Derive Arkansas 2026+ minus adjustments from the indexed statutory tables

changelog.d/fix-ar-reduction-uprating.fixed.md

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+Make Arkansas income tax projections for 2027 and later consistent. The model now derives the minus adjustments from Act 1 of 2026's indexed statutory tables: table (A), the high-income table (B), and the (C) bracket-adjustment rows. Before, the minus adjustments stayed at their 2026 values while the rate thresholds rose, so tax fell by as much as $111.98 as income crossed a 2026 bound. Rate-table bracket bounds now round to the nearest $100 instead of down, per A.C.A. § 26-51-201(d)(1); this also moves the bounds that projected Arkansas withholding reads. The $94,700 high-income threshold, the (B) 2% row top and each (C) row bound, which were not indexed before, are now indexed and rounded the same way. The (C) dollar amounts stay fixed.

policyengine_us/parameters/gov/states/ar/tax/income/rates/main/high_income/bracket_adjustment.yaml

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+description: Arkansas subtracts this bracket adjustment amount from the high-income tax table result, based on net taxable income.
+metadata:
+  type: single_amount
+  threshold_unit: currency-USD
+  amount_unit: currency-USD
+  label: Arkansas high-income bracket adjustment
+  reference:
+  - title: A.C.A. § 26-51-201(a)(4)(C), as amended by Act 1 of 2026 (1st Extraordinary Session), § 1
+    href: https://www.arkleg.state.ar.us/Home/FTPDocument?path=%2FACTS%2F2026S1%2FPublic%2FACT1.pdf#page=2
+  - title: A.C.A. § 26-51-201(d)(1), as amended by Act 532 of 2023, § 2 (bracket amounts indexed annually, rounded to the nearest $100)
+    href: https://www.arkleg.state.ar.us/Home/FTPDocument?path=%2FACTS%2F2023R%2FPublic%2FACT532.pdf#page=4
+# Each threshold is the "Less Than or Equal To" bound of the row before, and
+# the amount applies to net income ABOVE it (the formula calls calc with
+# right=True): the statute's first row, $94,701-$94,800, is threshold 94,700.
+# Keying rows on these round bounds lets each one be indexed and rounded to the
+# nearest $100 like the high-income threshold, which the first row shares.
+# The dollar amounts are not indexed: 26-51-201(d)(1) indexes only bracket
+# bounds, and DFA's 2022-2025 cards kept each Act's $10 steps.
+brackets:
+  - threshold:
+      values:
+        2026-01-01: 94_700
+      metadata:
+        uprating:
+          parameter: gov.irs.uprating
+          rounding:
+            type: nearest
+            interval: 100
+    amount:
+      2026-01-01: 290
+  - threshold:
+      values:
+        2026-01-01: 94_800
+      metadata:
+        uprating:
+          parameter: gov.irs.uprating
+          rounding:
+            type: nearest
+            interval: 100
+    amount:
+      2026-01-01: 280
+  - threshold:
+      values:
+        2026-01-01: 94_900
+      metadata:
+        uprating:
+          parameter: gov.irs.uprating
+          rounding:
+            type: nearest
+            interval: 100
+    amount:
+      2026-01-01: 270
+  - threshold:
+      values:
+        2026-01-01: 95_000
+      metadata:
+        uprating:
+          parameter: gov.irs.uprating
+          rounding:
+            type: nearest
+            interval: 100
+    amount:
+      2026-01-01: 260
+  - threshold:
+      values:
+        2026-01-01: 95_100
+      metadata:
+        uprating:
+          parameter: gov.irs.uprating
+          rounding:
+            type: nearest
+            interval: 100
+    amount:
+      2026-01-01: 250
+  - threshold:
+      values:
+        2026-01-01: 95_200
+      metadata:
+        uprating:
+          parameter: gov.irs.uprating
+          rounding:
+            type: nearest
+            interval: 100
+    amount:
+      2026-01-01: 240
+  - threshold:
+      values:
+        2026-01-01: 95_300
+      metadata:
+        uprating:
+          parameter: gov.irs.uprating
+          rounding:
+            type: nearest
+            interval: 100
+    amount:
+      2026-01-01: 230
+  - threshold:
+      values:
+        2026-01-01: 95_400
+      metadata:
+        uprating:
+          parameter: gov.irs.uprating
+          rounding:
+            type: nearest
+            interval: 100
+    amount:
+      2026-01-01: 220
+  - threshold:
+      values:
+        2026-01-01: 95_500
+      metadata:
+        uprating:
+          parameter: gov.irs.uprating
+          rounding:
+            type: nearest
+            interval: 100
+    amount:
+      2026-01-01: 210
+  - threshold:
+      values:
+        2026-01-01: 95_600
+      metadata:
+        uprating:
+          parameter: gov.irs.uprating
+          rounding:
+            type: nearest
+            interval: 100
+    amount:
+      2026-01-01: 200
+  - threshold:
+      values:
