 CPI landing somewhere in the high-3s to low-4s, i.e., mostly at or above the top of the 3.5–3.9% band rather than below it, with several explicitly flagging a "close to 4%" risk by year-end/turn of 2027 (see MoneyWeek/BoE/Deutsche Bank citations above). BOTTOM LINE: Historically, BoE and consensus economist forecasts for UK inflation several months out have shown large errors (often >1pp) during shock periods, and the current energy/Middle-East-driven shock is exactly such a period — recent BoE and Treasury-panel forecasts for Q4 2026 cluster around 3.4%–3.8% with a rising trajectory into 2027 Q1 (~4%+), suggesting the true outcome could plausibly land either inside or above the 3.5–3.9% band, with meaningful risk of an upside miss beyond 3.9% given the demonstrated historical tendency of these forecasts to underestimate emerging inflationary shocks. NOT FOUND: No direct Polymarket-specific odds/historical resolution data for this or similar past markets could be located; no OBR-specific December-2026 point forecast (as opposed to full-year average) was found; no formal probability distribution/fan chart percentile breakdown from the September 2026 BoE Monetary Policy Report was accessible in the search results.

**Strongest YES case: BoE's own central Q4 forecast (3.75%) and most independent trackers cluster inside or very near the 3.5–3.9% band, with the mechanism (energy pass-through) traceable and moderating, not runaway.** - [2026-09-21] MoneyWeek's updated explainer quotes the Bank's breakdown that of August's 3.1% inflation rate, around 0.7 percentage points was the direct effect of energy prices, mostly motor fuels , giving a concrete, decomposable mechanism (rather than a vague "energy shock") for how the print could climb toward, but not necessarily beyond, the upper-3s by December. Source: https://moneyweek.com/economy/inflation/inflation-forecast-where-are-prices-heading-next - [2026-09-21] The same piece notes the proximate driver is fuel costs, with soaring energy and motor fuel prices pushing inflation up, and the Bank of England now predicting price growth could reach 4% next year, with its latest estimates from 18 September putting Q4 2026 inflation around 3.75% — i.e., the Bank's own central Q4 case sits almost exactly at the midpoint of the question's 3.5–3.9% band. Source: https://moneyweek.com/economy/inflation/inflation-forecast-where-are-prices-heading-next - [2026-09-21] Petrol is quantified concretely: a litre of petrol now costs around 172p, up almost 40p since the Iran war began (per the article's body), showing the fuel shock, while severe, is a level-shift already largely priced into the annual comparison rather than an accelerating monthly trend — consistent with inflation stabilizing in the high-3s rather than spiralling past 4%. Source: https://moneyweek.com/economy/inflation/inflation-forecast-where-are-prices-heading-next - [2026-08-26] Cornwall Insight — the consultancy Ofgem itself treats as most accurate — forecasts the January–March 2027 price cap at £1,872, only an average January bill up to £1,872 a year, £149 higher than the £1,723 October price cap , i.e. a ~9% rise, materially more moderate than Bloomberg Economics' or EDF's ~25-26% scenarios cited elsewhere. A moderate cap rise supports a Q4 print landing inside rather than above the band. - [2026-09-11] An energy-tariff tracker confirms this 9% figure is the only dated, sourced forecast on the record: The January–March 2027 Ofgem price cap is forecast at £1,872 a year (Cornwall Insight), 9% above October's confirmed £1,723 , reinforcing that the single most credible energy-cost path feeds a mid-3s to high-3s December CPI rather than a blow-out above 4%. Source: https://www.energyplus.co.uk/price-cap/ofgem-january-2027-price-cap-forecast-uk - [2026-09-26] Algorithmic tracker poundf.co.uk's December 2026 projection has the forecast for the beginning of December 3.78%... average interest rate for the month 3.64%... Inflation at the end 3.59%, change for December -0.19 points , an independent, mechanically-generated estimate landing squarely inside the 3.5–3.9% band. Source: https://poundf.co.uk/inflation - [2026-02-16] NIESR's Multi-Recurrent Neural Network (MRN) ensemble — a track record model, not just narrative — found the simple MRN predicts an increase in the January headline to 3.6% from the current level of 3.4%; the Simple with MPC predicts a lower 3.4%; the Simple with DPD a rise to 3.7%... The average of all three is 3.6% , showing independent statistical models (as of their training data) also cluster in the 3.4–3.7% zone near this period. Source: https://niesr.ac.uk/blog/latest-mrn-forecasts-point-higher-expected-inflation-second-half-2026 - [2026-05-18] An earlier NIESR MRN update explicitly benchmarked against the BoE's own scenario planning: the BoE expects inflation to peak just over 3.5 per cent in the final quarter of 2026 before falling back under its Scenarios A/B — a distinct, dated data point showing the Bank's scenario range