SSI spousal deeming uses wrong FBR: couples lose /month when deeming applies (#6843)

* SSI spousal deeming uses wrong FBR: couples lose /month when deeming applies
Fixes #6842

* Fix SSI spousal deeming to correctly use couple FBR instead of individual FBR

This commit fixes a critical bug in SSI spousal deeming calculations and improves code organization:

1. **Main Fix: Use couple FBR when deeming applies**
   - Modified `ssi_amount_if_eligible.py` to use couple rate ($1,450) instead of individual rate ($967) when spousal deeming applies
   - This corrects a $483/month ($5,796/year) underpayment for couples where only one spouse is eligible and the other has income exceeding the deeming threshold
   - Added mathematical proof in comments explaining why the regulatory cap is redundant

2. **New variable: is_ssi_spousal_deeming**
   - Created helper variable to determine when spousal deeming applies (spouse's countable income > $483/month)
   - Consolidates threshold logic in one place to avoid duplication
   - Clear boolean naming convention consistent with other SSI variables

3. **Bug fix: Child allocation consistency**
   - Fixed `ssi_unearned_income_deemed_from_ineligible_spouse.py` to multiply child allocations by `is_ssi_aged_blind_disabled`
   - Now consistent with `ssi_earned_income_deemed_from_ineligible_spouse.py` and parent deeming pattern

4. **Code improvements**
   - Refactored `ssi_income_deemed_from_ineligible_spouse.py` to reuse `is_ssi_spousal_deeming` instead of duplicating threshold check
   - Eliminated nested `where()` in `ssi_amount_if_eligible.py` for better readability
   - Better variable naming: `individual_earned` instead of `indiv_earned`

5. **Test updates**
   - Updated integration test expectations to reflect correct SSI amounts with couple FBR
   - All 102 SSI tests passing

Fixes #6842

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude <[email protected]>

* minor

* Improve SSI spousal deeming implementation and add comprehensive tests

This commit refines the SSI spousal deeming fix with better code organization
and additional test coverage:

1. **Move cap logic from uncapped_ssi to ssi**
   - Makes uncapped_ssi truly "uncapped" (just amount - countable)
   - Consolidates all final logic (floor and cap) in the ssi output variable
   - Clearer separation of concerns

2. **Refactor is_ssi_spousal_deeming for clarity**
   - Use add() to combine earned and unearned deemed income
   - Rename variables for consistency (spouse_deemed_income)
   - Break out nested where() statements for readability

3. **Update comments with corrected understanding**
   - Clarify that deeming threshold compares GROSS income (not countable)
   - Explain why cap is necessary (not redundant)
   - Document that exclusions apply to COMBINED income after threshold check

4. **Add comprehensive test cases**
   - Case 8: Spouse earns $967 - demonstrates cap is necessary
   - Case 9: Spouse earns $3,000, no child - shows $0 benefit
   - Case 10: Spouse earns $3,000, with child - shows $234 benefit
   - Case 11: Single parent scenario with two children
   - All tests include detailed calculation step comments

5. **Fix child allocation consistency**
   - Added missing is_ssi_aged_blind_disabled filter to unearned income variable
   - Now consistent with earned income and parent deeming patterns

All 105 SSI tests passing.

🤖 Generated with [Claude Code](https://claude.com/claude-code)

Co-Authored-By: Claude <[email protected]>

* minor

* minor

* rename

---------

Co-authored-by: Claude <[email protected]>

Author: hua7450

changelog_entry.yaml

@@ -0,0 +1,4 @@
+- bump: patch
+  changes:
+    fixed:
+    - Fix SSI spousal deeming to correctly use couple FBR instead of individual FBR.

policyengine_us/tests/policy/baseline/gov/ssa/ssi/integration_tests.yaml

@@ -68,10 +68,12 @@
   output:
     is_ssi_eligible: [true, false, true]
     # Spouse's countable: $2,000 - $20 - $65 - $957.50 = $957.50/month = $11,490/year
-    # PolicyEngine deems all of spouse's countable income (doesn't subtract spouse allowance)
+    # Since $11,490 > $5,796 (couple - individual FBR diff), deeming applies
+    # With deeming, use couple FBR: $1,450/month = $17,400/year
     ssi_income_deemed_from_ineligible_spouse: [11_490, 0, 0]
     ssi_countable_income: [11_490, 0, 0]
-    ssi: [114, 0, 11_604]  # Adult1: $11,604 - $11,490 = $114; Child gets full FBR
+    # Adult1 SSI: $17,400 (couple FBR) - $11,490 (countable) = $5,910
+    ssi: [5_910, 0, 11_604]  # Adult1: $5,910 with couple rate; Child gets full FBR
 
