Align Medicare Part B premium modeling with enrollment targets

changelog.d/8677-medicare-part-b-enrollment.changed.md

@@ -0,0 +1 @@
+Add enrollment-gated gross Medicare Part B premiums and an explicit lagged IRMAA MAGI input path.

policyengine_us/programs.yaml

@@ -906,7 +906,10 @@ programs:
     variable: is_medicare_eligible
     parameter_prefix: gov.hhs.medicare
     verified_start_year: 2024
-    notes: Includes Part A (hospital) and Part B (medical) premiums with IRMAA adjustments
+    notes: >-
+      Includes Part A (hospital) and Part B (medical) premiums with IRMAA
+      adjustments; gross Part B premium calibration should use the
+      enrollment-gated gross_medicare_part_b_premium_if_enrolled variable.
 
   # --- HUD programs ---
   - id: section_8

policyengine_us/tests/policy/baseline/gov/hhs/medicare/eligibility/income_adjusted_part_d_premium_surcharge.yaml

@@ -46,3 +46,16 @@
     takes_up_medicare_if_eligible: false
   output:
     income_adjusted_part_d_premium_surcharge: 0
+
+- name: unit test 5 - direct Medicare IRMAA MAGI input
+  period: 2025
+  input:
+    age: 65
+    filing_status: SINGLE
+    adjusted_gross_income:
+      2023: 50_000
+    tax_exempt_interest_income:
+      2023: 0
+    medicare_irmaa_magi_two_years_prior: 500_000
+  output:
+    income_adjusted_part_d_premium_surcharge: 1_029.6

policyengine_us/tests/policy/baseline/gov/hhs/medicare/test_part_b_msp_offset.py

@@ -101,6 +101,12 @@ def test_medicare_part_b_premium_is_zero_when_not_enrolled():
 
     assert sim.calculate("msp_part_b_premium_coverage", PERIOD)[0] == pytest.approx(0)
     assert sim.calculate("medicare_part_b_premium", PERIOD)[0] == pytest.approx(0)
+    assert sim.calculate("gross_medicare_part_b_premium", PERIOD)[0] == pytest.approx(
+        2_220
+    )
+    assert sim.calculate("gross_medicare_part_b_premium_if_enrolled", PERIOD)[
+        0
+    ] == pytest.approx(0)
 
 
 def test_msp_part_b_premium_coverage_scales_with_eligible_months():
@@ -292,3 +298,87 @@ def test_gross_medicare_part_b_premium_handles_direct_filing_status_inputs():
     assert result[0] == pytest.approx(7_546.8)
     assert result[1] == pytest.approx(7_546.8)
     assert result[2] == pytest.approx(2_220)
+
+
+def test_gross_medicare_part_b_premium_if_enrolled_preserves_irmaa():
+    sim = make_simulation(
+        medicare_enrolled=True,
+        gross_part_b_premium=4_440,
+        base_part_b_premium=2_220,
+        msp_income_eligible=False,
+        msp_asset_eligible=False,
+    )
+
+    assert sim.calculate("gross_medicare_part_b_premium_if_enrolled", PERIOD)[
+        0
+    ] == pytest.approx(4_440)
+    assert sim.calculate("medicare_cost", PERIOD)[0] == pytest.approx(10_060)
+
+
+def test_medicare_irmaa_magi_two_years_prior_falls_back_to_lagged_income():
+    sim = Simulation(
+        tax_benefit_system=SYSTEM,
+        situation={
+            "people": {
+                "person": {
+                    "age": {PERIOD: 65},
+                    "base_part_b_premium": {PERIOD: 2_220},
+                    "is_medicare_eligible": {PERIOD: True},
+                    "tax_exempt_interest_income": {"2023": 6_002},
+                }
+            },
+            "households": {"household": {"members": ["person"]}},
+            "tax_units": {
+                "tax_unit": {
+                    "members": ["person"],
+                    "filing_status": {PERIOD: "SINGLE"},
+                    "adjusted_gross_income": {"2023": 100_000},
+                }
+            },
+            "spm_units": {"spm_unit": {"members": ["person"]}},
+            "families": {"family": {"members": ["person"]}},
+            "marital_units": {"marital_unit": {"members": ["person"]}},
+        },
+    )
+
+    assert sim.calculate("medicare_irmaa_magi_two_years_prior", PERIOD)[
+        0
+    ] == pytest.approx(106_002)
+    assert sim.calculate("gross_medicare_part_b_premium", PERIOD)[0] == pytest.approx(
+        3_108
+    )
+
+
+def test_medicare_irmaa_magi_two_years_prior_input_drives_irmaa():
+    sim = Simulation(
+        tax_benefit_system=SYSTEM,
+        situation={
+            "people": {
+                "person": {
+                    "age": {PERIOD: 65},
+                    "base_part_b_premium": {PERIOD: 2_220},
+                    "is_medicare_eligible": {PERIOD: True},
+                    "tax_exempt_interest_income": {"2023": 0},
+                }
+            },
+            "households": {"household": {"members": ["person"]}},
+            "tax_units": {
+                "tax_unit": {
+                    "members": ["person"],
+                    "filing_status": {PERIOD: "SINGLE"},
+                    "adjusted_gross_income": {"2023": 50_000},
+                    "medicare_irmaa_magi_two_years_prior": {PERIOD: 500_000},
+                }
+            },
+            "spm_units": {"spm_unit": {"members": ["person"]}},
+            "families": {"family": {"members": ["person"]}},
+            "marital_units": {"marital_unit": {"members": ["person"]}},
+        },
+    )
+
+    assert sim.calculate("medicare_irmaa_magi_two_years_prior", PERIOD)[
+        0
+    ] == pytest.approx(500_000)
+    assert sim.calculate("gross_medicare_part_b_premium", PERIOD)[0] == pytest.approx(
+        7_546.8
+    )

