Methodology

The tariff model

Each rate plan is the current version of a residential tariff in the OpenEI Utility Rate Database (URDB), read without simplification: a fixed monthly charge (converted from a daily charge where the utility bills per day), an optional minimum bill, and energy prices by period, each period with its own tiers. Which period applies is set hour by hour for weekdays and weekends in each of the 12 months, exactly as URDB records it, so seasons follow the utility’s own months rather than a fixed summer. Per-kWh prices include the adjustments and riders URDB lists with the base rate.

Checks before a plan is published

A plan is shown only if its all-in price for a typical home in the state lands within a tolerance of what the utility actually billed residential customers per kWh in EIA-861 (2024), scaled by the state’s price change since then: 72–138% for flat and tiered plans and 60–160% for time-of-use plans, whose average depends more on when you use power. This catches URDB records that hold only the delivery part of a bill, or contain a data-entry error. Where URDB keeps two versions of a schedule, the one closer to the billed price is used. Plans with demand charges are left out, because they need your peak kW, which a calculator cannot know.

A typical home, hour by hour

Monthly use starts from EIA: the state’s residential sales per customer in each calendar month over the last 12 months (where EIA withholds a month, the same month a year earlier). Within each month it is spread over the hours of a weekday and a weekend day with the load shape of the state’s single-family homes from NREL’s ResStock end-use load profiles (2025 release, 2018 weather), converted from Eastern Standard Time to the state’s local clock time with daylight saving. Where you enter your own monthly use, the same shape is scaled to it.

Pricing a bill and an added load

Each month’s bill adds up the kWh in every hour of every weekday and weekend day (calendar days, 5/7 of them weekdays; holidays count as weekdays), prices each period, applies tiers on the month’s total, and adds the fixed charge, with the minimum bill as a floor. When a plan has both tiers and periods, each period’s kWh are split across the tiers in proportion to the month’s total, the convention URDB and NREL’s SAM use. The cost of an EV, an appliance or a heat pump is the difference between the year’s bills with and without it, so the added kWh land in the right tier and the right hours. “Summer” and “winter” views show July and January; every yearly figure sums all 12 months.

EV charging

Energy from the wall equals miles × the EPA combined rating in kWh per 100 miles. EPA measures that figure at the outlet on Level 2 charging, so charging losses are already included and nothing is added on top. Charging runs from the chosen start hour at 7.2 kW (Level 2) or 1.4 kW (Level 1). A “full-range charge” is the wall energy for the car’s EPA range. The gasoline comparison uses EIA’s monthly retail price of regular gasoline for the state, or for its PADD region where EIA does not publish the state. Fast charging is compared only when you enter a price, because no official average exists.

Solar

Production comes hour by hour from NREL’s PVWatts v8 for 1 kW-DC at the state’s 2020 centre of population (south-facing, 20° tilt, 14% losses), averaged into a typical day for each month and converted to clock time. Each hour, the solar that the home uses at once replaces imports; the rest is exported. Under net metering, exports offset use within the same month at the plan’s own prices, credits carry forward, and any left in December are not paid out. Under net billing, imports are billed on the plan and each exported kWh earns the export credit. The export rule comes from URDB; the export credit from URDB when the utility publishes it, otherwise you enter it. Panels lose 0.5% a year, and savings grow with the price increase you choose, which defaults to the state’s average yearly change over the last 10 years.

Heat pumps

Useful heat equals the gas used for heating × furnace AFUE. The default gas use is the state’s average residential gas use per customer (EIA) × the share of home gas that goes to space heating in ResStock. The heat pump supplies the same heat using kWh = heat ÷ its seasonal COP, taken as HSPF2 ÷ 3.412 (1 therm = 29.307 kWh). Those kWh are placed in the months and hours that ResStock’s gas-heated homes need heat and priced on your plan like any added load. The gas price is the state’s 12-month residential average from EIA, which includes the utility’s fixed charges spread over the therms.

Sources and default values

What is not included

• Sales taxes, franchise fees and riders that URDB does not record.
• Low-income discounts, medical baseline allowances and demand charges.
• Baseline regions other than the one named on the plan: in California, for example, tier limits depend on your climate zone.
• Holiday calendars, and events such as critical-peak days.
• Your own interval data. For the most accurate comparison, download your Green Button data from your utility and compare it with the typical-home shape used here.