diff --git a/changelog.d/il-hbwd-premium-band-edges.fixed.md b/changelog.d/il-hbwd-premium-band-edges.fixed.md
new file mode 100644
index 00000000000..1102a687b4b
--- /dev/null
+++ b/changelog.d/il-hbwd-premium-band-edges.fixed.md
@@ -0,0 +1 @@
+Key the Illinois Health Benefits for Workers with Disabilities premium bands at the chart's band starts, so income of exactly $250, $500 and so on pays the lower band's premium.
diff --git a/policyengine_us/parameters/gov/states/il/hfs/hbwd/premium/earned.yaml b/policyengine_us/parameters/gov/states/il/hfs/hbwd/premium/earned.yaml
index 0d71a038a63..8ceb71a31d4 100644
--- a/policyengine_us/parameters/gov/states/il/hfs/hbwd/premium/earned.yaml
+++ b/policyengine_us/parameters/gov/states/il/hfs/hbwd/premium/earned.yaml
@@ -6,91 +6,98 @@ metadata:
   period: month
   label: Illinois HBWD earned income premium component
   reference:
-    # Illinois presents the table as a matrix, but the values can be summed between row 1 and column 1.
-    - title: 89 Ill. Admin. Code § 120.510 (n)
+    # Summing the first column (earned) and first row (unearned) reproduces 434 of the 441
+    # cells in 120.510(n)(3); see issue 10471 for the others.
+    # Thresholds are the chart's band starts (0-250, 251-500, ..., 4751-5000, 5000+), so income of
+    # exactly $250 stays in the first band; $5,000 falls in the 4751-5000 band.
+    # Bands start at whole dollars, so income with cents stays in the band of its whole-dollar
+    # amount, as IDHS PM 15-04-03 drops cents.
+    - title: 89 Ill. Admin. Code § 120.510(n)(3)
       href: https://www.law.cornell.edu/regulations/illinois/Ill-Admin-Code-tit-89-SS-120.510
+    - title: Illinois HFS, Health Benefits for Workers with Disabilities Premium Chart
+      href: https://hfs.illinois.gov/content/dam/soi/en/web/hfs/medicalprograms/hbwd/documents/hfsweb004.pdf
 brackets:
   - threshold:
       2022-04-01: 0
     amount:
       2022-04-01: 0
   - threshold:
-      2022-04-01: 250
+      2022-04-01: 251
     amount:
       2022-04-01: 6
   - threshold:
-      2022-04-01: 500
+      2022-04-01: 501
     amount:
       2022-04-01: 13
   - threshold:
-      2022-04-01: 750
+      2022-04-01: 751
     amount:
       2022-04-01: 19
   - threshold:
-      2022-04-01: 1_000
+      2022-04-01: 1_001
     amount:
       2022-04-01: 25
   - threshold:
-      2022-04-01: 1_250
+      2022-04-01: 1_251
     amount:
       2022-04-01: 31
   - threshold:
-      2022-04-01: 1_500
+      2022-04-01: 1_501
     amount:
       2022-04-01: 38
   - threshold:
-      2022-04-01: 1_750
+      2022-04-01: 1_751
     amount:
       2022-04-01: 44
   - threshold:
-      2022-04-01: 2_000
+      2022-04-01: 2_001
     amount:
       2022-04-01: 50
   - threshold:
-      2022-04-01: 2_250
+      2022-04-01: 2_251
     amount:
       2022-04-01: 56
   - threshold:
-      2022-04-01: 2_500
+      2022-04-01: 2_501
     amount:
       2022-04-01: 63
   - threshold:
-      2022-04-01: 2_750
+      2022-04-01: 2_751
     amount:
       2022-04-01: 69
   - threshold:
-      2022-04-01: 3_000
+      2022-04-01: 3_001
     amount:
       2022-04-01: 75
   - threshold:
-      2022-04-01: 3_250
+      2022-04-01: 3_251
     amount:
       2022-04-01: 81
   - threshold:
-      2022-04-01: 3_500
+      2022-04-01: 3_501
     amount:
       2022-04-01: 88
   - threshold:
-      2022-04-01: 3_750
+      2022-04-01: 3_751
     amount:
       2022-04-01: 94
   - threshold:
-      2022-04-01: 4_000
+      2022-04-01: 4_001
     amount:
       2022-04-01: 100
   - threshold:
-      2022-04-01: 4_250
+      2022-04-01: 4_251
     amount:
       2022-04-01: 106
   - threshold:
-      2022-04-01: 4_500
+      2022-04-01: 4_501
     amount:
       2022-04-01: 113
   - threshold:
-      2022-04-01: 4_750
+      2022-04-01: 4_751
     amount:
       2022-04-01: 119
   - threshold:
-      2022-04-01: 5_000
+      2022-04-01: 5_001
     amount:
       2022-04-01: 125
diff --git a/policyengine_us/parameters/gov/states/il/hfs/hbwd/premium/unearned.yaml b/policyengine_us/parameters/gov/states/il/hfs/hbwd/premium/unearned.yaml
index e62138f1811..ce20aaa5162 100644
--- a/policyengine_us/parameters/gov/states/il/hfs/hbwd/premium/unearned.yaml
+++ b/policyengine_us/parameters/gov/states/il/hfs/hbwd/premium/unearned.yaml
@@ -6,91 +6,98 @@ metadata:
   period: month
   label: Illinois HBWD unearned income premium component
   reference:
-    # Illinois presents the table as a matrix, but the values can be summed between row 1 and column 1.
