diff --git a/changelog.d/fix-9815-wi-works-cmc-age.fixed.md b/changelog.d/fix-9815-wi-works-cmc-age.fixed.md
new file mode 100644
index 00000000000..c825395c7cb
--- /dev/null
+++ b/changelog.d/fix-9815-wi-works-cmc-age.fixed.md
@@ -0,0 +1 @@
+Compare the Wisconsin Works Custodial Parent of an Infant (CMC) age limit with the child's age in weeks, and set the limit to 12 weeks before 2012 and 8 weeks from 2012, so children aged 1 and 2 no longer get the CMC placement and its $673 grant.
diff --git a/policyengine_us/parameters/gov/states/wi/dcf/works/placement/cmc_infant_age_limit.yaml b/policyengine_us/parameters/gov/states/wi/dcf/works/placement/cmc_infant_age_limit.yaml
index cf3cedce366..7d2dd6de374 100644
--- a/policyengine_us/parameters/gov/states/wi/dcf/works/placement/cmc_infant_age_limit.yaml
+++ b/policyengine_us/parameters/gov/states/wi/dcf/works/placement/cmc_infant_age_limit.yaml
@@ -1,15 +1,19 @@
-description: Wisconsin limits the Custodial Parent of Infant placement to parents with children at or below this age in months under the Wisconsin Works program.
+description: Wisconsin limits the Custodial Parent of an Infant placement to custodial parents of children at or below this age in weeks under the Wisconsin Works program.
 
 values:
-  2011-10-01: 2
+  1997-09-01: 12
+  2012-01-01: 8
 
 metadata:
-  unit: month
+  unit: week
   period: month
   label: Wisconsin Works CMC infant age limit
   reference:
-    # Wisconsin statute specifies 8 weeks; 2 months is an approximation.
     - title: Wisconsin Statutes 49.148(1m)(a)1
       href: https://docs.legis.wisconsin.gov/statutes/statutes/49/iii/148
-    - title: W-2 Manual 7.4.5 - Custodial Parent of an Infant
+    - title: 1997-98 Wisconsin Statutes 49.148(1m)(a)
+      href: https://docs.legis.wisconsin.gov/1997/statutes/statutes/49.pdf#page=19
+    - title: "2011 Wisconsin Act 32, sections 1361s and 9408(1d) #page 226,530"
+      href: https://docs.legis.wisconsin.gov/2011/related/acts/32.pdf#page=226
+    - title: W-2 Manual 7.4.3 - Custodial Parent of an Infant (CMC)
       href: https://dcf.wisconsin.gov/manuals/w-2-manual/Production/07/7.4.3_Custodial_Parent_of_an_Infant_CMC_.htm
diff --git a/policyengine_us/tests/policy/baseline/gov/states/wi/dcf/works/integration.yaml b/policyengine_us/tests/policy/baseline/gov/states/wi/dcf/works/integration.yaml
index 1a4539a0f86..c78a5381a52 100644
--- a/policyengine_us/tests/policy/baseline/gov/states/wi/dcf/works/integration.yaml
+++ b/policyengine_us/tests/policy/baseline/gov/states/wi/dcf/works/integration.yaml
@@ -36,7 +36,7 @@
         is_tax_unit_head_or_spouse: true
         tanf_gross_earned_income: 1_000
       person2:
-        age: 0  # Newborn (monthly_age = 0 ≤ 2)
+        age: 0  # Newborn (0 x 52 = 0 weeks ≤ 8)
     spm_units:
       spm_unit:
         members: [person1, person2]
@@ -211,7 +211,7 @@
         is_tax_unit_head_or_spouse: true
         tanf_gross_earned_income: 0
       person2:
-        age: 3  # monthly_age = 3 > 2 threshold
+        age: 3  # 3 x 52 = 156 weeks > 8-week limit
     spm_units:
       spm_unit:
         members: [person1, person2]
@@ -280,3 +280,28 @@
     wi_works_eligible: true
     wi_works_placement: CSJ
     wi_works: 653
+
+- name: Case 12, child aged 1 year (above CMC threshold) gets CSJ.
+  period: 2025-01
+  input:
+    people:
+      person1:
+        age: 27
+        is_tax_unit_head_or_spouse: true
+        tanf_gross_earned_income: 0
+      person2:
+        age: 1  # 1 x 52 = 52 weeks > 8-week limit
+    spm_units:
+      spm_unit:
+        members: [person1, person2]
+        spm_unit_cash_assets: 500
+    households:
+      household:
+        members: [person1, person2]
+        state_code: WI
+  output:
+    # CMC covers a custodial parent of a child 8 weeks old or less
+    # (Wis. Stat. 49.148(1m)(a)1); a 1-year-old gets the $653 CSJ grant.
+    wi_works_eligible: true
+    wi_works_placement: CSJ
+    wi_works: 653
diff --git a/policyengine_us/tests/policy/baseline/gov/states/wi/dcf/works/wi_works_placement.yaml b/policyengine_us/tests/policy/baseline/gov/states/wi/dcf/works/wi_works_placement.yaml
index 24b7f69b8f3..55d0309f1fc 100644
--- a/policyengine_us/tests/policy/baseline/gov/states/wi/dcf/works/wi_works_placement.yaml
+++ b/policyengine_us/tests/policy/baseline/gov/states/wi/dcf/works/wi_works_placement.yaml
@@ -14,7 +14,7 @@
   output:
     wi_works_placement: CSJ
 
