Data sources & methodology

Last updated 22 October 2026

Data sources

• Prices and standing charges: the public Octopus Energy REST API (https://api.octopus.energy/v1), documented at developer.octopus.energy. No account or API key is used.
• Product versions: discovered from the Octopus products list. If discovery fails we fall back to AGILE-24-10-01 (import) and AGILE-OUTGOING-19-05-13 (export). The product and tariff code in use are shown on every page.
• Postcode to region: Octopus's grid-supply-point lookup, with postcodes.io used to find a nearby full postcode for partial postcodes.

Prices and VAT

Prices are Octopus’s published “including VAT” figures. AgileWatch never adds VAT itself, so any VAT change (including temporary zero-rating of domestic electricity) is reflected exactly as Octopus applies it. Export rates carry no VAT.

Days, clock changes and publication

All times are UK local time (Europe/London). A normal day has 48 half-hours, the spring clock change 46 and the autumn change 50 — we never assume 48. Agile prices are published once a day, normally between 4:00 and 4:30 PM UK, covering 23:00 that evening to 23:00 the next day. So before 4pm today's 23:00–00:00 prices don't exist yet, and tomorrow's final hour arrives the day after. Any half-hour without a published price is shown as “not published” and never filled with an estimate.

Data checks

Every response is validated: malformed rows are dropped, duplicate half-hours removed, results sorted by time, and prices beyond ±100p/kWh flagged. Any issues are shown on the page under “Data check”. We show when prices were last synced from Octopus, and if Octopus can't be reached we show the last good data clearly labelled as such.

Colour bands and the peak window

Import bands use the price shown to one decimal place: ≤0p plunge, up to 12p very cheap, up to 22p below cap, up to 34.9p elevated, 35p and above expensive. Separately, the 4:00–7:00 PM window, when Agile import adds its peak premium, is shaded on the charts. A high price outside that window is labelled expensive, not peak premium.

Calculators

• Appliance window: finds the unbroken run of half-hours with the lowest total cost for a steady power draw, and compares it with starting at the earliest time you allow. Costs = kWh × p/kWh.
• EV & battery optimiser: energy from the grid = capacity × (target − current) ÷ charging efficiency. “Cheapest slots” picks the lowest-priced half-hours before your deadline; “continuous” finds the cheapest unbroken block. The last half-hour can be partial.
• Agile vs Tracker: applies each day's published Agile half-hourly prices, Tracker daily rate and both standing charges to your usage. Days with incomplete data are left out and listed.

Calculations use full precision; rounding is for display only.

Reference figures

• approx. Ofgem price cap unit rate (~24.5p/kWh): Approximate GB average direct-debit electricity unit rate under the Ofgem cap. Your region and payment method will differ — check ofgem.gov.uk.
• Octopus Outgoing Fixed (reference) (15p/kWh): Reference flat export rate for comparison. Check octopus.energy for the current Outgoing Fixed rate.

Caching

Live prices are cached at the edge for up to 5 minutes (1 minute while tomorrow's prices are due). Completed past days are cached for a week, because published Agile prices don't change.