-    - title: 89 Ill. Admin. Code § 120.510 (n)
+    # Summing the first column (earned) and first row (unearned) reproduces 434 of the 441
+    # cells in 120.510(n)(3); see issue 10471 for the others.
+    # Thresholds are the chart's band starts (0-250, 251-500, ..., 4751-5000, 5000+), so income of
+    # exactly $250 stays in the first band; $5,000 falls in the 4751-5000 band.
+    # Bands start at whole dollars, so income with cents stays in the band of its whole-dollar
+    # amount, as IDHS PM 15-04-03 drops cents.
+    - title: 89 Ill. Admin. Code § 120.510(n)(3)
       href: https://www.law.cornell.edu/regulations/illinois/Ill-Admin-Code-tit-89-SS-120.510
+    - title: Illinois HFS, Health Benefits for Workers with Disabilities Premium Chart
+      href: https://hfs.illinois.gov/content/dam/soi/en/web/hfs/medicalprograms/hbwd/documents/hfsweb004.pdf
 brackets:
   - threshold:
       2022-04-01: 0
     amount:
       2022-04-01: 0
   - threshold:
-      2022-04-01: 250
+      2022-04-01: 251
     amount:
       2022-04-01: 19
   - threshold:
-      2022-04-01: 500
+      2022-04-01: 501
     amount:
       2022-04-01: 38
   - threshold:
-      2022-04-01: 750
+      2022-04-01: 751
     amount:
       2022-04-01: 56
   - threshold:
-      2022-04-01: 1_000
+      2022-04-01: 1_001
     amount:
       2022-04-01: 75
   - threshold:
-      2022-04-01: 1_250
+      2022-04-01: 1_251
     amount:
       2022-04-01: 94
   - threshold:
-      2022-04-01: 1_500
+      2022-04-01: 1_501
     amount:
       2022-04-01: 113
   - threshold:
-      2022-04-01: 1_750
+      2022-04-01: 1_751
     amount:
       2022-04-01: 131
   - threshold:
-      2022-04-01: 2_000
+      2022-04-01: 2_001
     amount:
       2022-04-01: 150
   - threshold:
-      2022-04-01: 2_250
+      2022-04-01: 2_251
     amount:
       2022-04-01: 169
   - threshold:
-      2022-04-01: 2_500
+      2022-04-01: 2_501
     amount:
       2022-04-01: 188
   - threshold:
-      2022-04-01: 2_750
+      2022-04-01: 2_751
     amount:
       2022-04-01: 206
   - threshold:
-      2022-04-01: 3_000
+      2022-04-01: 3_001
     amount:
       2022-04-01: 225
   - threshold:
-      2022-04-01: 3_250
+      2022-04-01: 3_251
     amount:
       2022-04-01: 244
   - threshold:
-      2022-04-01: 3_500
+      2022-04-01: 3_501
     amount:
       2022-04-01: 263
   - threshold:
-      2022-04-01: 3_750
+      2022-04-01: 3_751
     amount:
       2022-04-01: 281
   - threshold:
-      2022-04-01: 4_000
+      2022-04-01: 4_001
     amount:
       2022-04-01: 300
   - threshold:
-      2022-04-01: 4_250
+      2022-04-01: 4_251
     amount:
       2022-04-01: 319
   - threshold:
-      2022-04-01: 4_500
+      2022-04-01: 4_501
     amount:
       2022-04-01: 338
   - threshold:
-      2022-04-01: 4_750
+      2022-04-01: 4_751
     amount:
       2022-04-01: 356
   - threshold:
-      2022-04-01: 5_000
+      2022-04-01: 5_001
     amount:
       2022-04-01: 375
diff --git a/policyengine_us/tests/policy/baseline/gov/states/il/hfs/hbwd/il_hbwd_person.yaml b/policyengine_us/tests/policy/baseline/gov/states/il/hfs/hbwd/il_hbwd_person.yaml
index 19124990d6f..2c4185062ae 100644
--- a/policyengine_us/tests/policy/baseline/gov/states/il/hfs/hbwd/il_hbwd_person.yaml
+++ b/policyengine_us/tests/policy/baseline/gov/states/il/hfs/hbwd/il_hbwd_person.yaml
@@ -7,11 +7,11 @@
     il_hbwd_countable_earned_income: 1_000
     il_hbwd_countable_unearned_income: 1_200
   output:
-    il_hbwd_person: -100
-    # Premium: $100 (earned $25 + unearned $75)
-    # Earned $1,000 → bracket 4 → $25
-    # Unearned $1,200 → bracket 4 → $75
-    # Benefit: -$100 (cost to individual)
+    il_hbwd_person: -94
+    # Premium: $94 (earned $19 + unearned $75)
+    # Earned $1,000 → 751-1000 band → $19
+    # Unearned $1,200 → 1001-1250 band → $75
+    # Benefit: -$94 (cost to individual)
 
 - name: Case 2, HBWD person not eligible.