+        2026-01-01: 95_700
+      metadata:
+        uprating:
+          parameter: gov.irs.uprating
+          rounding:
+            type: nearest
+            interval: 100
+    amount:
+      2026-01-01: 190
+  - threshold:
+      values:
+        2026-01-01: 95_800
+      metadata:
+        uprating:
+          parameter: gov.irs.uprating
+          rounding:
+            type: nearest
+            interval: 100
+    amount:
+      2026-01-01: 180
+  - threshold:
+      values:
+        2026-01-01: 95_900
+      metadata:
+        uprating:
+          parameter: gov.irs.uprating
+          rounding:
+            type: nearest
+            interval: 100
+    amount:
+      2026-01-01: 170
+  - threshold:
+      values:
+        2026-01-01: 96_000
+      metadata:
+        uprating:
+          parameter: gov.irs.uprating
+          rounding:
+            type: nearest
+            interval: 100
+    amount:
+      2026-01-01: 160
+  - threshold:
+      values:
+        2026-01-01: 96_100
+      metadata:
+        uprating:
+          parameter: gov.irs.uprating
+          rounding:
+            type: nearest
+            interval: 100
+    amount:
+      2026-01-01: 150
+  - threshold:
+      values:
+        2026-01-01: 96_200
+      metadata:
+        uprating:
+          parameter: gov.irs.uprating
+          rounding:
+            type: nearest
+            interval: 100
+    amount:
+      2026-01-01: 140
+  - threshold:
+      values:
+        2026-01-01: 96_300
+      metadata:
+        uprating:
+          parameter: gov.irs.uprating
+          rounding:
+            type: nearest
+            interval: 100
+    amount:
+      2026-01-01: 130
+  - threshold:
+      values:
+        2026-01-01: 96_400
+      metadata:
+        uprating:
+          parameter: gov.irs.uprating
+          rounding:
+            type: nearest
+            interval: 100
+    amount:
+      2026-01-01: 120
+  - threshold:
+      values:
+        2026-01-01: 96_500
+      metadata:
+        uprating:
+          parameter: gov.irs.uprating
+          rounding:
+            type: nearest
+            interval: 100
+    amount:
+      2026-01-01: 110
+  - threshold:
+      values:
+        2026-01-01: 96_600
+      metadata:
+        uprating:
+          parameter: gov.irs.uprating
+          rounding:
+            type: nearest
+            interval: 100
+    amount:
+      2026-01-01: 100
+  - threshold:
+      values:
+        2026-01-01: 96_700
+      metadata:
+        uprating:
+          parameter: gov.irs.uprating
+          rounding:
+            type: nearest
+            interval: 100
+    amount:
+      2026-01-01: 90
+  - threshold:
+      values:
+        2026-01-01: 96_800
+      metadata:
+        uprating:
+          parameter: gov.irs.uprating
+          rounding:
+            type: nearest
+            interval: 100
+    amount:
+      2026-01-01: 80
+  - threshold:
+      values:
+        2026-01-01: 96_900
+      metadata:
+        uprating:
+          parameter: gov.irs.uprating
+          rounding:
+            type: nearest
+            interval: 100
+    amount:
+      2026-01-01: 70
+  - threshold:
+      values:
+        2026-01-01: 97_000
+      metadata:
+        uprating:
+          parameter: gov.irs.uprating
+          rounding:
+            type: nearest
+            interval: 100
+    amount:
+      2026-01-01: 60
+  - threshold:
+      values:
+        2026-01-01: 97_100
+      metadata:
+        uprating:
+          parameter: gov.irs.uprating
+          rounding:
+            type: nearest
+            interval: 100
+    amount:
+      2026-01-01: 50
+  - threshold:
+      values:
+        2026-01-01: 97_200
+      metadata:
+        uprating:
+          parameter: gov.irs.uprating
+          rounding:
+            type: nearest
+            interval: 100
+    amount:
+      2026-01-01: 40
+  - threshold:
+      values:
+        2026-01-01: 97_300
+      metadata:
+        uprating:
+          parameter: gov.irs.uprating
+          rounding:
+            type: nearest
+            interval: 100
+    amount:
+      2026-01-01: 30
+  - threshold:
+      values:
+        2026-01-01: 97_400
+      metadata:
+        uprating:
+          parameter: gov.irs.uprating
+          rounding:
+            type: nearest
+            interval: 100
+    amount:
+      2026-01-01: 20
+  - threshold:
+      values:
+        2026-01-01: 97_500
+      metadata:
+        uprating:
+          parameter: gov.irs.uprating
+          rounding:
+            type: nearest
+            interval: 100
+    amount:
+      2026-01-01: 10
+  - threshold:
+      values:
+        2026-01-01: 97_600
+      metadata:
+        uprating:
+          parameter: gov.irs.uprating
+          rounding:
+            type: nearest
+            interval: 100
+    amount:
+      2026-01-01: 0