 - name: Case 3 - Both adults healthy with income + disabled child
   period: 2025
@@ -217,12 +219,14 @@
   output:
     is_ssi_eligible: [true, false, true]
     # Spouse's countable: $5,000 - $20 - $65 - $2,457.50 = $2,457.50/month = $29,490/year
-    # PolicyEngine deems all countable income without subtracting spouse allowance
+    # Since $29,490 > $5,796 (couple - individual FBR diff), deeming applies
+    # With deeming, use couple FBR: $1,450/month = $17,400/year
+    # Adult1 SSI: $17,400 (couple FBR) - $29,490 (countable) = -$12,090, capped at $0
     ssi_income_deemed_from_ineligible_spouse: [29_490, 0, 0]
     # Parent income deeming to child also gets high amount
     ssi_unearned_income_deemed_from_ineligible_parent: [0, 0, 17_886]
     ssi_countable_income: [29_490, 0, 17_646]
-    ssi: [0, 0, 0]  # Both disabled members have too much deemed income
+    ssi: [0, 0, 0]  # Both disabled members have countable income exceeding FBR
 
 - name: Case 7 - Illinois single parent with $9,600 income + healthy child
   period: 2024-01
@@ -254,3 +258,145 @@
     ssi_countable_income: [357.50, 0]
     ssi_amount_if_eligible: [943, 943]
     ssi: [585.50, 0]
+
+- name: Case 8 - Deeming applies, benefit capped at individual FBR
+  period: 2025-01
+  input:
+    people:
+      adult1:
+        age: 55
+        is_disabled: false
+        employment_income: 967 * 12  # $967/month
+      adult2:
+        age: 60
+        is_disabled: true
+        employment_income: 0
+    tax_units:
+      tax_unit:
+        members: [adult1, adult2]
+    marital_units:
+      marital_unit:
+        members: [adult1, adult2]
+    households:
+      household:
+        members: [adult1, adult2]
+        state_code: NC
+  output:
+    is_ssi_eligible: [false, true]
+    # Step 1: Check if deeming applies
+    # Adult1 gross income: $967/month > $483 threshold → Deeming applies
+    #
+    # Step 2: Calculate deemed income
+    # Combined income: $967/month earned
+    # Apply exclusions: $967 - $20 (general) - $65 (earned) = $882
+    # Take half: $882 / 2 = $441/month
+    # Adult2 alone countable: $0
+    # Deemed income = $441 - $0 = $441/month
+    ssi_income_deemed_from_ineligible_spouse: [0, 441]
+    ssi_countable_income: [0, 441]
+    #
+    # Step 3: Calculate benefit
+    # Use couple FBR (deeming applies): $1,450/month
+    # Benefit before cap: $1,450 - $441 = $1,009/month
+    # Cap at individual FBR: min($1,009, $967) = $967/month
+    # Note: This demonstrates the cap is necessary when spouse's gross income
+    # is just above $483, resulting in low countable income after exclusions
+    ssi: [0, 967] 
+
+- name: Case 9 - Deeming applies without child
+  period: 2025-01
+  input:
+    people:
+      adult1:
+        age: 41
+        is_disabled: false
+        employment_income: 3_000 * 12  # $3,000/month
+      adult2:
+        age: 40
+        is_disabled: true
+        employment_income: 0
+    tax_units:
+      tax_unit:
+        members: [adult1, adult2]
+    marital_units:
+      marital_unit:
+        members: [adult1, adult2]
+    households:
+      household:
+        members: [adult1, adult2]
+        state_code: NC
+  output:
+    is_ssi_eligible: [false, true]
+    # Step 1: No child allocation (no child present)
+    # Adult1 gross income: $3,000/month (no reduction)
+    #
+    # Step 2: Check if deeming applies
+    # Adult1 gross income: $3,000 > $483 threshold → Deeming applies
+    #
+    # Step 3: Calculate deemed income
+    # Combined income: $3,000/month earned
+    # Apply exclusions: $3,000 - $20 (general) - $65 (earned) = $2,915
+    # Take half: $2,915 / 2 = $1,457.50/month
+    # Adult2 alone countable: $0
+    # Deemed income = $1,457.50 - $0 = $1,457.50/month
+    ssi_income_deemed_from_ineligible_spouse: [0, 1_457.50]
+    ssi_countable_income: [0, 1_457.50]
+    #
+    # Step 4: Calculate benefit
+    # Use couple FBR (deeming applies): $1,450/month
+    # Benefit before cap: $1,450 - $1,457.50 = -$7.50 (negative)
+    # Benefit capped at $0 (cannot be negative)
+    ssi: [0, 0]
+
+- name: Case 10 - Deeming applies with child allocation (compare to Case 9)
+  period: 2025-01
+  input:
+    people:
+      adult1:
+        age: 41
+        is_disabled: false
+        employment_income: 3_000 * 12  # $3,000/month
+      adult2:
+        age: 40
+        is_disabled: true
+        employment_income: 0
+      child:
+        age: 12
+        is_disabled: false
+        employment_income: 0
+    tax_units:
+      tax_unit:
+        members: [adult1, adult2, child]
+    marital_units:
+      marital_unit:
+        members: [adult1, adult2, child]
+    households:
+      household:
+        members: [adult1, adult2, child]
+        state_code: NC
+  output:
+    is_ssi_eligible: [false, true, false]
+    # Step 1: Apply child allocation
+    # Child allocation: $1,450 (couple FBR) - $967 (individual FBR) = $483/month
+    # Child has $0 income, so full $483 allocation applies
+    # Adult1 earned after child allocation: $3,000 - $483 = $2,517/month
+    #
+    # Step 2: Check if deeming applies
+    # Adult1 income after child allocation: $2,517 > $483 threshold → Deeming applies
+    #
+    # Step 3: Calculate deemed income
+    # Combined income: $2,517/month earned (after child allocation)
+    # Apply exclusions: $2,517 - $20 (general) - $65 (earned) = $2,432
+    # Take half: $2,432 / 2 = $1,216/month
+    # Adult2 alone countable: $0
+    # Deemed income = $1,216 - $0 = $1,216/month
+    ssi_income_deemed_from_ineligible_spouse: [0, 1_216, 0]
+    ssi_countable_income: [0, 1_216, 0]
+    #
+    # Step 4: Calculate benefit
+    # Use couple FBR (deeming applies): $1,450/month
+    # Benefit before cap: $1,450 - $1,216 = $234/month
+    # Cap at individual FBR: min($234, $967) = $234 (no cap needed)
+    # Note: Compare to Case 9 - child allocation ($483) reduces deemed income,
+    # changing result from $0 to $234/month
+    ssi: [0, 234, 0]