   period: 2024-01
@@ -31,4 +31,4 @@
     il_hbwd_countable_unearned_income: 0
   output:
     il_hbwd_person: 0
-    # Both income in first bracket → $0 premium
+    # Both incomes in the 0-250 band → $0 premium
diff --git a/policyengine_us/tests/policy/baseline/gov/states/il/hfs/hbwd/il_hbwd_premium.yaml b/policyengine_us/tests/policy/baseline/gov/states/il/hfs/hbwd/il_hbwd_premium.yaml
index a45e67f3de7..529eac111de 100644
--- a/policyengine_us/tests/policy/baseline/gov/states/il/hfs/hbwd/il_hbwd_premium.yaml
+++ b/policyengine_us/tests/policy/baseline/gov/states/il/hfs/hbwd/il_hbwd_premium.yaml
@@ -7,10 +7,10 @@
     il_hbwd_countable_earned_income: 2_000
     il_hbwd_countable_unearned_income: 0
   output:
-    il_hbwd_premium: 50
-    # Earned $2,000 → bracket 8 (2001-2250) → $50
-    # Unearned $0 → bracket 0 → $0
-    # Total: $50
+    il_hbwd_premium: 44
+    # Earned $2,000 → 1751-2000 band → $44
+    # Unearned $0 → 0-250 band → $0
+    # Total: $44
 
 - name: Case 2, premium with earned and unearned.
   period: 2024-01
@@ -21,10 +21,10 @@
     il_hbwd_countable_earned_income: 1_000
     il_hbwd_countable_unearned_income: 1_200
   output:
-    il_hbwd_premium: 100
-    # Earned $1,000 → bracket 4 (1001-1250) → $25
-    # Unearned $1,200 → bracket 4 (1001-1250) → $75
-    # Total: $25 + $75 = $100
+    il_hbwd_premium: 94
+    # Earned $1,000 → 751-1000 band → $19
+    # Unearned $1,200 → 1001-1250 band → $75
+    # Total: $19 + $75 = $94
 
 - name: Case 3, premium with higher income.
   period: 2024-01
@@ -35,27 +35,26 @@
     il_hbwd_countable_earned_income: 3_000
     il_hbwd_countable_unearned_income: 2_000
   output:
-    il_hbwd_premium: 225
-    # Earned $3,000 → bracket 12 (3001-3250) → $75
-    # Unearned $2,000 → bracket 8 (2001-2250) → $150
-    # Total: $75 + $150 = $225
+    il_hbwd_premium: 200
+    # Earned $3,000 → 2751-3000 band → $69
+    # Unearned $2,000 → 1751-2000 band → $131
+    # Total: $69 + $131 = $200
 
-- name: Case 4, premium capped at $500.
+- name: Case 4, income above $5,000 of each type pays the chart's highest premium.
   period: 2024-01
   absolute_error_margin: 0.01
   input:
     state_code: IL
     il_hbwd_eligible: true
-    il_hbwd_countable_earned_income: 5_000
-    il_hbwd_countable_unearned_income: 5_000
+    il_hbwd_countable_earned_income: 5_001
+    il_hbwd_countable_unearned_income: 5_001
   output:
     il_hbwd_premium: 500
-    # Earned $5,000+ → bracket 20 → $125
-    # Unearned $5,000+ → bracket 20 → $375
-    # Uncapped: $500
-    # Capped: $500
+    # Earned above $5,000 → 5000+ band → $125
+    # Unearned above $5,000 → 5000+ band → $375
+    # Total: $500, the chart's highest premium
 
-- name: Case 5, no premium in first bracket.
+- name: Case 5, no premium in the 0-250 band.
   period: 2024-01
   absolute_error_margin: 0.01
   input:
@@ -65,11 +64,11 @@
     il_hbwd_countable_unearned_income: 0
   output:
     il_hbwd_premium: 0
-    # Earned $200 → bracket 0 (0-250) → $0
-    # Unearned $0 → bracket 0 → $0
+    # Earned $200 → 0-250 band → $0
+    # Unearned $0 → 0-250 band → $0
     # Total: $0
 
-- name: Case 6, verify bracket boundary at $250.
