[MaxGhenis]

Record the Colorado AMT deduction addback source conflict and retain the section 63 deduction base. We preserve the statutory reading while documenting the Department's broader instruction to exclude duplicates.

Colorado applies the section 39-22-104 modifications under C.R.S. 39-22-105(2)(a). Filers compute the deduction addback from deductions claimed under section 63, pursuant to (3)(p.5) and (3)(p.7). The General Assembly does not expressly require substituting deductions allowed for federal AMT.

The Department of Revenue tells filers to exclude duplicate federal adjustments in its 2025 DR 0104AMT instructions, page 1. The Department coordinates other Colorado addbacks under Rule 39-22-104(3)(p.5), paragraphs (1) and (3), without addressing this federal AMT overlap.

Add candidate us-co:dr0104amt-line-2-duplication-bar, capture the deciding instruction excerpt, and test the retained reading for itemizers and standard deduction filers. This follows up on #10099, which merged before this branch started from main.

Hand computations

For a single itemizer earning $450,000, itemized deductions total $30,000: $5,000 state income tax, $5,000 property tax and $20,000 mortgage interest. Federal AMTI equals $430,000. The IRS publishes the 2025 exemption and 2026 exemption and standard deduction.

Year	Federal AMTI less exemption	Colorado deduction addback	Retained Colorado AMTI	AMTI after removing property tax overlap	Normal tax	Retained tentative minimum tax
2025	341,900	30,000 - 12,000 - 5,000 = 13,000	354,900	349,900	438,000 × 4.4% = 19,272	354,900 × 3.47% = 12,315.03
2026	339,900	30,000 - 1,000 - 5,000 = 24,000	363,900	358,900	449,000 × 4.4% = 19,756	363,900 × 3.47% = 12,627.33

Both readings leave these households with zero Colorado AMT. A single standard deduction filer with the same wages retains an addback of $3,750 in 2025 and $15,100 in 2026, giving Colorado AMTI of $365,650 and $375,000.

Invariants

Every household's result equals main because we retain every formula, parameter value and input. We test both itemizer expectations, zero Colorado AMT and standard deduction cases in co_alternative_minimum_taxable_income.yaml. We validate the candidate and marker workflow with test_source_conflicts.py.

Validation

• Colorado AMTI YAML: 10 passed, including the two original itemizers, two new standard deduction cases, and zero-AMT checks.
• Source-conflict guard: 103 passed.
• make format: passed Ruff formatting and checks.
• Independent legal, arithmetic and diff review: approved after wording and citation updates.
• Formula and parameter files equal main.

Methodology choices

• Retain the section 63 deduction base under CONTRIBUTING's statute-first principle. The Department directs filers to exclude duplicates; we record both readings.
• Apply the recorded choice to 2025 and 2026. We verified the 2025 instructions, without claiming verification of a 2026 AMT form.
• Include standard deduction overlap: filers cannot claim that deduction for federal AMT under 26 U.S.C. 56(b)(1)(D).
• Add a candidate without a source-conflict marker. Contributors must first register and pin the implementation under CONTRIBUTING's source-conflict workflow.
• Keep the formulas and parameter values unchanged. We add no rule or threshold to check with Hypothesis or mutant tests.

Microsimulation impact

To be measured before merge.

axiom: n/a: We document an existing reading and add tests without changing an encoded provision. After merge, contributors can register and pin the candidate's implementation and cases.

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