policyengine_us/variables/gov/ssa/ssi/eligibility/income/deemed/from_ineligible_spouse/is_ssi_spousal_deeming_applies.py

@@ -0,0 +1,41 @@
+from policyengine_us.model_api import *
+
+
+class is_ssi_spousal_deeming_applies(Variable):
+    value_type = bool
+    entity = Person
+    label = "SSI spousal deeming applies"
+    definition_period = YEAR
+    reference = "https://www.law.cornell.edu/cfr/text/20/416.1163"
+    defined_for = "is_ssi_eligible_individual"
+    documentation = """
+    Returns True when spousal deeming applies according to 20 CFR §416.1163.
+
+    Spousal deeming applies when:
+    1. Person is an eligible individual (not part of an eligible couple)
+    2. Spouse is ineligible (not aged/blind/disabled)
+    3. Spouse's leftover income (after child allocations) exceeds the difference
+       between couple FBR and individual FBR
+
+    When deeming applies, the benefit calculation uses the couple FBR instead
+    of the individual FBR, recognizing that two people have higher expenses.
+    """
+
+    def formula(person, period, parameters):
+        # Get spouse's deemed income (after child allocations)
+        spouse_deemed_income = add(
+            person,
+            period,
+            [
+                "ssi_earned_income_deemed_from_ineligible_spouse",
+                "ssi_unearned_income_deemed_from_ineligible_spouse",
+            ],
+        )
+
+        # Compare to FBR differential (couple rate - individual rate)
+        p = parameters(period).gov.ssa.ssi.amount
+        diff = (p.couple - p.individual) * MONTHS_IN_YEAR
+
+        # Deeming applies when spouse's deemed income exceeds the differential
+        # Note: regulation says "not more than" means ≤, so we use > for deeming
+        return spouse_deemed_income > diff

policyengine_us/variables/gov/ssa/ssi/eligibility/income/deemed/from_ineligible_spouse/ssi_income_deemed_from_ineligible_spouse.py