+- name: Case 6, income of exactly $250 is in the 0-250 band.
   period: 2024-01
   absolute_error_margin: 0.01
   input:
@@ -78,10 +77,10 @@
     il_hbwd_countable_earned_income: 250
     il_hbwd_countable_unearned_income: 250
   output:
-    il_hbwd_premium: 25
-    # Earned $250 → bracket 1 (251-500) → $6
-    # Unearned $250 → bracket 1 (251-500) → $19
-    # Total: $6 + $19 = $25
+    il_hbwd_premium: 0
+    # Earned $250 → 0-250 band → $0
+    # Unearned $250 → 0-250 band → $0
+    # Total: $0
 
 - name: Case 7, married couple both disabled, each premium uses only their own withholding.
   period: 2025-01
@@ -116,6 +115,188 @@
     il_hbwd_countable_earned_income: [1_802.61, 1_802.61]
     il_hbwd_countable_unearned_income: [0, 0]
     il_hbwd_premium: [44, 44]
-    # Earned $1,802.61 → bracket 7 (1751-2000) → $44
-    # Unearned $0 → bracket 0 → $0
+    # Earned $1,802.61 → 1751-2000 band → $44
+    # Unearned $0 → 0-250 band → $0
     # Deducting the couple's combined withholding would give 1,710.41 → $38
+
+- name: Case 8, income of exactly $5,000 is in the 4751-5000 band, not the 5000+ band.
+  period: 2026-01
+  absolute_error_margin: 0.01
+  input:
+    state_code: IL
+    il_hbwd_eligible: true
+    il_hbwd_countable_earned_income: 5_000
+    il_hbwd_countable_unearned_income: 5_000
+  output:
+    il_hbwd_premium: 475
+    # Earned $5,000 → 4751-5000 band → $119
+    # Unearned $5,000 → 4751-5000 band → $356
+    # Total: $119 + $356 = $475
+
+- name: Case 9, earned income at each band start (251, 501, ..., 5,001) pays that band's premium.
+  period: 2026-01
+  absolute_error_margin: 0.01
+  input:
+    people:
+      person1: {il_hbwd_eligible: true, il_hbwd_countable_earned_income: 251, il_hbwd_countable_unearned_income: 0}
+      person2: {il_hbwd_eligible: true, il_hbwd_countable_earned_income: 501, il_hbwd_countable_unearned_income: 0}
+      person3: {il_hbwd_eligible: true, il_hbwd_countable_earned_income: 751, il_hbwd_countable_unearned_income: 0}
+      person4: {il_hbwd_eligible: true, il_hbwd_countable_earned_income: 1_001, il_hbwd_countable_unearned_income: 0}
+      person5: {il_hbwd_eligible: true, il_hbwd_countable_earned_income: 1_251, il_hbwd_countable_unearned_income: 0}
+      person6: {il_hbwd_eligible: true, il_hbwd_countable_earned_income: 1_501, il_hbwd_countable_unearned_income: 0}
+      person7: {il_hbwd_eligible: true, il_hbwd_countable_earned_income: 1_751, il_hbwd_countable_unearned_income: 0}
+      person8: {il_hbwd_eligible: true, il_hbwd_countable_earned_income: 2_001, il_hbwd_countable_unearned_income: 0}
+      person9: {il_hbwd_eligible: true, il_hbwd_countable_earned_income: 2_251, il_hbwd_countable_unearned_income: 0}
+      person10: {il_hbwd_eligible: true, il_hbwd_countable_earned_income: 2_501, il_hbwd_countable_unearned_income: 0}
+      person11: {il_hbwd_eligible: true, il_hbwd_countable_earned_income: 2_751, il_hbwd_countable_unearned_income: 0}
+      person12: {il_hbwd_eligible: true, il_hbwd_countable_earned_income: 3_001, il_hbwd_countable_unearned_income: 0}
+      person13: {il_hbwd_eligible: true, il_hbwd_countable_earned_income: 3_251, il_hbwd_countable_unearned_income: 0}
+      person14: {il_hbwd_eligible: true, il_hbwd_countable_earned_income: 3_501, il_hbwd_countable_unearned_income: 0}
+      person15: {il_hbwd_eligible: true, il_hbwd_countable_earned_income: 3_751, il_hbwd_countable_unearned_income: 0}
+      person16: {il_hbwd_eligible: true, il_hbwd_countable_earned_income: 4_001, il_hbwd_countable_unearned_income: 0}
+      person17: {il_hbwd_eligible: true, il_hbwd_countable_earned_income: 4_251, il_hbwd_countable_unearned_income: 0}
+      person18: {il_hbwd_eligible: true, il_hbwd_countable_earned_income: 4_501, il_hbwd_countable_unearned_income: 0}
+      person19: {il_hbwd_eligible: true, il_hbwd_countable_earned_income: 4_751, il_hbwd_countable_unearned_income: 0}
+      person20: {il_hbwd_eligible: true, il_hbwd_countable_earned_income: 5_001, il_hbwd_countable_unearned_income: 0}
+    households:
+      household:
+        members: [person1, person2, person3, person4, person5, person6, person7, person8, person9, person10,
+          person11, person12, person13, person14, person15, person16, person17, person18, person19, person20]
+        state_code: IL
+  output:
+    il_hbwd_premium: [6, 13, 19, 25, 31, 38, 44, 50, 56, 63, 69, 75, 81, 88, 94, 100, 106, 113, 119, 125]
+    # First column of the chart, bands 251-500 through 5000+.
