Sizu Riatto
Watt Happens Next · Chapter 10

Call the Next Bill

Call the bill before it arrives. Your own meter model and the month's normal weather give the number, and an honest band says how far the weather and your habits can move it.

Home › Calculators › Call the Next Bill

Opens on the book's house. Change any number to your own and press Calculate.

The period

Your model

Your tariff

The band

Enter the days, the degree-days and your model, then press Calculate.

The formula

  • Electricity = kWh a day × days; gas = no-heating gas × days + gas per degree-day × degree-days
  • The bill = each fuel's kWh × its unit rate + days × its standing charge
  • The band = ± (the weather share × the heating gas's money + the electricity share × the electricity's money)
  • Sensitivity: change one input by 10% and see how far the bill moves
The book's worked example, Chapter 10. Next bill, 31 days and 290 normal degree-days: electricity 31 × 9.6 = 297.6 kWh; gas 226.2 + 2,339.1 = 2,565.3 kWh. The call: 308.95 ± 22.58 (286.37 to 331.53, ± 7.3%): 18.71 for the weather and 3.87 for the electricity.
Check it. Write your call down before the bill arrives, then score it with the Bill Score calculator.

Honest limits. A call, not a promise: a cold snap, a guest, a new appliance or a tariff change moves the bill. The band is the book's assumption (10% on the weather, 5% on electricity); widen it if your month is unusual. The book's house, its meters and its bill were worked out on paper from published figures, not measured by us: read your own meters and log your own night. Tariffs are illustrative, as seen in November 2026 (shaped like the GB price cap of October to December 2026, with US prices beside), shown without a currency sign; put in your own. No saving is promised. Everything stays in your browser: no sign-up, nothing stored.

These calculators go with Watt Happens Next (Make It Add Up, Book 3), where every number on this page is worked by hand.