diff --git a/changelog.d/ssi-monthly-ism-state-readers.fixed.md b/changelog.d/ssi-monthly-ism-state-readers.fixed.md
new file mode 100644
index 00000000000..4d67fa4f3bf
--- /dev/null
+++ b/changelog.d/ssi-monthly-ism-state-readers.fixed.md
@@ -0,0 +1 @@
+Count each month's SSI in-kind support and maintenance in Maryland PAA income and in California's supplement for a couple with one SSI and one CAPI spouse. Read each month's SSI couple status and income deemed from an ineligible spouse in Maryland PAA income.
diff --git a/policyengine_us/tests/core/test_ssi_monthly_state_readers.py b/policyengine_us/tests/core/test_ssi_monthly_state_readers.py
new file mode 100644
index 00000000000..271c224362e
--- /dev/null
+++ b/policyengine_us/tests/core/test_ssi_monthly_state_readers.py
@@ -0,0 +1,265 @@
+"""Check Maryland PAA and California SSP against changes to one month's ISM."""
+
+import numpy as np
+import pytest
+from hypothesis import given, settings
+from hypothesis import strategies as st
+
+from policyengine_core.periods import period as make_period
+from policyengine_us import Simulation
+from policyengine_us.system import system
+from policyengine_us.variables.gov.ssa.ssi.eligibility.income._apply_ssi_exclusions import (
+    _apply_ssi_exclusions,
+)
+
+
+YEAR = "2024"
+MONTHS = tuple(f"{YEAR}-{month:02d}" for month in range(1, 13))
+VARIABLES = (
+    "md_paa_countable_income",
+    "md_paa_imputed_federal_ssi",
+    "md_paa",
+    "ca_state_supplement_person",
+)
+
+
+def _situation(profiles, annual_earned, annual_unearned):
+    situation = {
+        group: {}
+        for group in (
+            "people",
+            "households",
+            "tax_units",
+            "marital_units",
+            "families",
+            "spm_units",
+        )
+    }
+    rows = {}
+    for name, profile in profiles.items():
+        for state, citizenship in (
+            ("MD", "CITIZEN"),
+            ("MD", "LEGAL_PERMANENT_RESIDENT"),
+            ("CA", "CITIZEN"),
+        ):
+            unit = f"{name}_{state}_{citizenship}"
+            person = f"{unit}_head"
+            members = [person]
+            rows[name, state, citizenship] = len(situation["people"])
+            values = {
+                "age": {YEAR: 70},
+                "is_tax_unit_head": {YEAR: True},
+                "immigration_status": {YEAR: citizenship},
+                "is_ssi_qualified_noncitizen": {YEAR: False},
+                "ssi_earned_income": {YEAR: annual_earned},
+                "ssi_unearned_income": {YEAR: annual_unearned},
+                "ssi_in_kind_support_and_maintenance": dict(zip(MONTHS, profile)),
+            }
+            if state == "MD":
+                values.update(
+                    md_paa_eligible={YEAR: True},
+                    md_paa_total_cost_of_care={YEAR: 18_000},
+                )
+            else:
+                # Hold federal SSI and the couple's income fixed to isolate
+                # the supplement's own-income reader for a CAPI spouse.