-- name: Case 2, CMC with infant under 2 months.
+- name: Case 2, CMC with a newborn.
   period: 2025-01
   input:
     people:
@@ -22,48 +22,179 @@
         age: 25
         is_pregnant: false
       person2:
-        monthly_age: 1
+        age: 0
     households:
       household1:
         members: [person1, person2]
         state_code: WI
   output:
+    # 0 years x 52 = 0 weeks <= 8-week limit (Wis. Stat. 49.148(1m)(a)1)
     wi_works_placement: CMC
 
-- name: Case 3, CMC with infant exactly 2 months.
+- name: Case 3, CMC with an infant 6.5 weeks old.
   period: 2025-01
   input:
     people:
       person1:
         age: 25
       person2:
-        monthly_age: 2
+        age: 0.125
     households:
       household1:
         members: [person1, person2]
         state_code: WI
   output:
+    # 0.125 years x 52 = 6.5 weeks <= 8
     wi_works_placement: CMC
 
-- name: Case 4, CSJ with child over 2 months.
+- name: Case 4, CMC with an infant 56 days old.
   period: 2025-01
   input:
     people:
       person1:
         age: 25
-        # Explicit monthly_age to avoid formula calculation issues
-        monthly_age: 300
       person2:
-        # monthly_age > 2 to exceed CMC threshold
-        monthly_age: 3
+        age: 0.1533
     households:
       household1:
         members: [person1, person2]
         state_code: WI
   output:
+    # 0.1533 years (56 days) x 52 = 7.97 weeks <= 8. W-2 Manual 7.4.3.4
+    # ends CMC on day 56 (7 days x 8 weeks).
+    wi_works_placement: CMC
+
+- name: Case 5, CSJ with an infant 57 days old.
+  period: 2025-01
+  input:
+    people:
+      person1:
+        age: 25
+      person2:
+        age: 0.1561
+    households:
+      household1:
+        members: [person1, person2]
+        state_code: WI
+  output:
+    # 0.1561 years (57 days) x 52 = 8.12 weeks > 8. A 2-month limit would
+    # give CMC here (0.1561 x 12 = 1.87 months).
+    wi_works_placement: CSJ
+
+- name: Case 6, CSJ with an infant 13 weeks old.
+  period: 2025-01
+  input:
+    people:
+      person1:
+        age: 25
+      person2:
+        age: 0.25
+    households:
+      household1:
+        members: [person1, person2]
+        state_code: WI
+  output:
+    # 0.25 years x 52 = 13 weeks > 8
+    wi_works_placement: CSJ
+
+- name: Case 7, CSJ with a child aged 1 year.
+  period: 2025-01
+  input:
+    people:
+      person1:
+        age: 25
+      person2:
+        age: 1
+    households:
+      household1:
+        members: [person1, person2]
+        state_code: WI
+  output:
+    # 1 year x 52 = 52 weeks > 8
+    wi_works_placement: CSJ
+
+- name: Case 8, CSJ with a child aged 2 years.
+  period: 2025-01
+  input:
+    people:
+      person1:
+        age: 25
+      person2:
+        age: 2
+    households:
+      household1:
+        members: [person1, person2]
+        state_code: WI
+  output:
+    # 2 years x 52 = 104 weeks > 8
+    wi_works_placement: CSJ
+
+- name: Case 9, CMC with an infant 10 weeks old in January 2011.
+  period: 2011-01
+  input:
+    people:
+      person1:
+        age: 25
+      person2:
+        age: 0.19
+    households:
+      household1:
+        members: [person1, person2]
+        state_code: WI
+  output:
+    # 0.19 years x 52 = 9.88 weeks <= 12. The limit was 12 weeks until
+    # 2011 Wis. Act 32 cut it to 8 weeks from January 1, 2012.
+    wi_works_placement: CMC
+
+- name: Case 10, CSJ with an infant 10 weeks old in January 2012.
+  period: 2012-01
+  input:
+    people:
+      person1:
+        age: 25
+      person2:
+        age: 0.19
+    households:
+      household1:
+        members: [person1, person2]
+        state_code: WI
+  output:
+    # 0.19 years x 52 = 9.88 weeks > 8
+    wi_works_placement: CSJ
+
+- name: Case 11, CMC with an infant 84 days old in January 2011.
+  period: 2011-01
+  input:
+    people:
+      person1:
+        age: 25
+      person2:
+        age: 0.23
+    households:
+      household1:
+        members: [person1, person2]
+        state_code: WI
+  output:
+    # 0.23 years (84 days) x 52 = 11.96 weeks <= 12
+    wi_works_placement: CMC
+
+- name: Case 12, CSJ with an infant 85 days old in January 2011.
+  period: 2011-01
+  input:
+    people:
+      person1:
+        age: 25
+      person2:
+        age: 0.233
+    households:
+      household1:
+        members: [person1, person2]
+        state_code: WI
+  output:
+    # 0.233 years (85 days) x 52 = 12.12 weeks > 12
     wi_works_placement: CSJ
 
