renaming variables and parameters

Fixes PolicyEngine#4495

changelog_entry.yaml

@@ -0,0 +1,4 @@
+- bump: minor
+  changes:
+    added:
+    - Add Montana taxable social security benefits.

policyengine_us/parameters/gov/states/mt/tax/income/social_security/amount/higher.yaml

@@ -0,0 +1,23 @@
+description: Montana uses this amount when calculating the taxable social security benefits, based on filing status.
+metadata:
+  period: year
+  unit: currency-USD
+  label: Montana social security benefits amount
+  breakdown:
+    - filing_status
+  reference:
+    - title: 2021 Montana Individual Income Tax Return (Taxable Social Security Benefits Schedule)
+      href: https://mtrevenue.gov/wp-content/uploads/mdocs/form%202%202021.pdf#page=6
+    - title: 2022 Montana Individual Income Tax Return (Taxable Social Security Benefits Schedule)
+      href: https://mtrevenue.gov/wp-content/uploads/dlm_uploads/2023/05/Montana-Idividiual-Income-Tax-Return-Form-2-2022v6.2.pdf#page=6
+    - title: 2023 Montana Individual Income Tax Return (Taxable Social Security Benefits Schedule)
+      href: https://mtrevenue.gov/wp-content/uploads/dlm_uploads/2023/12/Form_2_2023.pdf#page=6
+      # These values only appear in the tax form
+SINGLE:
+  2021-01-01: 25_000
+HEAD_OF_HOUSEHOLD:
+  2021-01-01: 25_000
+JOINT:
+  2021-01-01: 32_000
+SEPARATE:
+  2021-01-01: 16_000 

policyengine_us/parameters/gov/states/mt/tax/income/social_security/amount/lower.yaml

@@ -0,0 +1,23 @@
+description: Montana uses this amount when calculating the taxable social security benefits, based on filing status.
+metadata:
+  period: year
+  unit: currency-USD
+  label: Montana social security benefits amount
+  breakdown:
+    - filing_status
+  reference:
+    - title: 2021 Montana Individual Income Tax Return (Taxable Social Security Benefits Schedule)
+      href: https://mtrevenue.gov/wp-content/uploads/mdocs/form%202%202021.pdf#page=6
+    - title: 2022 Montana Individual Income Tax Return (Taxable Social Security Benefits Schedule)
+      href: https://mtrevenue.gov/wp-content/uploads/dlm_uploads/2023/05/Montana-Idividiual-Income-Tax-Return-Form-2-2022v6.2.pdf#page=6
+    - title: 2023 Montana Individual Income Tax Return (Taxable Social Security Benefits Schedule)
+      href: https://mtrevenue.gov/wp-content/uploads/dlm_uploads/2023/12/Form_2_2023.pdf#page=6
+      # These values only appear in the tax form
+SINGLE:
+  2021-01-01: 9_000
+HEAD_OF_HOUSEHOLD:
+  2021-01-01: 9_000
+JOINT:
+  2021-01-01: 12_000
+SEPARATE:
+  2021-01-01: 6_000 

policyengine_us/parameters/gov/states/mt/tax/income/social_security/rate/higher.yaml

@@ -0,0 +1,16 @@
+description: Montana matches this fraction of social security benefits.
+values:
+  2021-01-01: 0.85
+
+metadata:
+  unit: /1
+  period: year
+  label: Montana social security benefits rate
+  reference:
+    - title: 2021 Montana Individual Income Tax Return (Taxable Social Security Benefits Schedule)
+      href: https://mtrevenue.gov/wp-content/uploads/mdocs/form%202%202021.pdf#page=6
+    - title: 2022 Montana Individual Income Tax Return (Taxable Social Security Benefits Schedule)
+      href: https://mtrevenue.gov/wp-content/uploads/dlm_uploads/2023/05/Montana-Idividiual-Income-Tax-Return-Form-2-2022v6.2.pdf#page=6
+    - title: 2023 Montana Individual Income Tax Return (Taxable Social Security Benefits Schedule)
+      href: https://mtrevenue.gov/wp-content/uploads/dlm_uploads/2023/12/Form_2_2023.pdf#page=6
+      # This rate only appears in the tax form

policyengine_us/parameters/gov/states/mt/tax/income/social_security/rate/lower.yaml

