Against staying on a capped standard tariff at the Oct–Dec 2026 rates: £273 on Octopus 12M Fixed, plus the £50 referral credit.
Your year on each tariff
2,529 kWh elec · 9,610 kWh gas- Flexible Octopus
The default variable tariff. Octopus prices it at or a little under the cap, so this is your do-nothing line.
£1,740/yrbaseline · £145/mo - Octopus 12M Fixed
Rates locked for 12 months with no exit fees. Illustrative national rates — your quote will differ.
£1,467/yrsaves £273 · £122/mo
What January could do to the do-nothing line
Cornwall Insight forecasts about £1,872 for the January–March 2027 cap, 8.6% above October. For your usage that would be roughly £1,890 a year on a variable tariff, versus £1,467 if you had fixed at today's illustrative rates — a gap of £424 a year while it lasts. Should you fix?
Follows wholesale prices daily, capped at 100p/kWh electricity and 30p/kWh gas. Cheaper when the market falls, dearer when it spikes. No single figure is honest, so it's not in the table.
Half-hourly pricing. Overnight rates of 5–15p, evening peaks far higher. Your saving depends entirely on how much usage you can shift, which no calculator can know.
National-average direct-debit rates; your region differs. Fixed uses illustrative example rates. octopus reprices fixed with the wholesale market and by region — a live quote for your postcode is the real number. Standing charges included throughout. Electricity is compared at 0% VAT, which applies from 1 October 2026; gas at 5%. Not financial advice — get a live quote before deciding.
🧮How the Calculator Works
Every energy bill is the same sum: units used × unit rate + days × standing charge, once for electricity and once for gas. The calculator runs that sum for your usage at the Ofgem cap rates, then again at each Octopus tariff's rate, and shows you the difference. There is no modelling of your behaviour and no hidden weighting — if you put Ofgem's typical household in (2,500 kWh of electricity, 9,500 kWh of gas), you get Ofgem's own headline figures back: £1,663 for July–September and £1,723 from 1 October.
If you start from your monthly bill instead, the tool assumes you're paying cap rates today and that your electricity-to-gas split is typical, and works backwards to an annual usage. That's a fair assumption for most people on a standard variable tariff with any supplier, which is roughly two-thirds of UK households. If your split is unusual — electric heating, no gas, a hot tub — switch to the kWh option and type the figures from your annual statement.
The compare at switch matters more than it looks. Until 30 September the July cap applies; from 1 October the new cap applies and VAT on electricity drops to 0%. Ofgem quotes October's electricity rates at 0% VAT and July's at 5%, so the two are not directly comparable — the calculator keeps each period internally consistent rather than mixing them. Read the VAT cut guide for why the headline saving is smaller than the Treasury's £45.
📚Every Figure and Where It Comes From
| Figure | Value used | Source |
|---|---|---|
| Jul–Sep 2026 cap | Elec 26.11p/kWh + 57.19p/day; gas 7.33p/kWh + 29.04p/day (inc 5% VAT) | Ofgem |
| Oct–Dec 2026 cap | Elec 26.32p/kWh + 54.83p/day (0% VAT); gas 7.97p/kWh + 29.68p/day (inc 5% VAT) | Ofgem, 26 Aug 2026 |
| Typical household | 2,500 kWh electricity, 9,500 kWh gas per year | Ofgem TDCV from 1 July 2026 — see our explainer |
| Jan–Mar 2027 forecast | £1,872 typical, ≈ +8.7% on October | Cornwall Insight |
| Octopus 12M Fixed | Illustrative: elec ~23.3p + ~44.3p/day; gas ~6.7p + ~29.5p/day (July basis, re-stated to the period's VAT) | Our Octopus Fixed review |
| Intelligent Octopus Go | ~7p/kWh for scheduled charging; daytime near Flexible | Our Intelligent Go review |
| Export | Outgoing Octopus 12p/kWh flat vs a typical 4.1p SEG rate | Our export tariffs guide |
| EV efficiency | 3.5 miles per kWh | A mid-range real-world figure; adjust the miles to compensate if your car differs |
Two honest limits. First, region: the cap is set separately for each of the fourteen GB distribution regions and the national average sits in the middle, so a household in North Wales and one in London will each be a little off. Second, Fixed is a moving target — Octopus reprices it as forward wholesale gas moves. The illustrative rate is the best public figure we have; your live quote is the real one, and because there are no exit fees you lose nothing by checking it after you switch.
❄️Why the January Line Is the One to Watch
October's 3.6% rise is confirmed and modest. The forecast for January is neither. Cornwall Insight — who called October to within £14 — expect roughly £1,872 for January–March 2027, a further 8.7%, and it arrives in the quarter when a typical home uses far more gas than any other. A percentage on the cap becomes pounds on your bill in exactly the months you can least absorb them.
That is why the calculator shows your January-level cost next to the Fixed figure. The gap between them is what fixing now is really buying: not a saving against October, which is small, but insurance against January, which isn't. Martin Lewis has said people on the cap should fix; the usual catch is exit fees of £25–£150 per fuel elsewhere, which Octopus doesn't charge. Our fix-or-variable guide works through the decision properly, and the price cap predictions page tracks the forecast as it moves.
🔍What the Calculator Deliberately Leaves Out
Tracker and Agile. Octopus Tracker reprices every day and Agile Octopus every half hour. Both can beat every tariff in the table in a soft market and lose to all of them in a spike. Putting a single annual number on either would be a guess, so we describe them and let you decide whether you want market exposure.
Heat pumps. Cosy Octopus has three daily rate bands and its saving depends on how much heating you can shift into the cheap windows. Our heat pump guide covers the running-cost comparison against a gas boiler.
Batteries. A home battery on Octopus Flux or Intelligent Flux earns by timing exports into the evening peak, which is a scheduling question rather than a rate question. The solar and battery guide explains the options.
Octoplus. Points, Saving Sessions and the prize draw are real money for some households and nothing for others. They're covered in the Octoplus guide and excluded here so the headline figure only contains things you can count on. The one exception is the £50 referral credit, which is fixed, automatic and the same whichever tariff you choose.
Sources: Ofgem — energy price cap · Cornwall Insight — cap forecasts. Figures last checked September 2026.