How we calculate your electric bill estimate

The calculator compares two bill totals from your statements. Change in amount = current bill − previous bill. Percent change = that difference ÷ previous bill × 100 when the previous bill is above zero. When the previous bill is zero, percent change is undefined.

With kWh on both bills (and no days entered): effective bill cost per kWh = bill ÷ kWh. Usage effect = (current kWh − previous kWh) × previous unit cost. The rest of the amount change is treated as price, fees, and other bill lines.

With billing days and kWh on both bills, three parts add up exactly to the amount change: period length = (days_now − days_prev) × (bill_prev ÷ days_prev); daily usage = (kWh/day_now − kWh/day_prev) × days_now × (bill_prev ÷ kWh_prev); bill cost / kWh = (unit_now − unit_prev) × kWh_now. That third part includes energy price, fixed fees, taxes, and other lines — the calculator does not say which of those moved.

Example: previous $120 / 30 days / 650 kWh and current $155 / 31 days / 780 kWh → the bill is up $35 (+$4 billing days · +$20 daily use · +$11 bill cost / kWh). With $4,500 monthly income, the latest electric bill is about 3.4% of income.

Without kWh, you only see the amount and percent change. “Estimated bill if usage drops” is a rough estimate assuming the entire bill scales with usage; with kWh it uses bill ÷ kWh. Fixed fees are not separated, so real savings may be lower.

The calculator does not look up a rate by ZIP code. It does not assign the leftover change to one industry or policy cause. “Estimated bill if usage drops” is a rough estimate — fixed fees are not separated, so real savings may be lower. Income is used only for electricity bill as a share of income and is left out of the anonymous share text. Header currency reformats display only.