+
+- name: Case 10, earned income one dollar below each band start (250, 500, ..., 5,000) pays the lower band's premium.
+  period: 2026-01
+  absolute_error_margin: 0.01
+  input:
+    people:
+      person1: {il_hbwd_eligible: true, il_hbwd_countable_earned_income: 250, il_hbwd_countable_unearned_income: 0}
+      person2: {il_hbwd_eligible: true, il_hbwd_countable_earned_income: 500, il_hbwd_countable_unearned_income: 0}
+      person3: {il_hbwd_eligible: true, il_hbwd_countable_earned_income: 750, il_hbwd_countable_unearned_income: 0}
+      person4: {il_hbwd_eligible: true, il_hbwd_countable_earned_income: 1_000, il_hbwd_countable_unearned_income: 0}
+      person5: {il_hbwd_eligible: true, il_hbwd_countable_earned_income: 1_250, il_hbwd_countable_unearned_income: 0}
+      person6: {il_hbwd_eligible: true, il_hbwd_countable_earned_income: 1_500, il_hbwd_countable_unearned_income: 0}
+      person7: {il_hbwd_eligible: true, il_hbwd_countable_earned_income: 1_750, il_hbwd_countable_unearned_income: 0}
+      person8: {il_hbwd_eligible: true, il_hbwd_countable_earned_income: 2_000, il_hbwd_countable_unearned_income: 0}
+      person9: {il_hbwd_eligible: true, il_hbwd_countable_earned_income: 2_250, il_hbwd_countable_unearned_income: 0}
+      person10: {il_hbwd_eligible: true, il_hbwd_countable_earned_income: 2_500, il_hbwd_countable_unearned_income: 0}
+      person11: {il_hbwd_eligible: true, il_hbwd_countable_earned_income: 2_750, il_hbwd_countable_unearned_income: 0}
+      person12: {il_hbwd_eligible: true, il_hbwd_countable_earned_income: 3_000, il_hbwd_countable_unearned_income: 0}
+      person13: {il_hbwd_eligible: true, il_hbwd_countable_earned_income: 3_250, il_hbwd_countable_unearned_income: 0}
+      person14: {il_hbwd_eligible: true, il_hbwd_countable_earned_income: 3_500, il_hbwd_countable_unearned_income: 0}
+      person15: {il_hbwd_eligible: true, il_hbwd_countable_earned_income: 3_750, il_hbwd_countable_unearned_income: 0}
+      person16: {il_hbwd_eligible: true, il_hbwd_countable_earned_income: 4_000, il_hbwd_countable_unearned_income: 0}
+      person17: {il_hbwd_eligible: true, il_hbwd_countable_earned_income: 4_250, il_hbwd_countable_unearned_income: 0}
+      person18: {il_hbwd_eligible: true, il_hbwd_countable_earned_income: 4_500, il_hbwd_countable_unearned_income: 0}
+      person19: {il_hbwd_eligible: true, il_hbwd_countable_earned_income: 4_750, il_hbwd_countable_unearned_income: 0}
+      person20: {il_hbwd_eligible: true, il_hbwd_countable_earned_income: 5_000, il_hbwd_countable_unearned_income: 0}
+    households:
+      household:
+        members: [person1, person2, person3, person4, person5, person6, person7, person8, person9, person10,
+          person11, person12, person13, person14, person15, person16, person17, person18, person19, person20]
+        state_code: IL
+  output:
+    il_hbwd_premium: [0, 6, 13, 19, 25, 31, 38, 44, 50, 56, 63, 69, 75, 81, 88, 94, 100, 106, 113, 119]
+    # First column of the chart, bands 0-250 through 4751-5000.
+
+- name: Case 11, unearned income at each band start (251, 501, ..., 5,001) pays that band's premium.