+                values.update(
+                    ssi={YEAR: 7_200},
+                    ssi_countable_income={YEAR: 0},
+                )
+            situation["people"][person] = values
+            if state == "CA":
+                spouse = f"{unit}_spouse"
+                members.append(spouse)
+                situation["people"][spouse] = {
+                    "age": {YEAR: 68},
+                    "is_tax_unit_spouse": {YEAR: True},
+                    "immigration_status": {YEAR: "LEGAL_PERMANENT_RESIDENT"},
+                    "ssi_qualifying_quarters_earnings": {YEAR: 39},
+                    "ssi_countable_income": {YEAR: 0},
+                }
+            for group in (
+                "households",
+                "tax_units",
+                "marital_units",
+                "families",
+                "spm_units",
+            ):
+                situation[group][unit] = {"members": members}
+            situation["households"][unit].update(
+                state_code={YEAR: state},
+                living_arrangements_allow_for_food_preparation={YEAR: True},
+            )
+    return situation, rows
+
+
+def _monthly(simulation, variable):
+    return np.stack([simulation.calculate(variable, month) for month in MONTHS])
+
+
+@settings(max_examples=8, deadline=None, database=None, derandomize=True)
+@given(
+    ism=st.integers(20, 200),
+    extra=st.integers(1, 100),
+    annual_earned=st.integers(0, 1_200),
+    annual_unearned=st.integers(0, 2_400),
+)
+def test_state_readers_keep_a_december_ism_change_in_december(
+    ism, extra, annual_earned, annual_unearned
+):
+    situation, rows = _situation(
+        {"constant": [ism] * 12, "changed": [ism] * 11 + [ism + extra]},
+        annual_earned,
+        annual_unearned,
+    )
+    simulation = Simulation(tax_benefit_system=system, situation=situation)
+    results = {name: _monthly(simulation, name) for name in VARIABLES}
+
+    for name, values in results.items():
+        assert np.all(values >= 0)
+        np.testing.assert_allclose(
+            simulation.calculate(name, YEAR), values.sum(axis=0), atol=0.01
+        )
+        for state, citizenship in (
+            ("MD", "CITIZEN"),
+            ("MD", "LEGAL_PERMANENT_RESIDENT"),
+            ("CA", "CITIZEN"),
+        ):
+            constant = rows["constant", state, citizenship]
+            changed = rows["changed", state, citizenship]
+            np.testing.assert_allclose(
+                values[:11, constant], values[:11, changed], atol=0.01
+            )
+
+    for citizenship in ("CITIZEN", "LEGAL_PERMANENT_RESIDENT"):
+        constant = rows["constant", "MD", citizenship]
+        changed = rows["changed", "MD", citizenship]
+        countable = results["md_paa_countable_income"][-1]
+        # ISM already uses the whole $20 exclusion, so each extra dollar
+        # increases this month's countable income by one dollar.
+        assert countable[changed] - countable[constant] == pytest.approx(
+            extra, abs=0.01
+        )
+        imputed = results["md_paa_imputed_federal_ssi"][-1]
+        payment = results["md_paa"][-1]
+        if citizenship == "CITIZEN":
+            assert imputed[constant] - imputed[changed] == pytest.approx(
+                extra, abs=0.01
+            )
+            # Federal SSI offsets the income change while both amounts
+            # remain below the federal benefit rate.
+            assert payment[changed] == pytest.approx(payment[constant], abs=0.01)
+        else:
+            assert imputed[constant] == imputed[changed] == 0
+            assert payment[constant] - payment[changed] == pytest.approx(
+                extra, abs=0.01
+            )
+
+    constant = rows["constant", "CA", "CITIZEN"]
+    changed = rows["changed", "CA", "CITIZEN"]
+    payment = results["ca_state_supplement_person"][-1]
+    assert payment[constant] - payment[changed] == pytest.approx(extra, abs=0.011)
+
+
+@settings(max_examples=6, deadline=None, database=None, derandomize=True)
+@given(
+    ism=st.integers(0, 400),
+    annual_earned=st.integers(0, 24_000),
+    annual_unearned=st.integers(0, 12_000),
+)
+def test_constant_ism_keeps_the_annual_exclusion_result(
+    ism, annual_earned, annual_unearned
+):
+    situation, rows = _situation(
+        {"constant": [ism] * 12}, annual_earned, annual_unearned
+    )
+    simulation = Simulation(tax_benefit_system=system, situation=situation)
+    # Constant monthly income must retain the existing annual computation.
