Against staying on a capped standard tariff at the Oct–Dec 2026 rates: 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; £50 per fuel to leave early. Costs more than the cap today, but locks in below the January forecast. National-average rates — your quote will differ.
£1,967/yr£227 more today · £164/mo
What January could do to the do-nothing line
Forecasts as of 28 October 2026 put the January–March 2027 cap at about £2,180, roughly 27% above October (plausibly anywhere from 16% to 27%, depending on the Middle East). For your usage that would be roughly £2,202 a year on a variable tariff, versus £1,967 if you had fixed at today's rates — a gap of £235 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 national-average rates for the octopus 12m fixed on sale from 27 october 2026. 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 since 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 applied; since 1 October the new cap applies and VAT on electricity is 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 | ≈ £2,180 typical, ≈ +27% on October (range +16% to +27%) | British Gas (15 Oct) and E.ON Next (26 Oct 2026); Cornwall Insight (30 Sep) for the low end |
| Octopus 12M Fixed | National average, 27 October 2026 version: elec 30.15p/kWh + 53.76p/day at 0% VAT; gas 9.40p/kWh + 28.72p/day inc 5% VAT. £50 per fuel exit fee | Octopus product data, checked 28 Oct 2026 — see 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 national average is the best public figure we have; your live quote is the real one. Flexible Octopus has no exit fees, so you lose nothing by switching first and checking the Fixed quote afterwards.
❄️Why the January Line Is the One to Watch
October's 3.6% rise is confirmed and modest. The forecast for January is neither. Forecasts now put January–March 2027 at around £2,180–£2,185, roughly 27% above October, after E.ON Next raised its forecast to £2,183 on 26 October, level with British Gas (our news report). 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. Against October, today's Octopus fix actually costs a little more; against January's forecast it costs a lot less. Martin Lewis's advice is to compare the whole market for the cheapest fix. The catch with any fix is the exit fee: Octopus charges £50 per fuel to leave its 12-month fix early, against £25–£150 per fuel elsewhere. 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.
Gas user? Try the gas standing charge calculator to see what the Budget's change would mean for you, or compare Octopus prices by region.
Sources: Ofgem — energy price cap · MoneySavingExpert — January forecast round-up · Octopus Energy product data (12M Fixed). Figures last checked September 2026.