Window Replacement ROI Calculator accuracy and testing

Formula source

• Payback = (project cost - incentives - home value increase) / annual savings. ROI = total benefit over years / net project cost.

Test cases

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

• All prices, rates, taxes, and usage values are entered by the user.
• Calculations run locally in your browser and are not stored by Calwarden.
• This is planning math, not financial, tax, engineering, or legal advice.

Unit handling

• Project Cost accepts values in $.
• Incentives/Rebates accepts values in $.
• Annual Energy Savings accepts values in $/yr.
• Maintenance Savings accepts values in $/yr.
• Estimated Home Value Impact accepts values in $.
• Analysis Period accepts values in years.
• Estimated Payback is displayed in years.
• Net Project Cost is displayed as currency.
• ROI Over Analysis Period is displayed as a percentage.
• Net Benefit 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.
• Percent outputs are displayed with two decimal places.
• Input precision follows configured step values where provided.

Version history

Change log