+    annual_countable = _apply_ssi_exclusions(
+        np.array([annual_earned]),
+        np.array([annual_unearned + 12 * ism]),
+        simulation.tax_benefit_system.parameters,
+        make_period(YEAR),
+    )[0]
+    countable = annual_countable / 12
+    for citizenship in ("CITIZEN", "LEGAL_PERMANENT_RESIDENT"):
+        index = rows["constant", "MD", citizenship]
+        np.testing.assert_allclose(
+            _monthly(simulation, "md_paa_countable_income")[:, index],
+            countable,
+            atol=0.01,
+        )
+
+    index = rows["constant", "CA", "CITIZEN"]
+    payment = _monthly(simulation, "ca_state_supplement_person")[:, index]
+    # POMS SI 01415.056 B.2.a gives the 2024 aged standard of $1,182.94.
+    # Federal administration rounds a positive balance and pays at least $1.
+    # https://secure.ssa.gov/apps10/poms.nsf/lnx/0501415056
+    balance = max(1_182.94 - 600 - countable, 0)
+    if balance == 0:
+        np.testing.assert_allclose(payment, 0, atol=0.01)
+    else:
+        assert np.all(payment >= min(balance, 1))
+        np.testing.assert_allclose(payment, max(balance, 1), atol=0.011)
+
+
+def _maryland_reference_countable(monthly_earned, monthly_unearned):
+    # Maryland DHS deducts $20 from unearned income, then $65 and one-half
+    # of the remaining earned income. When unearned income falls short of
+    # $20, DHS applies the unused part to earnings (PAA Manual 900). Under
+    # COMAR 07.03.07.08(A), DHS takes these disregards "in any month".
+    # https://dhs.maryland.gov/documents/FIA/Manuals/Public%20Assistance%20to%20Adults%20%28PAA%29%20Manual/PAA%20900%20Calculation%20of%20Benefits%20rev%2011.22.docx
+    # https://regs.maryland.gov/us/md/exec/comar/07.03.07.08
+    general = min(20, monthly_unearned)
+    return monthly_unearned - general + max(monthly_earned - 65 - (20 - general), 0) / 2
+
+
+@settings(max_examples=5, deadline=None, database=None, derandomize=True)
+@given(
+    ism=st.integers(0, 19),
+    extra=st.integers(1, 19),
+    annual_earned=st.integers(0, 2_400),
+)
+def test_state_readers_keep_a_small_ism_exclusion_in_its_month(
+    ism, extra, annual_earned
+):
+    # With ISM under $20 and no other unearned income, the unused part of
+    # the $20 exclusion reduces that month's earnings and no other month's.
+    profiles = {"constant": [ism] * 12, "changed": [ism] * 11 + [ism + extra]}
+    situation, rows = _situation(profiles, annual_earned, 0)
+    simulation = Simulation(tax_benefit_system=system, situation=situation)
+    countable = _monthly(simulation, "md_paa_countable_income")
+    supplement = _monthly(simulation, "ca_state_supplement_person")
+
+    for name, profile in profiles.items():
+        expected = [
+            _maryland_reference_countable(annual_earned / 12, monthly_ism)
+            for monthly_ism in profile
+        ]
+        for citizenship in ("CITIZEN", "LEGAL_PERMANENT_RESIDENT"):
+            np.testing.assert_allclose(
+                countable[:, rows[name, "MD", citizenship]], expected, atol=0.01
+            )
+
+    constant = rows["constant", "CA", "CITIZEN"]
+    changed = rows["changed", "CA", "CITIZEN"]
+    np.testing.assert_allclose(
+        supplement[:11, constant], supplement[:11, changed], atol=0.01
+    )
+    # SSA applies the same exclusions to this person's own income in each
+    # month (20 CFR 416.1112(c)). In December, as in every other month, it
+    # pays the 2024 aged standard of $1,182.94, less $600 of SSI and that
+    # month's countable income, rounded up to the cent. For example, $10 of
+    # ISM and $200 of earnings leave 0 + (200 - 65 - 10) / 2 = $62.50
+    # countable and a $520.44 payment; a December ISM of $25 leaves
+    # (25 - 20) + (200 - 65) / 2 = $72.50 and a $510.44 payment.