@@ -0,0 +1,16 @@
+description: Montana matches this fraction of social security benefits. 
+values:
+  2021-01-01: 0.5
+
+metadata:
+  unit: /1
+  period: year
+  label: Montana social security benefits rate
+  reference:
+    - title: 2021 Montana Individual Income Tax Return (Taxable Social Security Benefits Schedule)
+      href: https://mtrevenue.gov/wp-content/uploads/mdocs/form%202%202021.pdf#page=6
+    - title: 2022 Montana Individual Income Tax Return (Taxable Social Security Benefits Schedule)
+      href: https://mtrevenue.gov/wp-content/uploads/dlm_uploads/2023/05/Montana-Idividiual-Income-Tax-Return-Form-2-2022v6.2.pdf#page=6
+    - title: 2023 Montana Individual Income Tax Return (Taxable Social Security Benefits Schedule)
+      href: https://mtrevenue.gov/wp-content/uploads/dlm_uploads/2023/12/Form_2_2023.pdf#page=6
+      # This rate only appears in the tax form 

policyengine_us/variables/gov/states/mt/tax/income/mt_taxable_social_security.py

@@ -3,49 +3,71 @@
 
 class mt_taxable_social_security(Variable):
     value_type = float
-    entity = TaxUnit 
+    entity = TaxUnit
     label = "Montana taxable social security benefits"
     defined_for = StateCode.MT
     definition_period = YEAR
     reference = "https://mtrevenue.gov/wp-content/uploads/mdocs/form%202%202021.pdf#page=6"
 
     def formula(tax_unit, period, parameters):
         p = parameters(period).gov.states.mt.tax.income.social_security
+        # Compute the amount based on the schedule in tax form.
         # line 1&2: 6a in tax form ?
-        social_security_benefit = tax_unit("social_security",period)
-        fraction_of_social_security_benefit= social_security_benefit*p.rate1
-        # line 3
-        tax_unit("total_income",period) - tax_unit("taxable_social_security",period)
-        # line 4: Additions Schedule line 15 - line 3 
-        0
-        # line 5: 
-        tax_emempt_interest_income = tax_unit("tax_exempt_interest_income",period) 
+        social_security = tax_unit("social_security", period)
+        social_security_benefits_fraction = social_security * p.rate.lower
+        # line 3 total_income - taxable_social_security
+        # line 4: Additions Schedule line 15 - line 3  (0?)
+        # line 5:
+        tax_emempt_interest_income = tax_unit(
+            "tax_exempt_interest_income", period
+        )
         # line 6: line 2+3+4+5
-        line_6 = fraction_of_social_security_benefit + tax_unit("total_income",period) - tax_unit("taxable_social_security",period) +tax_emempt_interest_income
-        us_ald = tax_unit("above_the_line_deductions",period) - tax_unit("student_loan_interest", period) 
+        new_total_income = (
+            social_security_benefits_fraction
+            + tax_unit("total_income", period)
+            - tax_unit("taxable_social_security", period)
+            + tax_emempt_interest_income
+        )
+        us_ald_exclue_stduent_loan = tax_unit(
+            "above_the_line_deductions", period
+        ) - tax_unit("student_loan_interest", period)
         # line 8
         person = tax_unit.members
-        line_8 = person("mt_subtractions", period) + us_ald
-        # line 9: line 8 -line 6, if line 8 >= line 6, return 0 
-        line_9 = max(0, line_8 - line_6)
+        increased_subtractions = (
+            person("mt_subtractions", period) + us_ald_exclue_stduent_loan
+        )
+        # line 9: line 6 -line 8, if line 8 >= line 6, return 0
+        remaining_income = max(0, new_total_income - increased_subtractions)
         # line 10: get amount based on filing status
-        amount_1 = p.social_security.amount1[filing_status] 
+        amount_higher = p.social_security.amount.higher[filing_status]
+        # line 11: line 9 - line 10
         # line 12: get amount based on filing status
-        amount_2 = p.social_security.amount2[filing_status]
-        # lien 13: line 11 - line 12 
-        line_13 = max(0,amount_1 - line_9 - amount_2)
+        amount_lower = p.social_security.amount.lower[filing_status]
+        # lien 13: line 11 - line 12
+        minimum_tax_threshold = max_(
+            0, amount_higher - remaining_income - amount_lower
+        )
         # line 14 & 15
-        line_15 = min(amount_1 - line_9,amount_2)*p.rate1
+        minimum_tax_threshold_fraction = (
+            min_(amount_higher - remaining_income, amount_lower) * p.rate.lower
+        )
         # line 16
-        line_16 = min(line_15,fraction_of_social_security_benefit)
+        minimum_fraction = min_(
+            minimum_tax_threshold_fraction, social_security_benefits_fraction
+        )
         # line 17 & 18 ## line_13*p.rate2 + line_16
-        # line 19 ## social_security_benefit*p.rate2
-        # line 20 
-        lesser_of_18_or_19 = min(social_security_benefit*p.rate2, line_13*p.rate2 + line_16)
-        # line 11: line 10 - line 9, if line 10 >= line 9, return 0 
+        adjusted_tax_amount = (
+            minimum_tax_threshold * p.rate.higher + minimum_fraction
+        )
+        # line 19 ## line_1*p.rate2
+        adjusted_taxable_amount = social_security * p.rate.higher
+        # line 20
+        lesser_of_taxable_amount = min_(
+            adjusted_taxable_amount, adjusted_tax_amount
+        )
+        # line 11: line 9 - line 10, if line 10 >= line 9, return 0. Else, proceed line 12 through 20
         return select(
-                amount_1 < line_9,
-                lesser_of_18_or_19,
+            amount_higher < remaining_income,
+            lesser_of_taxable_amount,
             default=0,
         )
-