Method
How Ember EV estimates a saving.
This page has no pound figure on it. The public stats feed does not yet include the average Agile price on the same dates as the charges, so Ember EV does not print a fleet saving here.
Inside the scheduler, a session's estimated saving is the gap between the window's average unit rate and a flat rate, times the energy added. The flat rate is the previous tariff stored on the account. When that rate is missing, the code uses 15.41p/kWh. That fallback is not a promise and it is not the price-cap rate.
The homepage calculator shows the window and the unit cost. It does not turn that into a saving, because it does not know your old tariff.