+    for name, profile in profiles.items():
+        expected = [
+            1_182.94
+            - 600
+            - _maryland_reference_countable(annual_earned / 12, monthly_ism)
+            for monthly_ism in profile
+        ]
+        np.testing.assert_allclose(
+            supplement[:, rows[name, "CA", "CITIZEN"]], expected, atol=0.011
+        )
diff --git a/policyengine_us/tests/policy/baseline/gov/states/ca/cdss/state_supplement/ca_state_supplement.yaml b/policyengine_us/tests/policy/baseline/gov/states/ca/cdss/state_supplement/ca_state_supplement.yaml
index 85dc3480892..130345be6dd 100644
--- a/policyengine_us/tests/policy/baseline/gov/states/ca/cdss/state_supplement/ca_state_supplement.yaml
+++ b/policyengine_us/tests/policy/baseline/gov/states/ca/cdss/state_supplement/ca_state_supplement.yaml
@@ -833,3 +833,115 @@
     # 1,233.94 - 0 - (800.0833 - 20) = 453.8567, which rounds up to 453.86
     # (POMS SI 02001.010 A.2).
     ca_state_supplement_person: [453.86, 0]
+
+- name: California counts January's SSI in-kind support for the SSI member of a split SSI and CAPI couple.
+  period: 2024-01
+  absolute_error_margin: 0.01
+  input:
+    people:
+      citizen:
+        age:
+          2024: 72
+        immigration_status:
+          2024: CITIZEN
+        ssi_receives_food_from_others:
+          2024: true
+      noncitizen:
+        age:
+          2024: 68
+        immigration_status:
+          2024: LEGAL_PERMANENT_RESIDENT
+        ssi_qualifying_quarters_earnings:
+          2024: 39
+    marital_units:
+      couple:
+        members: [citizen, noncitizen]
+    households:
+      household:
+        members: [citizen, noncitizen]
+        state_code:
+          2024: CA
+        living_arrangements_allow_for_food_preparation:
+          2024: true
+  output:
+    ca_capi_eligible_person: [false, true]
+    # Couple PMV = 1,415 / 3 + 20 = 491.666667 for the recipient.
+    ssi_in_kind_support_and_maintenance: [491.666667, 0]
+    # SSI = 1,415 / 2 - (491.666667 - 20) / 2 = 471.666667.
+    ssi: [471.666667, 0]
+    # Own income = 491.666667 - 20 = 471.666667.
+    # SSP = ceil_cent(1,182.94 - 471.666667 - 471.666667) = 239.61.
+    ca_state_supplement_person: [239.61, 0]
+
+- name: California counts November's SSI in-kind support in the split couple's November supplement.
+  period: 2024-11
+  absolute_error_margin: 0.01
+  input:
+    people:
+      citizen:
+        age:
+          2024: 72
+        immigration_status:
+          2024: CITIZEN
+        ssi_receives_food_from_others:
+          2024: true
+      noncitizen:
+        age:
+          2024: 68
+        immigration_status:
+          2024: LEGAL_PERMANENT_RESIDENT
+        ssi_qualifying_quarters_earnings:
+          2024: 39
+    marital_units:
+      couple:
+        members: [citizen, noncitizen]
+    households:
+      household:
+        members: [citizen, noncitizen]
+        state_code:
+          2024: CA
+        living_arrangements_allow_for_food_preparation:
+          2024: true
+  output:
+    ca_capi_eligible_person: [false, true]
+    # November uses September food; the January arithmetic still applies.
