Fix North Dakota 2026 income tax thresholds

[PavelMakarchuk]

Summary

• add official TY2026 North Dakota individual income-tax thresholds for every filing status
• pin the complete official schedule in raw parameter assertions
• test the marginal schedule at and immediately above both boundaries for all five statuses

Source

North Dakota Office of State Tax Commissioner, 2026 Form ND-1ES, page 2.

Checks

• make format (includes Ruff formatting and lint)
• uv run pytest -c pyproject.toml policyengine_us/tests/core/test_state_indexed_frozen_parameters.py -k nd -q (32 passed)
• focused ND boundary YAML (37 passed)
• full ND income-tax YAML suite (73 passed)
• uv run pytest -c pyproject.toml policyengine_us/tests/test_parameter_files.py -q (6 passed)
• independent pre-PR review: CLEAN; no actionable findings

[PavelMakarchuk]

@MaxGhenis This is ready for maintainer review: exact head ec61a0344d is now 31/31 green. The sole first-attempt failure was an unrelated Hugging Face CAS download error after five retries in Baseline (rest-b); rerunning that failed job passed. Independent review and all focused ND checks are clean.

[DTrim99]

Program Review — PR #9165 (Fix North Dakota 2026 income tax thresholds)

Author: PavelMakarchuk

Source Documents

• ND Office of State Tax Commissioner, 2026 Form ND-1ES (SFN 28709, 12-2025), page 2 — "2026 Forms ND-1 and ND-EZ Tax Rate Schedules" · PDF #page=2

Branch Status

⚠ 6 commits behind main (1 ahead). Minor; review scoped to the merge-base diff.

Summary

Clean, correct TY2026 value update across all five filing statuses. 0 critical. Every 2026 bracket threshold matches ND-1ES 2026 p.2 exactly, correctly routed to the right status, correctly dated at 2026-01-01 with prior years untouched, the 3-tier scale structure (0% / 1.95% / 2.50%) preserved, and the frozen-parameter test + per-status boundary tests are aligned. CI green (31/31).

PDF / value audit — all 10 thresholds match ND-1ES 2026 p.2

Status	1.95% start	2.50% start	✓
Single	49,575	250,400	✅
MFJ + Qualifying Surviving Spouse	82,800	304,850	✅
Married filing separately	41,400	152,425	✅
Head of household	66,400	277,600	✅

Base-amount cross-checks reproduce the form's printed "your tax is" column exactly ((250,400−49,575)×0.0195 = $3,916.09; MFJ $4,329.98; separate $2,164.99; HoH $4,118.40). MFJ and QSS correctly share one schedule per the form; no status file received another's thresholds; nd_income_tax_before_credits.py routes each status to its own scale. No mismatches.

Critical

None.

Should Address (minor / cosmetic)

1. Reference title wording. The 2026 reference title on each of the five files reads "2026 North Dakota estimated income tax worksheet," but the schedule lives on the Form ND-1ES tax rate schedules page (the frozen-param test docstring correctly calls it that). The #page=2 href is correct and file-page-accurate — only the title wording is slightly off. Consider "2026 North Dakota Form ND-1ES tax rate schedules" for consistency.
2. Pre-existing (not from this PR): joint.yaml carries 0.0250 trailing-zero rate values on the 2023-01-01 top bracket (should be 0.025; the other four files are correct). Since joint.yaml is a touched file, worth a cleanup pass — but not introduced here, and the new 2026 threshold values are all correctly formatted.

Suggestions (optional)

• The 20 new test cases use free-form names rather than the file's existing Test N, … numbered convention (arguably more readable; correctly appended at the bottom).
• The "at/just-above threshold" currency cases assert fractional-cent outputs (e.g. 3_916.0875) with no absolute_error_margin; adding 0.01 would match house style (they pass exactly as-is, so this makes them stricter, not vacuous). A one-line #($1 over × 1.95%) comment would clarify the 0.0195 outputs.

Validation Summary

Check	Result
Regulatory / Value Audit	All 10 thresholds exact-match ND-1ES 2026 p.2; base-amount cross-checks reproduce; MFJ+QSS shared correctly; 0 mismatches
Reference Quality	ND-1ES cited on each of 5 files with correct #page=2; statute subsection preserved; minor title-wording nit
Code Patterns	0 critical; clean 2026-01-01 keys across all 5 statuses, scale structure intact, frozen-param test + changelog aligned; 1 pre-existing trailing-zero
Test Coverage	Tight — all 5 statuses tested at AND just-above both bracket boundaries (20 cases); would catch a transposed threshold or wrong-schedule routing
CI Status	Passing (31/31)

Review Severity: APPROVE

An exemplary, fully-verified 2026 multi-status threshold update: every value matched against ND-1ES 2026 p.2 with base-amount cross-checks, correct MFJ/QSS sharing, and comprehensive per-status boundary tests. No functional issues — only a cosmetic reference-title wording fix and a pre-existing trailing-zero cleanup. Rebase off the 6-commit lag before merge.

Review generated with Claude Code via /review-program

[DTrim99]

Small Claude nits