+  period: 2026-01
+  absolute_error_margin: 0.01
+  input:
+    people:
+      person1: {il_hbwd_eligible: true, il_hbwd_countable_earned_income: 0, il_hbwd_countable_unearned_income: 251}
+      person2: {il_hbwd_eligible: true, il_hbwd_countable_earned_income: 0, il_hbwd_countable_unearned_income: 501}
+      person3: {il_hbwd_eligible: true, il_hbwd_countable_earned_income: 0, il_hbwd_countable_unearned_income: 751}
+      person4: {il_hbwd_eligible: true, il_hbwd_countable_earned_income: 0, il_hbwd_countable_unearned_income: 1_001}
+      person5: {il_hbwd_eligible: true, il_hbwd_countable_earned_income: 0, il_hbwd_countable_unearned_income: 1_251}
+      person6: {il_hbwd_eligible: true, il_hbwd_countable_earned_income: 0, il_hbwd_countable_unearned_income: 1_501}
+      person7: {il_hbwd_eligible: true, il_hbwd_countable_earned_income: 0, il_hbwd_countable_unearned_income: 1_751}
+      person8: {il_hbwd_eligible: true, il_hbwd_countable_earned_income: 0, il_hbwd_countable_unearned_income: 2_001}
+      person9: {il_hbwd_eligible: true, il_hbwd_countable_earned_income: 0, il_hbwd_countable_unearned_income: 2_251}
+      person10: {il_hbwd_eligible: true, il_hbwd_countable_earned_income: 0, il_hbwd_countable_unearned_income: 2_501}
+      person11: {il_hbwd_eligible: true, il_hbwd_countable_earned_income: 0, il_hbwd_countable_unearned_income: 2_751}
+      person12: {il_hbwd_eligible: true, il_hbwd_countable_earned_income: 0, il_hbwd_countable_unearned_income: 3_001}
+      person13: {il_hbwd_eligible: true, il_hbwd_countable_earned_income: 0, il_hbwd_countable_unearned_income: 3_251}
+      person14: {il_hbwd_eligible: true, il_hbwd_countable_earned_income: 0, il_hbwd_countable_unearned_income: 3_501}
+      person15: {il_hbwd_eligible: true, il_hbwd_countable_earned_income: 0, il_hbwd_countable_unearned_income: 3_751}
+      person16: {il_hbwd_eligible: true, il_hbwd_countable_earned_income: 0, il_hbwd_countable_unearned_income: 4_001}
+      person17: {il_hbwd_eligible: true, il_hbwd_countable_earned_income: 0, il_hbwd_countable_unearned_income: 4_251}
+      person18: {il_hbwd_eligible: true, il_hbwd_countable_earned_income: 0, il_hbwd_countable_unearned_income: 4_501}
+      person19: {il_hbwd_eligible: true, il_hbwd_countable_earned_income: 0, il_hbwd_countable_unearned_income: 4_751}
+      person20: {il_hbwd_eligible: true, il_hbwd_countable_earned_income: 0, il_hbwd_countable_unearned_income: 5_001}
+    households:
+      household:
+        members: [person1, person2, person3, person4, person5, person6, person7, person8, person9, person10,
+          person11, person12, person13, person14, person15, person16, person17, person18, person19, person20]
+        state_code: IL
+  output:
+    il_hbwd_premium: [19, 38, 56, 75, 94, 113, 131, 150, 169, 188, 206, 225, 244, 263, 281, 300, 319, 338, 356, 375]
+    # First row of the chart, bands 251-500 through 5000+.
+
+- name: Case 12, unearned income one dollar below each band start (250, 500, ..., 5,000) pays the lower band's premium.
+  period: 2026-01
+  absolute_error_margin: 0.01
+  input:
+    people:
+      person1: {il_hbwd_eligible: true, il_hbwd_countable_earned_income: 0, il_hbwd_countable_unearned_income: 250}
+      person2: {il_hbwd_eligible: true, il_hbwd_countable_earned_income: 0, il_hbwd_countable_unearned_income: 500}
+      person3: {il_hbwd_eligible: true, il_hbwd_countable_earned_income: 0, il_hbwd_countable_unearned_income: 750}
+      person4: {il_hbwd_eligible: true, il_hbwd_countable_earned_income: 0, il_hbwd_countable_unearned_income: 1_000}
+      person5: {il_hbwd_eligible: true, il_hbwd_countable_earned_income: 0, il_hbwd_countable_unearned_income: 1_250}
+      person6: {il_hbwd_eligible: true, il_hbwd_countable_earned_income: 0, il_hbwd_countable_unearned_income: 1_500}
+      person7: {il_hbwd_eligible: true, il_hbwd_countable_earned_income: 0, il_hbwd_countable_unearned_income: 1_750}
+      person8: {il_hbwd_eligible: true, il_hbwd_countable_earned_income: 0, il_hbwd_countable_unearned_income: 2_000}
+      person9: {il_hbwd_eligible: true, il_hbwd_countable_earned_income: 0, il_hbwd_countable_unearned_income: 2_250}
+      person10: {il_hbwd_eligible: true, il_hbwd_countable_earned_income: 0, il_hbwd_countable_unearned_income: 2_500}
+      person11: {il_hbwd_eligible: true, il_hbwd_countable_earned_income: 0, il_hbwd_countable_unearned_income: 2_750}
+      person12: {il_hbwd_eligible: true, il_hbwd_countable_earned_income: 0, il_hbwd_countable_unearned_income: 3_000}
+      person13: {il_hbwd_eligible: true, il_hbwd_countable_earned_income: 0, il_hbwd_countable_unearned_income: 3_250}
+      person14: {il_hbwd_eligible: true, il_hbwd_countable_earned_income: 0, il_hbwd_countable_unearned_income: 3_500}
+      person15: {il_hbwd_eligible: true, il_hbwd_countable_earned_income: 0, il_hbwd_countable_unearned_income: 3_750}
+      person16: {il_hbwd_eligible: true, il_hbwd_countable_earned_income: 0, il_hbwd_countable_unearned_income: 4_000}
+      person17: {il_hbwd_eligible: true, il_hbwd_countable_earned_income: 0, il_hbwd_countable_unearned_income: 4_250}
+      person18: {il_hbwd_eligible: true, il_hbwd_countable_earned_income: 0, il_hbwd_countable_unearned_income: 4_500}
+      person19: {il_hbwd_eligible: true, il_hbwd_countable_earned_income: 0, il_hbwd_countable_unearned_income: 4_750}
+      person20: {il_hbwd_eligible: true, il_hbwd_countable_earned_income: 0, il_hbwd_countable_unearned_income: 5_000}
+    households:
+      household:
+        members: [person1, person2, person3, person4, person5, person6, person7, person8, person9, person10,
+          person11, person12, person13, person14, person15, person16, person17, person18, person19, person20]
+        state_code: IL
+  output:
+    il_hbwd_premium: [0, 19, 38, 56, 75, 94, 113, 131, 150, 169, 188, 206, 225, 244, 263, 281, 300, 319, 338, 356]
+    # First row of the chart, bands 0-250 through 4751-5000.
