What this page does. Tell it how much power your load draws and how long it needs to run, and it finds the cheapest continuous window among the Agile Octopus prices published for today and tomorrow, with the estimated cost compared with starting straight away.
How this page is made. The numbers below are fetched automatically from the public sources listed at the bottom and are not edited by us. The text on this page is prepared with AI assistance and checked against those sources. Drafts are prepared with AI assistance and checked against the sources listed on this page. They are not reviewed by a qualified electrician. Page text last checked: 4 November 2026. Spotted a mistake? Email editorial@uksmartplugs.co.uk. See How we work.
Examples (numbers to edit, not recommendations): 7 kW for 4 hours · 2 kW for 1.5 hours · 1 kW for 3 hours
Result for 1 kW for 3 hours (3 kWh) in London
| Option | Time (UK) | Average price incl. VAT | Estimated cost |
|---|---|---|---|
| Cheapest window | Wed 11:30 to Wed 14:30 | 34.1p/kWh | £1.02 |
| Starting as soon as possible | Wed 11:30 to Wed 14:30 | 34.1p/kWh | £1.02 |
| Most expensive window | Wed 16:00 to Wed 19:00 | 56.9p/kWh | £1.71 |
Starting as soon as possible is already the cheapest option among the prices published so far.
Estimate: assumes the load draws a constant 1 kW for the whole run; unit rate only, no standing charge. Data last fetched 4 November 2026, 11:39 UK time.
How it works
- Agile prices change every half hour. The tool tries every possible start time and adds up the price of each half-hour of your run.
- The cost is power in kW × hours × price. A 2 kW load for 1.5 hours uses 3 kWh.
- It only looks at prices that are already published, so before about 4pm it can only see until the end of today.
Finding your load’s power
The rating plate on an appliance or charger gives its power in watts (W) or kilowatts (kW); divide watts by 1,000 to get kW. Many appliances draw less than the plate figure for much of a cycle, so treat the result as an estimate. Our running-cost calculator explains the maths, and today’s prices show the full day.
Safety first
A cheap window is not a reason to leave something running unattended. Only use delay-start or timers on appliances whose manufacturer allows it, and read what not to plug into a smart plug. If you charge an electric vehicle, use a proper EV charge point or the charger’s own timer or app; our guide explains why a 3-pin granny charger should not be run through a smart plug.
Where the data comes from
- Agile Octopus unit rates: Octopus Energy’s public API (developer.octopus.energy). Pence per kWh including VAT, for the region you pick.
Limits
- These are unit rates only; they do not include your standing charge.
- We are independent. We are not affiliated with Octopus Energy and we earn nothing from this page.
- This page is information, not financial advice. If the source cannot be reached we show the last figures we have, with a warning.
- The tool assumes a constant power for the whole run. Real appliances vary, and some EV chargers taper off near a full battery.