TechnologyGenerated accuracy model review: 2026-05-06

Device Power Cost accuracy and testing

This page documents how Calwarden builds trust for this calculator: source notes, regression-style default tests, limitations, assumptions, unit handling, rounding, and visible change history.

Formula source

1. **Daily kWh** = (Watts × Hours) / 1000. 2. **Daily Cost** = Daily kWh × Rate. 3. **Monthly Cost** = Daily Cost × 30.

Test cases

Default input regression check

Generated from the checked-in default inputs and calculate function.

Inputs

Electricity Rate Preset: eia_us_residential_average
Device Wattage: 250 W
Hours Used / Day: 8 hrs
Cost per kWh: $0.15

Expected outputs

Monthly Cost: $9.89
Yearly Cost: $120.30
Monthly kWh: 60

Known limitations

This page documents the checked-in calculator logic and does not certify results for every real-world edge case.
Use the result as a planning estimate unless the calculator page states a stricter purpose.

Assumptions

Wattage is treated as a steady average draw over the entered daily runtime.
Monthly cost is estimated using a 30-day month and yearly cost uses 365 days.
Negative wattage, hours, or utility-rate values are invalid.

Unit handling

Electricity Rate Preset accepts one of the configured options.
Device Wattage accepts values in W.
Hours Used / Day accepts values in hrs.
Cost per kWh accepts values in $.
Monthly Cost is displayed as currency.
Yearly Cost is displayed as currency.

Rounding rules

Number displays use up to 2 decimal places in the calculator UI.
Currency outputs are displayed with standard US dollar formatting.

Version history

1.0.0 - 2026-05-06

Generated accuracy and testing page from the current electricity-cost-calculator calculator definition.

Change log

2026-05-06

Published default regression test documentation and metadata fallbacks for Device Power Cost.

Calculator transparency

Accuracy pages are generated from checked-in calculator definitions and can be upgraded with curated review metadata over time.

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