+
+- name: Case 13, income with cents stays in the band of its whole-dollar amount.
+  period: 2026-01
+  absolute_error_margin: 0.01
+  input:
+    people:
+      person1: {il_hbwd_eligible: true, il_hbwd_countable_earned_income: 250.99, il_hbwd_countable_unearned_income: 0}
+      person2: {il_hbwd_eligible: true, il_hbwd_countable_earned_income: 5_000.99, il_hbwd_countable_unearned_income: 0}
+      person3: {il_hbwd_eligible: true, il_hbwd_countable_earned_income: 0, il_hbwd_countable_unearned_income: 250.99}
+      person4: {il_hbwd_eligible: true, il_hbwd_countable_earned_income: 0, il_hbwd_countable_unearned_income: 5_000.99}
+    households:
+      household:
+        members: [person1, person2, person3, person4]
+        state_code: IL
+  output:
+    il_hbwd_premium: [0, 119, 0, 356]
+    # $250.99 → 0-250 band; $5,000.99 → 4751-5000 band (IDHS PM 15-04-03 drops cents).
+
+- name: Case 14, HFS 3792 Example 1, $900 from work and $1,000 from Social Security.
+  period: 2026-01
+  absolute_error_margin: 0.01
+  input:
+    state_code: IL
+    il_hbwd_eligible: true
+    il_hbwd_countable_earned_income: 900
+    il_hbwd_countable_unearned_income: 1_000
+  output:
+    il_hbwd_premium: 75
+    # HFS 3792 (R-03-13), Example 1: the monthly premium is $75.
+    # Earned $900 → 751-1000 band → $19
+    # Unearned $1,000 → 751-1000 band → $56
+    # Total: $19 + $56 = $75
diff --git a/policyengine_us/tests/policy/baseline/gov/states/il/hfs/hbwd/integration.yaml b/policyengine_us/tests/policy/baseline/gov/states/il/hfs/hbwd/integration.yaml
index 75ddb4826f1..5ba4a5bc04f 100644
--- a/policyengine_us/tests/policy/baseline/gov/states/il/hfs/hbwd/integration.yaml
+++ b/policyengine_us/tests/policy/baseline/gov/states/il/hfs/hbwd/integration.yaml
@@ -19,14 +19,14 @@
     # Income calculation
     il_hbwd_gross_earned_income: 2_000  # 24,000 / 12
     il_hbwd_countable_income: 2_728.13
-    # Earned: $2,000 - $211.55 (expenses) - $50 (exemptions) = $1,738.45
-    # Unearned: $1,000 - $10 (remaining flat exemption)
-    # Total: ~$2,728.13
+    # Earned: $2,000 - $221.87 (withheld taxes) - $50 (exemption) = $1,728.13
+    # Unearned: $1,000 (counted gross)
+    # Total: $2,728.13
     # Premium calculation
-    il_hbwd_premium: 113
-    # Earned $1,713.45 → bracket 6 (1501-1750) → $38
-    # Unearned $1,000 → bracket 4 (1001-1250) → $75
-    # Total: $38 + $75 = $113
+    il_hbwd_premium: 94
+    # Earned $1,728.13 → 1501-1750 band → $38
+    # Unearned $1,000 → 751-1000 band → $56
+    # Total: $38 + $56 = $94
 
 - name: Case 2, couple with one eligible member.
   period: 2024-01
@@ -112,11 +112,13 @@
     il_hbwd_employment_eligible: true
     il_hbwd_eligible: true
     il_hbwd_income_eligible: true
-    # Total income after deductions: ~$4,089
+    # Countable income: $3,498.62 earned + $400 unearned = $3,898.62
     # 350% FPL for single (2024): ~$4,393
     # Just under limit → eligible
     il_hbwd_premium: 100
-    # Premium: $100
+    # Earned $3,498.62 → 3251-3500 band → $81
+    # Unearned $400 → 251-500 band → $19
+    # Total: $81 + $19 = $100
 
 - name: Case 5, eligible with high income after exemptions.
