Added Montana Interest Exemptions

Fixes #3058

changelog_entry.yaml

@@ -0,0 +1,4 @@
+- bump: minor
+  changes:
+    added:
+    - Montana interest exemptions.

policyengine_us/parameters/gov/states/mt/tax/income/exemptions/age.yaml

@@ -0,0 +1,12 @@
+description: Montana allows single filers to receive partial interest exemption at or above the following older age threshold. 
+metadata:
+  label: Montana partial interest exemption age eligibility
+  period: year
+  unit: year
+  reference:
+  - title: 2022 Montana Form 2 | line 3 - Partial Interest Exemption for Taxpayers
+    href: https://mtrevenue.gov/wp-content/uploads/dlm_uploads/2022/12/Form-2-2022-Instructions.pdf#page=25
+  - title: Administrative Rules of Montana | Income Taxes | § 42.14.215
+    href: https://advance.lexis.com/documentpage/?pdmfid=1000516&crid=fb5db531-a80f-4790-bddb-eefc8327ef60&config=00JAA1MDBlYzczZi1lYjFlLTQxMTgtYWE3OS02YTgyOGM2NWJlMDYKAFBvZENhdGFsb2feed0oM9qoQOMCSJFX5qkd&pddocfullpath=%2Fshared%2Fdocument%2Fstatutes-legislation%2Furn%3AcontentItem%3A65D2-CDH3-CGX8-044N-00008-00&pdcontentcomponentid=234186&pdteaserkey=sr1&pditab=allpods&ecomp=8s65kkk&earg=sr1&prid=66f02b0a-c5ae-4162-9535-127751546807
+values:
+  2021-01-01: 65

policyengine_us/parameters/gov/states/mt/tax/income/exemptions/amount.yaml

@@ -0,0 +1,31 @@
+description: Montana provides partial interest exemption for the age filer at this amount.
+metadata:
+  label: Montana interest exemption base amount
+  period: year
+  unit: currency-USD
+  breakdown:
+  - filing_status
+  reference: 
+  - title: 2022 Montana Form 2 | line 3 - Partial Interest Exemption for Taxpayers
+    href: https://mtrevenue.gov/wp-content/uploads/dlm_uploads/2022/12/Form-2-2022-Instructions.pdf#page=25
+  - title: Administrative Rules of Montana | Income Taxes | § 42.14.215
+    href: https://advance.lexis.com/documentpage/?pdmfid=1000516&crid=fb5db531-a80f-4790-bddb-eefc8327ef60&config=00JAA1MDBlYzczZi1lYjFlLTQxMTgtYWE3OS02YTgyOGM2NWJlMDYKAFBvZENhdGFsb2feed0oM9qoQOMCSJFX5qkd&pddocfullpath=%2Fshared%2Fdocument%2Fstatutes-legislation%2Furn%3AcontentItem%3A65D2-CDH3-CGX8-044N-00008-00&pdcontentcomponentid=234186&pdteaserkey=sr1&pditab=allpods&ecomp=8s65kkk&earg=sr1&prid=66f02b0a-c5ae-4162-9535-127751546807
+SINGLE:
+  2021-01-01: 800 # 2021 need to update 
+  2022-01-01: 800
+SEPARATE:
+  2021-01-01: 800
+  2022-01-01: 800
+JOINT:
+  2021-01-01: 1_600
+  2022-01-01: 1_600
+HEAD_OF_HOUSEHOLD:
+  2021-01-01: 800
+  2022-01-01: 800
+WIDOW: # if filling status on federal form is qualifing widow, we can use head of household
+  2021-01-01: 800
+  2022-01-01: 800
+
+# exemption for dependents?? should we included?
+# page15
+

policyengine_us/tests/policy/baseline/gov/states/mt/tax/income/exemptions/mt_interest_exemption.yaml

@@ -0,0 +1,31 @@
+- name: Joint filing
+  period: 2023
+  input:
+    taxsim_dividends: 1_900
+    filing_status: JOINT
+    age_head: 65
+    age_spouse: 65
+    state_code: MT
+  output:
+    mt_exemptions: 1_600
+
+- name: Joint filing
+  period: 2023
+  input:
+    taxsim_dividends: 1_900
+    filing_status: JOINT
+    age_head: 65
+    age_spouse: 62
+    state_code: MT
+  output:
+    mt_exemptions: 1_600
+
+- name: Single filing
+  period: 2023
+  input:
+    taxsim_dividends: 1_900
+    filing_status: JOINT
+    age_head: 62
+    state_code: MT
+  output:
+    mt_exemptions: 0

policyengine_us/variables/gov/states/mt/tax/income/exemptions/mt_interest.py

@@ -0,0 +1,26 @@
+from policyengine_us.model_api import *
+
+
+class mt_exemptions(Variable):
+    value_type = float
+    entity = TaxUnit
+    label = "Montana exemptions amount"
+    unit = USD
+    definition_period = YEAR
+    reference = "https://mtrevenue.gov/wp-content/uploads/dlm_uploads/2022/12/Form-2-2022-Instructions.pdf#page=25"
+    defined_for = StateCode.MT
+
+    def formula(tax_unit, period, parameters):
+        p = parameters(period).gov.states.mt.tax.income.exemptions
+        filing_status = tax_unit("filing_status", period)
+        cap_amount = p.amount[filing_status]
+        dividend_income = tax_unit(
+            "taxsim_dividends", period
+        )  # dividends or share accounts
+        qalified_amount = min_(cap_amount, dividend_income)
+        age_head = tax_unit("age_head", period)
+        eligible_aged_head = age_head >= p.age
+        age_spouse = tax_unit("age_spouse", period)
+        eligible_aged_spouse = age_spouse >= p.age
+        eligible_tax_unit = eligible_aged_head | eligible_aged_spouse
+        return where(eligible_tax_unit, qalified_amount, 0)