R3 — Label every published estimate as an estimate, and show its vintage prominently

Rule: Every customer-facing calculator result must be (a) prominently labelled as an estimate, not a quote; (b) accompanied by the date and inputs the figure was based on; (c) accompanied by a one-line statement of what the estimate does not include.

Why: Labelling is the central legal defence (Estimate vs quotation — the legal distinction and why "it's just an estimate" may not save you); courts assess estimate-vs-quote objectively, but unambiguous labelling and visible vintage both work for the defendant. Vintage protects against the staleness failure mode (Solar incentives can change daily — unmaintained solar calculators actively mislead). The Zillow Zestimate case (Zillow Zestimate published error rates — ~1.9% on-market, ~7.5% off-market; lawsuits; 7th Circuit 2019 sided with Zillow partly because "estimate" was clearly labelled) is the worked example: the courts sided with Zillow partly because the figure was always called an estimate, not an appraisal.

How to apply:

• Every result page shows the label "Estimate" near the number, not buried in fine print.
• Every result page shows the input-date and the assumption set.
• One sentence at minimum on what the estimate excludes (taxes, site assessment, scope changes, etc).