+    ssi_in_kind_support_and_maintenance: [491.666667, 0]
+    ssi: [471.666667, 0]
+    ca_state_supplement_person: [239.61, 0]
+
+- name: California counts no SSI in-kind support in the split couple's December 2024 supplement.
+  period: 2024-12
+  absolute_error_margin: 0.01
+  input:
+    people:
+      citizen:
+        age:
+          2024: 72
+        immigration_status:
+          2024: CITIZEN
+        ssi_receives_food_from_others:
+          2024: true
+      noncitizen:
+        age:
+          2024: 68
+        immigration_status:
+          2024: LEGAL_PERMANENT_RESIDENT
+        ssi_qualifying_quarters_earnings:
+          2024: 39
+    marital_units:
+      couple:
+        members: [citizen, noncitizen]
+    households:
+      household:
+        members: [citizen, noncitizen]
+        state_code:
+          2024: CA
+        living_arrangements_allow_for_food_preparation:
+          2024: true
+  output:
+    ca_capi_eligible_person: [false, true]
+    # October food no longer counts; SSI = 1,415 / 2 = 707.50.
+    ssi_in_kind_support_and_maintenance: [0, 0]
+    ssi: [707.50, 0]
+    # SSP = 1,182.94 - 707.50 - 0 = 475.44.
+    ca_state_supplement_person: [475.44, 0]
diff --git a/policyengine_us/tests/policy/baseline/gov/states/md/dhs/fia/paa/md_paa_countable_income.yaml b/policyengine_us/tests/policy/baseline/gov/states/md/dhs/fia/paa/md_paa_countable_income.yaml
index cd9a5f71e76..9cd1f185d58 100644
--- a/policyengine_us/tests/policy/baseline/gov/states/md/dhs/fia/paa/md_paa_countable_income.yaml
+++ b/policyengine_us/tests/policy/baseline/gov/states/md/dhs/fia/paa/md_paa_countable_income.yaml
@@ -46,7 +46,7 @@
     ssi_countable_income: 0
     md_paa_countable_income: 2_480
 
-- name: Case 4, a spouse's facility stay from July counts by December's status for the whole year, as an annual approximation.
+- name: Case 4, a spouse's facility stay from July separates the couple's income from July.
   period: 2025
   absolute_error_margin: 0.01
   input:
@@ -79,16 +79,161 @@
     ssi_couple_computation_applies:
       2025-06: [true, true]
       2025-07: [false, false]
-    # This annual formula applies December's status, separate, to the whole
-    # year, so each spouse counts their own income in all twelve months,
-    # including January to June, when SSI combines the couple's income.
-    # person1: (1,000 - 20) + (1,000 - 65) / 2 = 980 + 467.50 = 1,447.50,
-    # x 12 = 17,370. person2: (500 - 20) x 12 = 5,760.
+    # January to June each spouse counts half of the couple's combined income
+    # (20 CFR 416.1802(b)(1)): earned 1,000 and unearned 1,000 + 500 = 1,500 a
+    # month, so (1,500 - 20) + (1,000 - 65) / 2 = 1,480 + 467.50 = 1,947.50,
+    # and 1,947.50 / 2 = 973.75 each.
+    # July to December each spouse counts their own income (20 CFR
+    # 416.414(b)(3)): person1 (1,000 - 20) + (1,000 - 65) / 2 = 1,447.50;
+    # person2 500 - 20 = 480.
     # Both spouses are aged, so neither is an ineligible spouse and no
     # income is deemed.
-    # Summing the monthly ssi_marital_* variables instead would combine the
-    # couple's income through June. Unearned, 1,500 a month: person1
-    # 15,000 - 240 + 5,610 = 20,370 and person2 12,000 - 240 = 11,760.
-    # Earned, 1,000 a month: person2 gets 6,000 a year, so
-    # 5,760 + (500 - 65) / 2 x 12 = 8,370.
