Methodology

The math is deterministic finance math

Every RetrofitROI tool runs closed-form finance calculations in your browser: simple payback period, financing-comparison math across cash, loan, lease, and PPA structures, and explicit breakeven solving for the variable that would need to change for a different option to win. There is no black-box estimate, no live model call, and no server-side computation. The formula behind a result is the same formula every time you run it with the same inputs.

Where each number in a result comes from

A value feeding into a result is always one of four kinds, and a result states which kind applies where it matters:

• What you typed into that specific tool, for that specific question.
• A value carried from another tool, such as your electricity rate or your home's climate zone, reused so you do not retype it. A reused value is always marked "from a previous calculator" and stays editable.
• A calculated output, produced from the inputs above by the tool's own formula.
• A planning default, shown when a figure genuinely varies by household and you have not entered your own number yet. A planning default is always labeled as an estimate, sourced on the sources page, and replaceable with your own figure at any time.

A federal, state, or utility incentive is never defaulted to a nonzero number. If a tool needs an incentive amount, it asks you to enter a confirmed figure, because incentive rules change by program and by household and a guessed number would be worse than none.

What a result actually shows

A substantive result does not stop at one number. It shows the answer, what that number means for your situation, the cost components that make it up, the tradeoff each option carries, at least one conclusion you did not explicitly ask for but that changes the decision, and a breakeven or payback point when one exists and is mathematically meaningful. Where a small number of variables would materially change the conclusion, the result lets you adjust them and see the answer update live, rather than making you rerun the tool from scratch.

When no practical breakeven exists within a reasonable range, a result says so plainly instead of forcing a number that would be misleading.

What RetrofitROI does not attempt to calculate

RetrofitROI does not perform sizing, ampacity, load-calculation, or code-compliance math of any kind: no wire gauge, no breaker size, no BTU load requirement. That is a categorically different question, aimed at the person doing an installation rather than the person deciding whether to buy, and it belongs with a licensed contractor or a dedicated trade tool, not here. See the disclaimer page for the complete list of what is out of scope.