policyengine_us/parameters/gov/states/ar/tax/income/rates/main/high_income/rate.yaml

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+description: Arkansas applies these marginal rates to the entire net income of a filer whose net income exceeds the high-income threshold, before subtracting the bracket adjustment.
+metadata:
+  type: marginal_rate
+  threshold_unit: currency-USD
+  rate_unit: /1
+  label: Arkansas high-income tax table
+  reference:
+  - title: A.C.A. § 26-51-201(a)(4)(B), as amended by Act 1 of 2026 (1st Extraordinary Session), § 1
+    href: https://www.arkleg.state.ar.us/Home/FTPDocument?path=%2FACTS%2F2026S1%2FPublic%2FACT1.pdf#page=2
+  - title: A.C.A. § 26-51-201(d)(1), as amended by Act 532 of 2023, § 2 (bracket amounts indexed annually, rounded to the nearest $100)
+    href: https://www.arkleg.state.ar.us/Home/FTPDocument?path=%2FACTS%2F2023R%2FPublic%2FACT532.pdf#page=4
+brackets:
+  - threshold:
+      2026-01-01: 0
+    rate:
+      2026-01-01: 0.02
+  # The statute's rows are $0-$4,700 at 2% and $4,701 and above at 3.7%, so
+  # 3.7% applies to each dollar above $4,700.
+  - threshold:
+      values:
+        2026-01-01: 4_700
+      metadata:
+        uprating:
+          parameter: gov.irs.uprating
+          rounding:
+            type: nearest
+            interval: 100
+    rate:
+      2026-01-01: 0.037

policyengine_us/parameters/gov/states/ar/tax/income/rates/main/high_income/threshold.yaml

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+description: Arkansas taxes net income above this amount under the high-income tax table, less the bracket adjustment.
+values:
+  2026-01-01: 94_700
+metadata:
+  unit: currency-USD
+  period: year
+  label: Arkansas high-income tax table threshold
+  uprating:
+    parameter: gov.irs.uprating
+    rounding:
+      type: nearest
+      interval: 100
+  reference:
+  - title: A.C.A. § 26-51-201(a)(4)(A)-(B), as amended by Act 1 of 2026 (1st Extraordinary Session), § 1
+    href: https://www.arkleg.state.ar.us/Home/FTPDocument?path=%2FACTS%2F2026S1%2FPublic%2FACT1.pdf#page=1
+  - title: A.C.A. § 26-51-201(d)(1), as amended by Act 532 of 2023, § 2 (bracket amounts indexed annually, rounded to the nearest $100)
+    href: https://www.arkleg.state.ar.us/Home/FTPDocument?path=%2FACTS%2F2023R%2FPublic%2FACT532.pdf#page=4