brackets the low end of the question's band even before the September upgrade to 3.75%. Source: https://niesr.ac.uk/blog/new-modelling-technique-suggests-inflation-could-go-well-beyond-5-cent-early-2027 - [2026-03-05/04-02] Bank of England Decision Maker Panel survey data show UK businesses' own forward-looking inflation expectations running consistent with a mid-3s outcome: UK year-ahead CPI inflation expectations rose to 3.5% in March 2026, up from 3.0% in the previous month , indicating firms — who set prices — were not pricing in a run to 4%+ even as the energy shock began. Source: https://tradingeconomics.com/united-kingdom/dmp-1y-cpi-expectations - [2026-08-19] The Treasury's independent-economist panel — the most policy-relevant "consensus" benchmark — puts Q4 2026 at 3.4%, just below the band's floor but only one-tenth of a point away, and NIESR's July outlook separately has inflation projected to average 3.1% in 2026, up from 2.6% in June with the same report seeing the cycle peaking at 3.8% in February 2027, down from 4.1% in April's forecast — i.e., even NIESR's most recent full-outlook peak estimate (revised down since April) sits inside the band. Source: https://kelo.com/2026/07/28/uks-niesr-nudges-up-growth-forecast-warns-of-persistent-inflation/ - [2026-09-17] The MPC's 6-3 vote to hold rates rather than hike, despite acknowledging inflation risks were now "further to the upside," indicates the median policymaker view is that the current trajectory — consistent with the ~3.75% Q4 central case — does not yet warrant tightening, implying the committee's own base case is not for an inflation blow-out well past 4% by December. Source: https://www.xtb.com/en/education/uk-interest-rate-forecast (background from prior research, cross-checked against MoneyWeek's confirmation of the same 6-3 vote). BOTTOM LINE: The single most likely path to YES is that energy/fuel-driven inflation, which the Bank of England itself now centrally forecasts at ~3.75% for Q4 2026, continues to build through October–December but is capped by a moderate (Cornwall Insight's ~9%, not Bloomberg's ~25%) January price-cap rise; multiple independent trackers (NIESR MRN, poundf.co.uk, Treasury panel, DMP business expectations) cluster in the 3.4–3.8% zone, giving several converging, data-grounded reasons to expect the December print to land inside 3.5–3.9%. NOT FOUND: No forecaster has published a point estimate specifically for the December 2026 y/y CPI print (all cite Q4 averages or peaks); no confirmation yet of the actual Ofgem January 2027 cap (due late November 2026), which is the single largest swing factor for the December print.

- [2026-01-21] The 2025 comparator base already embeds one-off distortions: ONS attributed part of the jump in the rise in the 12-month rate to an upward effect from tobacco, since tobacco duty was increased on 26 November 2025, whereas in 2024 it was increased on 30 October, a timing difference that helps explain why prices fell 0.1% in November 2025 but rose 3.0% in December 2025 . Since 2026's equivalent one-off tobacco/vape duty rise takes effect on 1 October 2026 rather than in November (https://euvape.com/news/uk-budget-tobacco-vape-tax-hike/; https://www.tobaccojournal.com/news/uk-announces-tobacco-duty-hike/), the same timing-driven boost will not repeat in the December 2026 y/y comparison, creating a mechanical downward base-effect risk on the print versus a naïve trend extrapolation. - [2025-12-19] Air fares—one of December's most volatile CPI drivers—rose sharply in Dec 2025: the largest upward effect came from air fares, which rose by 28.6% in December 2025, whereas air fares rose by only 16.2% the year before, the third-lowest December rise since monthly price collection began in 2001 . A high 2025 base for this volatile, hard-to-forecast component adds two-sided uncertainty to the exact December 2026 y/y figure that BoE/Treasury Q4-average forecasts cannot fully capture. - [2026-09-21] Government has already legislated a disinflationary offset to the energy shock: on 21 July 2026 the government announced a temporary zero rate of VAT for qualifying supplies of electricity in Great Britain, applying from 1 October 2026 to 31 March 2027 , i.e., covering the entire October–December 2026 window relevant to this market, which mechanically depresses electricity CPI relative to a no-policy counterfactual. - [2026-08-26] Ofgem's confirmed Q4 cap already nets out this VAT relief: confirming the October cap on 26 August, Ofgem said that without the VAT cut the cap would have been around £45 higher, and the saving is already included in the confirmed cap figure — meaning some of the "upside" energy narrative used by BoE/Treasury forecasters is partially pre-offset by fiscal policy, reducing the odds of an outsized upside miss but also of it landing squarely mid-band. - [2026-07-26] Independent commentary flags this offset may be immaterial to household experience but is still a real CPI-methodology effect: forecasters expect