Build a monthly baseline
Track electricity kWh, gas therms and water gallons separately from dollars. Include billing days and household occupancy so the series remains interpretable.
Annotate the causes
Mark heat waves, freezes, travel, guests, EV charging and irrigation. The goal is not a perfect model; it is a record that makes large changes explainable.
- Usage per day
- Effective variable rate
- Fixed charges
- Weather and occupancy note
Change one thing at a time
After identifying the biggest flexible load, test one operating change and compare the next normalized period. Avoid attributing an entire seasonal swing to a small device.
Worked example: separate quantity from price
Month A uses 600 kWh over 30 days at an effective variable price of $0.15 per kWh. Month B uses 750 kWh over 30 days at $0.17. The usage effect at the old price is 150 × $0.15 = $22.50; applying the two-cent price change to 750 kWh adds another $15.00.
This decomposition does not prove why usage changed. Add heating or cooling degree days, occupancy and known loads to the worksheet, then compare the same normalized fields in the next period.
Treat a seasonal comparison as evidence only when service days, units, variable price, fixed charges, weather and occupancy are recorded separately.
Primary sources and scope
These links support the units or diagnostic method used above. They do not replace your provider’s current tariff, bill or safety instructions.
- EIA — Degree days ↗ — Defines heating and cooling degree days and their use in seasonal comparisons.
- EIA — Retail prices versus utility rates ↗ — Explains the limits of aggregate price data for individual customer rates.
This guide explains general billing math. Utility tariffs and local rules control your actual charges. Sources and update practices are documented in our methodology.
Read the methodology →