@@ -22,37 +22,37 @@ class ssi_income_deemed_from_ineligible_spouse(Variable):
     unit = USD
 
     def formula(person, period, parameters):
-        # 1. Sum leftover spouse earned/unearned (post-child allocations).
+        # 1. Check if spousal deeming applies (avoids duplicating threshold logic)
+        deeming_applies = person("is_ssi_spousal_deeming_applies", period)
+
+        # 2. If deeming applies, calculate deemed amount using "difference" approach:
+        #    (couple combined countable) - (individual alone countable)
+
+        # Get spouse's leftover income (post-child allocations)
         spouse_earned = person(
             "ssi_earned_income_deemed_from_ineligible_spouse", period
         )
         spouse_unearned = person(
             "ssi_unearned_income_deemed_from_ineligible_spouse", period
         )
-        leftover_spouse = spouse_earned + spouse_unearned
-
-        # 2. Compare leftover to FBR difference
-        p = parameters(period).gov.ssa.ssi.amount
-        diff = (p.couple - p.individual) * MONTHS_IN_YEAR
-        if_leftover_exceeds = leftover_spouse > diff
-
-        # 3. If leftover <= diff => no deeming
-        #    If leftover > diff => difference of incomes approach
-        #    (couple combined) - (individual alone).
-        #   (a) individual's own income
-        indiv_earned = person("ssi_earned_income", period)
-        indiv_unearned = person("ssi_unearned_income", period)
+
+        # Get individual's own income
+        individual_earned = person("ssi_earned_income", period)
+        individual_unearned = person("ssi_unearned_income", period)
+
+        # Calculate individual's countable income (alone)
         alone_countable = _apply_ssi_exclusions(
-            indiv_earned, indiv_unearned, parameters, period
+            individual_earned, individual_unearned, parameters, period
         )
 
-        #   (b) couple combined income
+        # Calculate couple's combined countable income
         couple_countable = _apply_ssi_exclusions(
-            indiv_earned + spouse_earned,
-            indiv_unearned + spouse_unearned,
+            individual_earned + spouse_earned,
+            individual_unearned + spouse_unearned,
             parameters,
             period,
         )
 
-        deemed_if_exceeds = max_(0, couple_countable - alone_countable)
-        return if_leftover_exceeds * deemed_if_exceeds
+        # Deemed amount is the difference (only when deeming applies)
+        deemed_amount = max_(0, couple_countable - alone_countable)
+        return deeming_applies * deemed_amount

policyengine_us/variables/gov/ssa/ssi/ssi.py

@@ -13,4 +13,25 @@ class ssi(Variable):
     def formula(person, period, parameters):
         if parameters(period).gov.ssa.ssi.abolish_ssi:
             return 0
-        return max_(0, person("uncapped_ssi", period))
+
+        uncapped = person("uncapped_ssi", period)
+
+        # Apply floor: SSI cannot be negative
+        benefit = max_(0, uncapped)
+
+        # Apply cap when spousal deeming: cannot exceed individual FBR
+        # per 20 CFR §416.1163
+        # This cap is necessary when spouse's gross income is just above $483:
+        # - Deeming applies (uses couple FBR)
+        # - After exclusions, countable may be low
+        # - Benefit could exceed individual FBR without this cap
+        deeming_applies = person("is_ssi_spousal_deeming_applies", period)
+        p = parameters(period).gov.ssa.ssi.amount
+        individual_max = p.individual * MONTHS_IN_YEAR
+        capped_benefit = min_(benefit, individual_max)
+
+        return where(
+            deeming_applies,
+            capped_benefit,
+            benefit,
+        )

policyengine_us/variables/gov/ssa/ssi/ssi_amount_if_eligible.py

@@ -12,12 +12,34 @@ class ssi_amount_if_eligible(Variable):
     def formula(person, period, parameters):
         p = parameters(period).gov.ssa.ssi.amount
         is_dependent = person("is_tax_unit_dependent", period)
+
+        # Three scenarios for adults:
+        # 1. Both spouses eligible (joint claim) → couple rate / 2
+        # 2. One eligible, no deeming → individual rate
+        # 3. One eligible, deeming applies → couple rate (capped in ssi)
+        #
+        # Note: In scenario 3, deeming applies when spouse's GROSS income > $483.
+        # Income exclusions are applied to the COMBINED income afterwards.
+        # This means countable income can be much lower than $483, and the
+        # benefit can exceed individual FBR, requiring the cap in ssi.
+
+        is_joint_claim = person("ssi_claim_is_joint", period)
+        deeming_applies = person("is_ssi_spousal_deeming_applies", period)
+
+        # Determine FBR to use based on scenario
+        individual_or_deeming_amount = where(
+            deeming_applies,
+            p.couple,  # Scenario 3: Deeming applies - use couple rate!
+            p.individual,  # Scenario 2: No deeming
+        )
+
         head_or_spouse_amount = where(
-            person("ssi_claim_is_joint", period),
-            p.couple / 2,
-            p.individual,
+            is_joint_claim,
+            p.couple / 2,  # Scenario 1: Both eligible
+            individual_or_deeming_amount,
         )
-        # Adults amount is based on whether it is a joint claim
+
+        # Adults amount is based on scenario (see above)
         # Dependents always use individual amount.
         ssi_per_month = where(
             is_dependent, p.individual, head_or_spouse_amount