How the window and the saving are worked out.

The baseline is your habit

Every saving is measured against the usual start you tell us — not a best case or a national average. If you would normally run the wash at 19:00, that is the number the recommended window is compared to. Change the baseline and the saving changes with it.

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.

Confidence, not certainty

Forecasts move. A High-confidence window sits in a broad, stable trough where a small error will not change the advice. Low means the saving is real but sensitive to how the day turns out. This is decision support — you decide.

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.