-    md_paa_countable_income: [17_370, 5_760]
+    # Year: person1 6 x 973.75 + 6 x 1,447.50 = 5,842.50 + 8,685 = 14,527.50;
+    # person2 6 x 973.75 + 6 x 480 = 5,842.50 + 2,880 = 8,722.50. The two sum
+    # to 23,250 = 6 x 1,947.50 + 6 x (1,447.50 + 480), the couple's income
+    # net of exclusions.
+    md_paa_countable_income:
+      2025-06: [973.75, 973.75]
+      2025-07: [1_447.50, 480]
+      2025: [14_527.50, 8_722.50]
+
+- name: Maryland counts January's SSI in-kind support in January PAA income.
+  period: 2024-01
+  absolute_error_margin: 0.01
+  input:
+    people:
+      person:
+        age:
+          2024: 70
+        ssi_receives_food_from_others:
+          2024: true
+        md_paa_living_arrangement:
+          2024: CARE_HOME_LEVEL_C
+    households:
+      household:
+        members: [person]
+        state_code:
+          2024: MD
+  output:
+    # ISM = 943 / 3 + 20; countable = ISM - 20 = 314.333333.
+    ssi_in_kind_support_and_maintenance: 334.333333
+    md_paa_countable_income: 314.333333
+    # Imputed SSI = 943 - 314.333333 = 628.666667.
+    md_paa_imputed_federal_ssi: 628.666667
+    # PAA = 1,173 + 98 - 314.333333 - 628.666667 = 328.
+    md_paa: 328
+
+- name: Maryland counts November's SSI in-kind support in November PAA income.
+  period: 2024-11
+  absolute_error_margin: 0.01
+  input:
+    people:
+      person:
+        age:
+          2024: 70
+        ssi_receives_food_from_others:
+          2024: true
+        md_paa_living_arrangement:
+          2024: CARE_HOME_LEVEL_C
+    households:
+      household:
+        members: [person]
+        state_code:
+          2024: MD
+  output:
+    # November retains food ISM from September under SSI's payment timing.
+    ssi_in_kind_support_and_maintenance: 334.333333
+    md_paa_countable_income: 314.333333
+    md_paa_imputed_federal_ssi: 628.666667
+    # PAA = 1,173 + 102 - 943 = 332 after the July PNA increase.
+    md_paa: 332
+
+- name: Maryland counts no SSI in-kind support in December 2024 PAA income.
+  period: 2024-12
+  absolute_error_margin: 0.01
+  input:
+    people:
+      person:
+        age:
+          2024: 70
+        ssi_receives_food_from_others:
+          2024: true
+        md_paa_living_arrangement:
+          2024: CARE_HOME_LEVEL_C
+    households:
+      household:
+        members: [person]
+        state_code:
+          2024: MD
+  output:
+    # October food no longer counts, so December ISM and countable income = 0.
+    ssi_in_kind_support_and_maintenance: 0
+    md_paa_countable_income: 0
+    md_paa_imputed_federal_ssi: 943
+    # PAA = 1,173 + 102 - 0 - 943 = 332.
+    md_paa: 332
+
+- name: Maryland sums monthly countable income without carrying December's unused exclusion.
+  period: 2024
+  absolute_error_margin: 0.01
+  input:
+    age: 70
+    state_code: MD
+    ssi_receives_food_from_others: true
+  output:
+    # 11 * (943 / 3 + 20) = 3,677.666667 gross ISM.
+    ssi_in_kind_support_and_maintenance: 3_677.666667
+    # 11 * (943 / 3) + 0 = 3,457.666667 countable income.
+    md_paa_countable_income: 3_457.666667
+
+- name: Maryland adds the month's income deemed from an ineligible spouse to that month's PAA income.