   period: 2024-01
@@ -133,7 +135,7 @@
     il_hbwd_employment_eligible: true
     il_hbwd_asset_eligible: true
     il_hbwd_income_eligible: true
-    # Countable income after expenses and exemptions: ~$4,618
+    # Countable income after expenses and exemptions: $4,378.95
     # With exemptions, now under 350% FPL limit
     il_hbwd_eligible: true
 
@@ -157,13 +159,13 @@
     # Income calculation
     il_hbwd_gross_earned_income: 1_000
     il_hbwd_countable_income: 2_349.95
-    # Earned after expenses and exemptions: ~$850
+    # Earned after expenses and exemptions: $849.95
     # Unearned: $1,500
-    # Total: ~$2,349.95
-    il_hbwd_premium: 132
-    # Earned $824.95 → bracket 3 (751-1000) → $19
-    # Unearned $1,500 → bracket 6 (1501-1750) → $113
-    # Total: $19 + $113 = $132
+    # Total: $2,349.95
+    il_hbwd_premium: 113
+    # Earned $849.95 → 751-1000 band → $19
+    # Unearned $1,500 → 1251-1500 band → $94
+    # Total: $19 + $94 = $113
 
 - name: Case 7, ineligible too young.
   period: 2024-01
diff --git a/source_conflicts/candidates.yaml b/source_conflicts/candidates.yaml
index e06355446bb..8b36bed506f 100644
--- a/source_conflicts/candidates.yaml
+++ b/source_conflicts/candidates.yaml
@@ -2164,6 +2164,48 @@ candidates:
   state: ruled
   note: Statute text is in the Axiom corpus; registering needs a pdftotext capture of the official instructions
     page.
+- id: us-il:hbwd-premium-earned-1251-unearned-501-cell
+  program: medicaid
+  years:
+    from: 2009
+    type: calendar
+  question: Is the Illinois Health Benefits for Workers with Disabilities premium for countable earned income of
+    $1,251-1,500 and gross unearned income of $501-750 $79, as 89 Ill. Adm. Code 120.510(n)(3) prints, or $69, as
+    the HFS premium chart prints?
+  sources:
+  - kind: regulation
+    citation: 89 Ill. Adm. Code 120.510(n)(3)
+    url: https://ilga.gov/commission/jcar/admincode/089/089001200I05100R.html
+  - kind: form
+    citation: HFS HBWD Premium Chart (one page, June 2009)
+    url: https://hfs.illinois.gov/content/dam/soi/en/web/hfs/medicalprograms/hbwd/documents/hfsweb004.pdf
+  - kind: guidance
+    citation: HFS 3792 (R-03-13), Health Benefits for Workers with Disabilities brochure, premium table
+    url: https://hfs.illinois.gov/medicalprograms/hbwd/hfs3792hbwd.html
+  readings:
+    statute: No statute is supplied; the regulation's table prints 79 for earned income 1251-1500 and unearned
+      income 501-750, in the text effective February 1, 2009 (33 Ill. Reg. 1681) and unchanged by the amendment
+      effective March 25, 2022 (46 Ill. Reg. 5705).
+    other: The HFS premium chart (June 2009) and the HFS 3792 brochure print 69 for the same cell, which PE-US
+      gives (31 + 38).
+  example: Countable earned income of $1,300 and gross unearned income of $600 a month give a $79 premium under the
+    regulation and a $69 premium under the chart and in PE-US.
+  pe_us:
+    follows: conflicting-source
+    code:
+    - policyengine_us/parameters/gov/states/il/hfs/hbwd/premium/earned.yaml
+    - policyengine_us/parameters/gov/states/il/hfs/hbwd/premium/unearned.yaml
+    - policyengine_us/variables/gov/states/il/hfs/hbwd/il_hbwd_premium.py
+    prs:
+    - https://github.com/PolicyEngine/policyengine-us/pull/10372
+  state: ruled
+  note: 'Ruled 2026-10-27 for the regulation''s 79 by the project lead for the Medicaid fixes; the ruling record is
+    https://github.com/PolicyEngine/policyengine-us/pull/10372#issuecomment-6451385205. Under "Regulations are law" the
+    regulation binds, and the written canons have no exception for an apparent typesetting error, so the 69 in the
+    HFS chart and the HFS 3792 brochure does not override it. PE-US gives 69 because its premium adds an earned
+    component (31) and an unearned component (38), which cannot represent a cell that departs from that sum. Issue
+    10471, which encodes the full 21 x 21 table, will make PE-US follow the ruling. The other 440 cells of the
+    regulation and the chart agree.'
 - id: us-il:joint-childless-eitc-dependency-skip
   program: income-tax
   years: