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Watt Happens Next · Chapter 10

Audit the Bill

Most bills are right, and now you can prove it. Rebuild every line from the units, the rate and the days; where a line is built on an estimated read, your own read shows what it should be.

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

The bill's period

Electricity: what the bill says, and your own read

Gas: what the bill says, and your own read

Enter the bill's lines and your own reads, then press Calculate.

The formula

  • Each energy line = kWh billed × the unit rate; each standing line = days × the standing charge
  • A line matches when your sum and the printed amount agree to the cent (a rounding of 0.01 is fine)
  • An E (estimated) read is the supplier's guess: the difference = (kWh billed − kWh from your reads) × the unit rate
  • The bill on your reads = the bill as sent − the differences
The book's worked example, Chapter 10. The book's bill, 31 days: electricity 301.4 kWh × 0.26 = 78.36 and 17.05 standing; gas 2,980 kWh × 0.08 = 238.40 and 9.30 standing: 343.11, and every line adds up. But the gas read is marked E: our own read says 2,698 kWh, so the estimate is 282 kWh (22.56) too high. On our read the bill is 320.55.
Check it. Photograph the meter on the bill's closing date. If the bill says E, send that read and ask for a corrected bill.

Honest limits. Bills can carry lines this sheet does not (tax, credits, adjustments): add them by hand. Keep paying the part that is not in dispute. UK: the supplier first, then the Energy Ombudsman after 8 weeks or a deadlock letter; Ofgem's 12-month back-billing rule. US: the utility in writing, then the state public utility commission. Rules change: check the regulator's page. 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.