+  period: 2026
+  absolute_error_margin: 0.01
+  input:
+    people:
+      claimant:
+        age: 70
+        ssi_receives_outside_shelter_support:
+          2026-01: false
+          2026-07: true
+          2026-08: false
+      spouse:
+        age: 60
+        employment_income: 24_000
+    tax_units:
+      couple:
+        members: [claimant, spouse]
+    marital_units:
+      couple:
+        members: [claimant, spouse]
+    households:
+      home:
+        members: [claimant, spouse]
+        state_code: MD
+  output:
+    # The spouse's $2,000 of monthly wages exceeds 1,491 - 994 = 497, so SSA
+    # combines the spouses' incomes (20 CFR 416.1163(d)(2)). The claimant
+    # receives shelter support in July alone, at the presumed maximum value
+    # of 1,491 / 6 + 10 = 258.50 (POMS SI 01320.150 B.1.a).
+    # https://secure.ssa.gov/poms.nsf/lnx/0501320150
+    # The deemed income is the couple's countable income less the
+    # claimant's own.
+    # January: the couple counts (2,000 - 20 - 65) / 2 = 957.50 and the
+    # claimant alone counts 0, which leaves 957.50.
+    # July: the couple counts (258.50 - 20) + (2,000 - 65) / 2 = 238.50 +
+    # 967.50 = 1,206 and the claimant alone counts 258.50 - 20 = 238.50,
+    # which leaves 967.50.
+    ssi_income_deemed_from_ineligible_spouse_monthly:
+      2026-01: [957.50, 0]
+      2026-07: [967.50, 0]
+    # The claimant counts own income plus that month's deemed income:
+    # 0 + 957.50 = 957.50 in January and 238.50 + 967.50 = 1,206 in July.
+    # One-twelfth of the year's deemed income, (11 x 957.50 + 967.50) / 12 =
+    # 958.33, would give 958.33 in January and 1,196.83 in July.
+    # The spouse counts own wages: (2,000 - 20 - 65) / 2 = 957.50 a month.
+    # Year: claimant 11 x 957.50 + 1,206 = 11,738.50; spouse 12 x 957.50 =
+    # 11,490.
+    md_paa_countable_income:
+      2026-01: [957.50, 957.50]
+      2026-07: [1_206, 957.50]
+      2026: [11_738.50, 11_490]
diff --git a/policyengine_us/variables/gov/states/ca/cdss/state_supplement/ca_state_supplement_person.py b/policyengine_us/variables/gov/states/ca/cdss/state_supplement/ca_state_supplement_person.py
index f4aaf8ae212..5e4cf980210 100644
--- a/policyengine_us/variables/gov/states/ca/cdss/state_supplement/ca_state_supplement_person.py
+++ b/policyengine_us/variables/gov/states/ca/cdss/state_supplement/ca_state_supplement_person.py
@@ -4,7 +4,7 @@
     ssi_state_supplement,
 )
 from policyengine_us.variables.gov.ssa.ssi.eligibility.income._apply_ssi_exclusions import (
-    _apply_ssi_exclusions,
+    _apply_ssi_exclusions_monthly,
 )
 from policyengine_us.variables.gov.ssa.ssi.eligibility.resources.deemed._ssi_spouses import (
     _ssi_couple_total,
@@ -89,12 +89,12 @@ def formula(person, period, parameters):
         )
         # NOTE: in-kind support uses the couple's presumed maximum value here,
         # because SSI still treats the pair as a couple.
-        unearned = person("ssi_unearned_income", period.this_year) + person(
-            "ssi_in_kind_support_and_maintenance", period.this_year
+        ism = person("ssi_in_kind_support_and_maintenance", period)
+        unearned = (
+            person("ssi_unearned_income", period.this_year) / MONTHS_IN_YEAR + ism
         )
-        # _apply_ssi_exclusions takes and returns annual amounts.
