/methodology

How we research

The decoder logic, the four credit-pillar pages, and the 50-state conformity grid are derived directly from primary IRS / Treasury / USC / state DOR sources. We re-verify quarterly. When primary sources change, we date-stamp the change and update the affected pins.

last verified2026-05-07·source:law.cornell.edulast verified2026-05-07·source:law.cornell.edulast verified2026-05-07·source:law.cornell.edulast verified2026-05-07·source:law.cornell.edulast verified2026-05-07·source:law.cornell.edu

Process

1 · Primary-source-first

Every credit-percentage, every dollar cap, every IRS Form line, and every USC subsection traces to a primary source. Preference order: irs.gov > home.treasury.gov > federalregister.gov > law.cornell.edu (USC) > ecfr.gov (CFR) > state DOR > court filings > CRS reports. Firm-blog / news sources never primary.

2 · Verbatim quoting

Statutory text (e.g. §25D(e)(8)(A) installation-completion rule, §30D(h) termination clause, §25E(a) credit-amount formula) is quoted verbatim from law.cornell.edu, with the subsection cite. We do not paraphrase the literal statutory language.

3 · CPA / EA reviewer pass

CPA / EA reviewer credentialing is currently pending, so this editorial review has not yet begun — /about and every page footer say so explicitly rather than imply a review that has not happened. Once a credentialed CPA or EA is named, each pillar page and each decoder verdict surface will be reviewed prior to publication and on every quarterly re-verification cycle, and the reviewer's credentials (real CPA license # + state, OR EA enrollment # + state) will appear on /about and on every page footer. We do not invent reviewers.

4 · Date-stamped pins

Every claim carries a last-verified date via the PolicyStatePin component. When a primary source revises (IRS issues a new FAQ, a state DOR posts a conformity ruling, etc.), the affected pins update and the page footer reflects the change.

5 · Quarterly re-verification cron

A staleness cron warns when any policy-state pin or state-conformity row exceeds 90 days without re-verification. Annual full sweep at the start of each filing season (typically January).

6 · No-fabrication rule

If primary text could not be retrieved at the time of writing, the affected claim is marked as verification-pending — never paraphrased and never invented. This applies to credit %, dollar caps, IRS Notice numbers, IRS Letter numbers, state-credit amounts, and reviewer credentials alike.

7 · Privacy

Decoder inputs (install date, contract date, payment date, dollar amount, state) are processed in the user's browser only. Inputs are NEVER POSTed to our servers. We log only aggregate verdict-kind counts (e.g., 'verdict=amend-yes was returned N times this week') for content prioritization. See /privacy.

Statute-citation pipeline preference order

When two sources disagree, the higher-rank source wins. We never cite a firm blog or aggregator as primary for a credit %, dollar cap, USC subsection, IRS Form line, IRS Notice number, or IRS Letter number.

Rank	Source	Used for
1	irs.gov	FAQs, Forms, Form instructions, Newsroom, Pub series
2	home.treasury.gov	Treasury policy guidance and press
3	federalregister.gov	Final / proposed regulations and Notices
4	law.cornell.edu/uscode/text/26	USC primary text via Office of Law Revision Counsel
5	ecfr.gov	Code of Federal Regulations (Treasury / IRS regs)
6	state DOR / state agency	State conformity rulings, state-credit program pages
7	court filings + CRS	Tax Court / appellate decisions; Congressional Research Service reports
—	Firm blogs / news (Plante Moran, NerdWallet, Kiplinger, Grant Thornton, Baker Tilly)	Supplementary characterization only — never primary

Decoder logic — 4 sequential tests

The amend-window decoder applies four primary-source-pinned tests in sequence. Each verdict surface ties back to the controlling statute and (for §30D / §25E) the operative IRS FAQ.

1. §25C(i) placed-in-service test
Scope · §25C — heat pumps, insulation, windows, doors, energy audits
Property must be placed in service before 2026-01-01. NO binding-contract relief.
2. §25D(e)(8)(A) installation-completion test
Scope · §25D — solar, geothermal, battery storage, fuel cell, small wind
Original installation must be completed before 2026-01-01. NO binding-contract relief. Contract + deposit + equipment-on-site is INSUFFICIENT.
3. §30D / §25E binding-contract acquisition test
Scope · §30D + §25E — new and used clean vehicles
Written binding contract + payment (including nominal deposit or trade-in) by 2025-09-30 = vehicle acquired in time, even if delivery is later. Per IRS FAQ FS-2025-05.
4. §6511(a) amend-window check
Scope · All four credits
Generally 3 years from the date the original return was filed. 2025 returns timely-filed by 2026-04-15 stay open through ~2029-04-15.

Note: the "substantial-payment-by-deadline" phrase is a tax-practitioner shorthand — there is no separate primary-source rule with that label. The decoder uses only the three statutory / FAQ tests above for credit eligibility, plus §6511(a) for the amend window. Per Wave 1A digest §10 honest-gap #6.

State-conformity sourcing

Every state-conformity row links to a state DOR or state-agency primary source — never to a third-party scraper or aggregator. Federal-conformity columns default to conforms for income-tax states with rolling IRC conformity unless we have identified a specific decoupling action; the nine no-income-tax states (AK, FL, NV, NH, SD, TN, TX, WA, WY) are flagged not_applicable.

Pragmatic scope (per IDEA-BRIEF deferred decision): the highest-population states are populated with verified primary-source data first. The remaining states + DC carry a verification_status: placeholder flag and a “pending verification — see your state DOR” note. Verified count this sweep (computed live from state-conformity.json): 27 verified / 24 placeholder (out of 51 rows).

Verification roadmap for placeholder rows

Pull state DOR personal-income-tax instructions and check for explicit IRC-conformity language (rolling vs. static; specific decoupling provisions for §25C / §25D / §30D / §25E).
Search state-agency program pages (state energy office, state EV office, state housing finance authority) for independent state-credit programs.
Confirm with state-bar or state-CPA society guidance if state DOR is silent.
Promote row to verification_status: verified with primary-source URL + last-verified date.
Annual full re-sweep at start of each filing season; quarterly staleness check on every row.

Honest gap disclosure

FAQ FS-2025-05 verbatim Q-numbers were resolved by Wave 7 V1 (2026-05-07): Q1–Q7 enumerated, with Q2 = vehicle-acquired definition, Q3 = acquisition effect on credit, Q4 = credit-transfer election timing, Q5 = ECO portal, Q6 = §25C manufacturer reports, Q7 = §25D installation-completion. Re-verified each quarterly cycle against the live FAQ page.
IRS Form 5695 (i5695, Catalog 66412G dated 2026-01-22) and Form 8936 (i8936, Catalog 67912V dated 2025-10-14) line numbers were verified from the actual IRS PDFs in Wave 7 V1 (2026-05-07). Re-pull cron each quarter to catch revision-date bumps.
§25D(g) verbatim “Applicable percentage” schedule is summarized from Cornell; the build re-pulls verbatim text each quarter.
No standalone IRS Notice (n-25-XX) issued for §25C / §25D / §30D / §25E transitional rules. Operative IRS guidance is FS-2025-05 only. Quarterly re-check of irs.gov/pub/irs-drop/ for any subsequent guidance.
The remaining placeholder state rows (24as of the last sweep) are an honest gap; we publish them as “pending verification” rather than guess. See roadmap above.

Last verified · 2026-05-07 · full citation manifest