the Q4 price cap, confirmed on 26 August, to rise by a similar or larger amount, so many households may not notice a change in what they pay — implying the VAT cut mutes but does not reverse the energy-driven inflation path, keeping the outcome finely balanced around the band's edges rather than confidently inside it. - [2026-09-25] Ofgem's next cap decision (Jan–Mar 2027), which shapes the trajectory but not the December print itself, remains unconfirmed and highly uncertain: the Jan–Mar 2027 energy price cap forecast points to a sharp rise, but it isn't confirmed until Ofgem's announcement around 25 November 2026, with MoneySavingExpert currently pointing to roughly a 24.9% rise — this real-time volatility in the cost pipeline underscores that any Q4-average-based point forecast (BoE 3.75%, Treasury panel 3.4%) carries wide, unresolved error bands specifically around December. - [2026-09-09] Upstream energy costs remain elevated and volatile, complicating any single-month pinpoint forecast: the Brent crude oil spot price increased to an average of $91 per barrel in August, $7/b higher than in July, as global crude oil prices rose amid continued Middle East export constraints , while EIA's own baseline still assumes oil prices staying near the August average in the coming months before falling as Middle East supply constraints ease into 2Q27 — a still-fluid geopolitical variable that could push the December fuel-price contribution either higher (renewed disruption) or lower (a faster resolution) than currently pencilled in. - [2026-09-21] Money markets are now pricing further BoE tightening, not just holding, on the back of the inflation overshoot: as of 21 September 2026, money markets were pricing in around a 65% probability of a Bank of England rate rise in November, a significant change from earlier in the year when markets had been considering rate cuts, driven by higher energy prices and renewed inflation concerns . A more hawkish policy path than assumed in the July MPR could itself dampen demand-driven pricing power before December, another way the outturn could undershoot the 3.75% central case implied by BoE's own September update. - [2026-11-05] A fresh, and likely decisive, official forecast update lands well before the December data: the next Bank of England interest rate decision is scheduled for 5 November 2026, followed by the final meeting of the year on 17 December 2026, with the November meeting accompanied by an updated Monetary Policy Report . This means the 3.75%/"slightly above 4%" figures colleagues cite are already two months stale relative to the resolution date, and the BoE's own forecast has moved by roughly half a point in each of the last two quarterly cycles (July→September), illustrating how quickly the specific December print could still shift outside the 3.5–3.9% band in either direction. - [2026-09-17] The BoE's own newest published path explicitly has inflation still rising through the window, not stabilising in it: on 17 September, the MPC said inflation is expected to rise in coming quarters, reaching "slightly above 4% in 2027 Q1" , meaning the Bank's own trajectory has December sitting on the rising leg toward a sub-4%-but-climbing path — a profile consistent with December landing at or just above 3.9%, i.e., outside the band on the upside, rather than settling within it. - [2026-09-21] Historical precedent for large forecast misses in this exact release is recent and specific: in the 12 months to November 2025, CPI rose by 3.2%, below analyst predictions that had been as high as 3.6%, with the Bank of England projecting CPI would fall to 3.0% in January and to 2.5% by Q4 2026 — a forecast that, in hindsight, was wrong by over a full percentage point for Q4 2026 within just ten months, illustrating how unreliable single-point BoE/analyst Q4 calls have been for this very indicator in the very recent past. BOTTOM LINE: The strongest NO case does not rest on inflation "returning to normal" but on the band being too narrow to survive either (a) a base-effect-driven undershoot from the unwinding of 2025's one-off tobacco-duty and airfare timing quirks and the now-legislated electricity VAT cut, or (b) an overshoot past 3.9% given the BoE's own upward-revised path ("slightly above 4% in 2027 Q1") and a volatile, unresolved Middle East energy shock still working through Q4 costs; both the July 30 and September 17 BoE forecast vintages already moved by ~0.5pp against each other, and a fresh November 5 MPR update could move the implied December path again before the print, making a two-sided miss outside 3.5–3.9% at least as plausible as a hit inside it. NOT FOUND: No official BoE or OBR fan-chart probability specifically for the December 2026 (as opposed to Q4-average) CPI print; no confirmed January 2027 Ofgem price cap (due ~25 November 2026), which affects sentiment/pass-through into December pricing but not the December print itself; no post-5-November-2026 MPR data (not yet published as of this research).