-        own_countable_income = (
-            _apply_ssi_exclusions(earned, unearned, parameters, period) / MONTHS_IN_YEAR
+        own_countable_income = _apply_ssi_exclusions_monthly(
+            earned / MONTHS_IN_YEAR, unearned, parameters, period
         )
         ssi_countable_income = person("ssi_countable_income", period)
         couple_income = _ssi_couple_total(
diff --git a/policyengine_us/variables/gov/states/md/dhs/fia/paa/md_paa_countable_income.py b/policyengine_us/variables/gov/states/md/dhs/fia/paa/md_paa_countable_income.py
index d5760a1b635..1cec1b9fe3f 100644
--- a/policyengine_us/variables/gov/states/md/dhs/fia/paa/md_paa_countable_income.py
+++ b/policyengine_us/variables/gov/states/md/dhs/fia/paa/md_paa_countable_income.py
@@ -1,6 +1,6 @@
 from policyengine_us.model_api import *
 from policyengine_us.variables.gov.ssa.ssi.eligibility.income._apply_ssi_exclusions import (
-    _apply_ssi_exclusions,
+    _apply_ssi_exclusions_monthly,
 )
 from policyengine_us.variables.gov.ssa.ssi.eligibility.resources.deemed._ssi_spouses import (
     _ssi_couple_income,
@@ -12,7 +12,7 @@ class md_paa_countable_income(Variable):
     entity = Person
     label = "Maryland PAA countable income"
     unit = USD
-    definition_period = YEAR
+    definition_period = MONTH
     defined_for = StateCode.MD
     reference = (
         "https://regs.maryland.gov/us/md/exec/comar/07.03.07.07",
@@ -26,12 +26,9 @@ def formula(person, period, parameters):
         # exclusions, but it must count income for every PAA eligibility
         # pathway. Using ssi_countable_income would zero out SSDI-only
         # recipients unless an input also marks them as SSI-disabled.
-        # NOTE: this annual formula applies one couple status to the whole
-        # year (both_eligible below), so it combines the spouses' annual
-        # income by that same status. ssi_marital_earned_income and
-        # ssi_marital_unearned_income are monthly and follow each month's
-        # status; their annual totals would not match it in a year with a
-        # part-year facility stay.
+        # _ssi_couple_income and both_eligible read the same month's couple
+        # status, so a month in which one spouse stays in a medical facility
+        # counts each spouse's own income (20 CFR 416.414(b)(3)).
         earned = _ssi_couple_income(person, period, "ssi_earned_income")
         student_exclusion = person(
             "ssi_blind_or_disabled_working_student_exclusion", period
@@ -42,14 +39,14 @@ def formula(person, period, parameters):
             + person("ssi_unearned_income_deemed_from_ineligible_parent", period)
             + person("ssi_in_kind_support_and_maintenance", period)
         )
-        personal_countable = _apply_ssi_exclusions(
+        personal_countable = _apply_ssi_exclusions_monthly(
             adjusted_earned,
             unearned,
             parameters,
             period,
         )
 
-        both_eligible = person("ssi_couple_computation_applies", period.this_year)
+        both_eligible = person("ssi_couple_computation_applies", period)
         # COMAR 07.03.07.07 counts the individual's own income and has no
         # spousal deeming, so people who fail SSI's citizen or
         # qualified-noncitizen test count their own income alone, including
@@ -61,9 +58,12 @@ def formula(person, period, parameters):
         is_citizen = immigration_status == immigration_status.possible_values.CITIZEN
         is_qualified_noncitizen = person("is_ssi_qualified_noncitizen", period)
         meets_ssi_immigration_test = is_citizen | is_qualified_noncitizen
+        # The deemed amount comes from the same month as the income above:
+        # ssi_income_deemed_from_ineligible_spouse_monthly counts that month's
+        # in-kind support in the couple's budget and in the claimant's.
         spousal_deemed = where(
             meets_ssi_immigration_test,
-            person("ssi_income_deemed_from_ineligible_spouse", period),
+            person("ssi_income_deemed_from_ineligible_spouse_monthly", period),
             0,
         )
         return where(