Use bronze premiums for selected Marketplace plans

changelog.d/changed/8211.md

@@ -0,0 +1 @@
+Use actual lowest-cost bronze premiums when Bronze is the selected Marketplace plan category.

policyengine_us/tests/policy/baseline/gov/aca/ptc/marketplace_net_premium.yaml

@@ -41,3 +41,17 @@
     selected_marketplace_plan_premium_proxy: 8_000
     used_aca_ptc: 0
     marketplace_net_premium: 8_000
+
+- name: Bronze selected plan net premium uses actual bronze premium.
+  absolute_error_margin: 0.01
+  period: 2026
+  input:
+    pays_aca_premium: true
+    selected_marketplace_plan_category: BRONZE
+    slcsp: 10_000
+    lcbp: 5_000
+    aca_ptc: 3_000
+  output:
+    selected_marketplace_plan_premium_proxy: 5_000
+    used_aca_ptc: 3_000
+    marketplace_net_premium: 2_000

policyengine_us/tests/policy/baseline/gov/aca/ptc/selected_marketplace_plan_premium_proxy.yaml

@@ -63,3 +63,26 @@
     pays_aca_premium: true
     is_aca_ptc_eligible: false
     selected_marketplace_plan_premium_proxy: 8_000
+
+- name: Case 6, bronze selected plan uses the lowest-cost bronze premium.
+  absolute_error_margin: 0.01
+  period: 2026
+  input:
+    pays_aca_premium: true
+    selected_marketplace_plan_category: BRONZE
+    slcsp: 10_000
+    lcbp: 6_500
+  output:
+    selected_marketplace_plan_premium_proxy: 6_500
+
+- name: Case 7, silver selected plan keeps the benchmark-ratio proxy.
+  absolute_error_margin: 0.01
+  period: 2026
+  input:
+    pays_aca_premium: true
+    selected_marketplace_plan_category: SILVER
+    slcsp: 10_000
+    lcbp: 6_500
+    selected_marketplace_plan_benchmark_ratio: 0.9
+  output:
+    selected_marketplace_plan_premium_proxy: 9_000

policyengine_us/tests/policy/baseline/gov/aca/ptc/used_aca_ptc.yaml

@@ -13,7 +13,7 @@
     used_aca_ptc: 200
     unused_aca_ptc: 0
 
-- name: Case 2, a bronze-like ratio leaves some ACA PTC unused.
+- name: Case 2, a lower-than-benchmark selected-plan ratio leaves some ACA PTC unused.
   absolute_error_margin: 0.01
   period: 2025
   input:
@@ -56,3 +56,21 @@
     selected_marketplace_plan_premium_proxy: 0
     used_aca_ptc: 0
     unused_aca_ptc: 200
+
+- name: Case 5, bronze selected plan uses actual bronze premium before applying PTC.
+  absolute_error_margin: 0.01
+  period: 2026
+  input:
+    is_aca_ptc_eligible: true
+    pays_aca_premium: true
+    selected_marketplace_plan_category: BRONZE
+    slcsp: 10_000
+    lcbp: 7_000
+    aca_magi: 20_000
+    aca_required_contribution_percentage: 0.04
+    tax_unit_is_filer: true
+  output:
+    aca_ptc: 9_200
+    selected_marketplace_plan_premium_proxy: 7_000
+    used_aca_ptc: 7_000
+    unused_aca_ptc: 2_200

policyengine_us/variables/gov/aca/ptc/selected_marketplace_plan_category.py

@@ -0,0 +1,15 @@
+from policyengine_us.model_api import *
+
+
+class MarketplacePlanCategory(Enum):
+    BRONZE = "Bronze"
+    SILVER = "Silver"
+
+
+class selected_marketplace_plan_category(Variable):
+    value_type = Enum
+    possible_values = MarketplacePlanCategory
+    default_value = MarketplacePlanCategory.SILVER
+    entity = TaxUnit
+    label = "Selected Marketplace plan category"
+    definition_period = YEAR

policyengine_us/variables/gov/aca/ptc/selected_marketplace_plan_premium_proxy.py

@@ -12,9 +12,17 @@ def formula(tax_unit, period, parameters):
         takes_up_aca_if_eligible = tax_unit("takes_up_aca_if_eligible", period)
         person = tax_unit.members
         pays_marketplace_premium = tax_unit.sum(person("pays_aca_premium", period)) > 0
+        category = tax_unit("selected_marketplace_plan_category", period)
+        silver_premium = tax_unit("slcsp", period) * tax_unit(
+            "selected_marketplace_plan_benchmark_ratio", period
+        )
+        selected_plan_premium = where(
+            category == category.possible_values.BRONZE,
+            tax_unit("lcbp", period),
+            silver_premium,
+        )
         return where(
             takes_up_aca_if_eligible & pays_marketplace_premium,
-            tax_unit("slcsp", period)
-            * tax_unit("selected_marketplace_plan_benchmark_ratio", period),
+            selected_plan_premium,
             0,
         )