The EPEX spot market: what it is and why it matters
Electricity in the UK is bought and sold on wholesale markets before it ever reaches your home. The most important of these for Agile pricing is EPEX Spot, the European Power Exchange. It operates a day-ahead auction that runs every afternoon across European markets, including the UK.
In the day-ahead auction, electricity generators, large industrial consumers, and energy traders submit buy and sell orders for every half-hourly period of the following day. The market clears at the price where supply and demand balance for each slot. That clearing price becomes the wholesale rate that underpins Octopus Agile prices.
This is not an abstraction. The price set in the EPEX auction directly reflects the expected cost of generating electricity at each moment tomorrow. A slot at 3am on a windy forecast day might clear at 2-4p/kWh equivalent. A slot at 6pm on a cold, calm day when gas peakers are expected to run might clear at 15-25p/kWh equivalent. The market incorporates every piece of publicly available information about tomorrow's supply and demand into a single number per half-hour.
Octopus takes those wholesale prices, adds the regional distribution network charges for your DNO area, applies VAT, and produces your Agile unit rates. The result is a set of 48 prices per region that reflect the true economics of electricity generation and delivery, without the artificial smoothing of a flat-rate tariff.
How tomorrow's 48 half-hourly prices are calculated
The EPEX day-ahead auction closes around midday. Market clearing and settlement takes a few hours. By early afternoon, the wholesale prices for every half-hour of the following day are confirmed and begin flowing through to suppliers.
Octopus applies the following steps to convert wholesale prices into your Agile rates:
Step 1: Wholesale base price. The EPEX day-ahead clearing price for each half-hour in pounds per megawatt hour is converted to pence per kilowatt hour. A wholesale price of £50/MWh becomes 5p/kWh.
Step 2: Regional distribution charges. Your DNO's network use of system charges are added. These vary by region and reflect the cost of delivering electricity through local infrastructure. They add between 5-9p/kWh depending on your area.
Step 3: Supplier margin and levies. Other system costs including transmission charges, balancing costs, and government levies are added. Octopus also applies a small retail margin.
Step 4: VAT. 5% VAT is applied to the final rate.
Step 5: Cap check. Octopus applies an internal cap of 100p/kWh to prevent extreme prices reaching customers during market stress events.
The resulting 48 prices per region are published to the Octopus API, reflected in the Octopus app, and displayed on the AgileAlert dashboard, all by around 4pm each afternoon.
When prices are published and how to access them
New Agile prices for the following day go live at approximately 4pm daily. This covers midnight to midnight of the next calendar day, giving you all 48 slots for tomorrow in one go.
There are three ways to access them:
The Octopus Energy app. If you're an Octopus customer, your app shows a price chart for the current and next day. It's clear and colour-coded, but it doesn't offer region comparison or push notifications for plunge events.
The Octopus API. Octopus publishes its prices as a public API. Technically minded customers can query it directly, and many home automation systems including Home Assistant use it to automate appliances based on live prices.
AgileAlert. The AgileAlert dashboard shows half-hourly prices for all 14 UK regions on a single screen, updated continuously. You can see where tonight's cheap windows are, compare regions, and identify plunge events without needing a technical setup. It's free and requires no account.
The 4pm publication time matters because it gives you the whole evening to plan. Check the dashboard at 4:30pm, identify the overnight cheap windows for your region, and set your appliance timers before dinner. By the time you're asleep, your washing machine, dishwasher, and EV charger are already running on electricity that costs a fraction of the daytime rate.
What makes prices spike: cold snaps, calm days, high demand
High Agile prices have predictable causes. Understanding them lets you anticipate bad days and avoid them.
Cold weather. When temperatures drop, heating demand surges. Every gas boiler and heat pump running simultaneously creates a demand peak that the grid struggles to meet cheaply. Gas peaker plants run at high cost. Wholesale prices rise sharply, particularly for the 5-8pm evening slots.
Low wind output. Renewables provided 50.8% of UK electricity in 2024. When the wind drops for several days across the UK, that generation disappears and gas and coal step in at much higher cost. A calm winter week can produce Agile peak prices well above 40p/kWh.
High national demand days. Certain dates produce reliably high demand: return-from-Christmas in early January, particularly cold Mondays after mild weekends, and the first cold spell of autumn. These aren't unpredictable, and you can often see them coming a day ahead in the forecast prices.
On spike days, the strategy is straightforward: hold your major loads until overnight, avoid the 5-8pm peak entirely, and wait for prices to fall. The overnight window almost always returns to reasonable levels even after a high-price day.
What makes prices plunge: high wind, low demand, grid surplus
Negative and near-zero prices are the most exciting part of Agile, and they have equally clear causes.
High wind output. UK wind capacity has grown enormously. Wind provided 30% of UK electricity in 2025. On a stormy day, offshore farms can generate at full capacity for hours, flooding the grid with cheap power that exceeds demand. The wholesale price falls. Sometimes it turns negative.
Sunday mornings in spring. Weekend mornings combine low industrial demand with typically high solar output. The grid has power to spare. Prices regularly drop below 5p/kWh on Sunday mornings in spring and autumn. Check the dashboard the night before and set everything to run.
Balancing mechanism overshoot. Grid operators sometimes procure too much reserve generation. When those reserves are dispatched but not needed, the resulting surplus pushes prices sharply negative. These events are short but dramatic, sometimes reaching -20p/kWh for one or two half-hour slots.
Plunge events are visible on AgileAlert as soon as they appear in the published prices. On days when tomorrow's forecast shows high wind, it's worth checking the overnight slots carefully, sometimes the negative prices are already baked into the day-ahead auction before the event happens.
Using AgileAlert to plan ahead
The customers who save the most on Agile share one habit: they check prices in the early evening and set their timers accordingly. Not every day requires a dramatic strategy shift. Most days, it's simply a matter of noting where the overnight cheap window sits and making sure the big appliances run there.
But on the days when something notable is happening, a plunge event forecast overnight, an unusually high price spike for the 6pm slot, or a particularly wide gap between the cheapest and most expensive half-hours, those are the days where a two-minute check on the dashboard translates into meaningful money.
AgileAlert shows the full 48-slot price chart for your region, highlights the cheapest and most expensive windows, and flags negative prices. It's free, requires no account, and updates continuously as new prices land. Check tonight's chart for your region here.
For a deeper understanding of how to read that chart and act on it, see the guide to when Agile prices are published and how to use them.