How the window and the saving are worked out.

The comparison start is yours

Every reportable planning difference is measured against the preferred start you explicitly provide. It is not a best case, a national average, or an inferred usual time. If you do not provide one, the planner can still recommend a feasible window but does not report a cost or carbon difference.

Two channels: price and carbon

Price comes from your tariff — half-hourly Octopus Agile rates, or the Economy 7 / flat rate you enter. Carbon comes from the regional forecast, drawn as the band's bars. We score each possible start on both and let you weight which matters more.

Carbon is regional, not per-postcode

Grid carbon intensity is published by region (a GSP group), so we say "South West England region", never your street. Northern Ireland has no live GB feed, so we use a typical-day EirGrid profile and label it as such.

A robustness indicator, not a probability

The Strong, Mixed, or Fragile indicator combines how decisive the preferred window is with forecast horizon, carbon-data type, and tariff provenance. It is deterministic and uncalibrated: it helps expose sensitivity, but it is not a probability and does not guarantee an outcome.

Open source. Price: Octopus Agile API. Carbon: NESO / National Grid Carbon Intensity regional forecast (GB); EirGrid typical-day profile (Northern Ireland). Appliance energy figures are typical published values — adjust them to your own if you know them.