How the Bill Change Comparison Works
Bill change = modeled billing-period effect + modeled daily-usage effect + remaining rate-and-charge effect
The calculator converts each complete bill into kWh per day, bill amount per day, and effective all-in cost per kWh. It holds previous daily use and effective cost constant for the billing-period effect, holds previous effective cost constant for the daily-usage effect, and assigns the remaining amount to a combined rate-and-charge effect.
The remaining effect is not a pure rate increase. It may include tariff structure, fixed charges, taxes, credits, or other bill components. The comparison shows association, not equipment diagnosis or proof of causation.
Frequently Asked Questions
Does the remaining effect mean my utility raised its rate?
Not necessarily. It may include a changed effective energy price, fixed charges, taxes, credits, tariff tiers, or other bill components. Check the line items and tariff on both bills.
Why compare kWh per day?
Billing periods can have different lengths. kWh per day separates period length from average daily electricity use.
Can this calculator diagnose an appliance problem?
No. It compares bill data and models associations. Use the Home Audit to rank entered appliance estimates, and measure or check equipment labels when practical and safe.