policyengine_us/variables/gov/hhs/medicare/costs/medicare_cost.py

@@ -21,10 +21,11 @@ def formula(person, period, parameters):
             period
         ).calibration.gov.hhs.medicare.per_capita_cost
 
-        # Premium offsets to Medicare program cost. Use gross Part B premiums
-        # before MSP offsets so MSP support does not inflate Medicare's value.
+        # Premium offsets to Medicare program cost. Use the enrollment-gated
+        # gross Part B premium before MSP offsets so MSP support does not
+        # inflate Medicare's value.
         part_a_premium = person("base_part_a_premium", period)
-        part_b_premium = person("gross_medicare_part_b_premium", period)
+        part_b_premium = person("gross_medicare_part_b_premium_if_enrolled", period)
         total_premiums = part_a_premium + part_b_premium
 
         # Net benefit = spending - premiums

policyengine_us/variables/gov/hhs/medicare/eligibility/medicare_irmaa_magi_two_years_prior.py

@@ -0,0 +1,26 @@
+from policyengine_us.model_api import *
+
+
+class medicare_irmaa_magi_two_years_prior(Variable):
+    value_type = float
+    entity = TaxUnit
+    label = "Medicare IRMAA MAGI from two years prior"
+    unit = USD
+    definition_period = YEAR
+    reference = "https://www.law.cornell.edu/uscode/text/42/1395r"
+    documentation = (
+        "Modified adjusted gross income used to determine Medicare IRMAA "
+        "charges. Callers may provide this value directly for the current "
+        "benefit year. When it is not provided, PolicyEngine computes it as "
+        "adjusted gross income plus tax-exempt interest from two years prior. "
+        "Single-year datasets without lagged income inputs therefore default "
+        "to the modeled prior-year values, which may be zero."
+    )
+
+    def formula(tax_unit, period, parameters):
+        prior_period = period.offset(-2, "year")
+        return add(
+            tax_unit,
+            prior_period,
+            ["adjusted_gross_income", "tax_exempt_interest_income"],
+        )

policyengine_us/variables/gov/hhs/medicare/eligibility/part_b/gross_medicare_part_b_premium.py

@@ -21,12 +21,7 @@ def formula(person, period, parameters):
         is_head_of_household = filing_status == status.HEAD_OF_HOUSEHOLD
         is_surviving_spouse = filing_status == status.SURVIVING_SPOUSE
         is_separated = filing_status == status.SEPARATE
-        # Medicare Part B IRMAA is based on MAGI from 2 years prior.
-        # MAGI = AGI + tax-exempt interest.
-        prior_period = period.offset(-2, "year")
-        agi = tax_unit("adjusted_gross_income", prior_period)
-        tax_exempt_interest = tax_unit("tax_exempt_interest_income", prior_period)
-        magi = agi + tax_exempt_interest
+        magi = tax_unit("medicare_irmaa_magi_two_years_prior", period)
         base = person("base_part_b_premium", period)
 
         p = parameters(period).gov.hhs.medicare.part_b.irmaa

policyengine_us/variables/gov/hhs/medicare/eligibility/part_b/gross_medicare_part_b_premium_if_enrolled.py

@@ -0,0 +1,20 @@
+from policyengine_us.model_api import *
+
+
+class gross_medicare_part_b_premium_if_enrolled(Variable):
+    value_type = float
+    entity = Person
+    label = "Gross Medicare Part B premium if enrolled"
+    unit = USD
+    definition_period = YEAR
+    defined_for = "medicare_enrolled"
+    reference = "https://www.medicare.gov/your-medicare-costs/part-b-costs"
+    documentation = (
+        "Annual Medicare Part B premium for enrolled beneficiaries before "
+        "Medicare Savings Program coverage, including any income-related "
+        "monthly adjustment amount. Use this enrollment-gated gross premium "
+        "for CMS premiums-from-enrollees calibration targets."
+    )
+
+    def formula(person, period, parameters):
+        return person("gross_medicare_part_b_premium", period)

policyengine_us/variables/gov/hhs/medicare/eligibility/part_d/income_adjusted_part_d_premium_surcharge.py

@@ -14,10 +14,7 @@ class income_adjusted_part_d_premium_surcharge(Variable):
     def formula(person, period, parameters):
         tax_unit = person.tax_unit
         filing_status = tax_unit("filing_status", period)
-        prior_period = period.offset(-2, "year")
-        agi = tax_unit("adjusted_gross_income", prior_period)
-        tax_exempt_interest = tax_unit("tax_exempt_interest_income", prior_period)
-        magi = agi + tax_exempt_interest
+        magi = tax_unit("medicare_irmaa_magi_two_years_prior", period)
 
         status = filing_status.possible_values
         statuses = [