-- name: Case 5, ARP with pregnant person in third trimester.
+- name: Case 13, ARP with pregnant person in third trimester.
   period: 2025-01
   input:
     people:
@@ -78,7 +209,7 @@
   output:
     wi_works_placement: ARP
 
-- name: Case 6, CSJ with pregnant person not in third trimester.
+- name: Case 14, CSJ with pregnant person not in third trimester.
   period: 2025-01
   input:
     people:
@@ -93,7 +224,7 @@
   output:
     wi_works_placement: CSJ
 
-- name: Case 7, CMC takes priority over ARP.
+- name: Case 15, CMC takes priority over ARP.
   period: 2025-01
   input:
     people:
@@ -102,7 +233,7 @@
         is_pregnant: true
         current_pregnancy_month: 8
       person2:
-        monthly_age: 1
+        age: 0
     households:
       household1:
         members: [person1, person2]
diff --git a/policyengine_us/variables/gov/states/wi/dcf/works/wi_works_placement.py b/policyengine_us/variables/gov/states/wi/dcf/works/wi_works_placement.py
index 3460af39cdf..e6df57b3f32 100644
--- a/policyengine_us/variables/gov/states/wi/dcf/works/wi_works_placement.py
+++ b/policyengine_us/variables/gov/states/wi/dcf/works/wi_works_placement.py
@@ -20,15 +20,19 @@ class wi_works_placement(Variable):
     reference = (
         "https://docs.legis.wisconsin.gov/statutes/statutes/49/iii/148",
         "https://dcf.wisconsin.gov/manuals/w-2-manual/Production/07/7.4.1_Community_Service_Jobs_(CSJ).htm",
+        "https://dcf.wisconsin.gov/manuals/w-2-manual/Production/07/7.4.3_Custodial_Parent_of_an_Infant_CMC_.htm",
     )
 
     def formula(spm_unit, period, parameters):
         p = parameters(period).gov.states.wi.dcf.works.placement
         person = spm_unit.members
 
-        # CMC: Custodial Parent of Infant (child <= 8 weeks ≈ 2 months)
-        child_age_months = person("monthly_age", period)
-        has_infant = spm_unit.any(child_age_months <= p.cmc_infant_age_limit)
+        # CMC: Custodial Parent of Infant (child 8 weeks old or less;
+        # 12 weeks before 2012). The limit is in weeks and age is in years.
+        # With age in whole years (as in the microdata), every child aged 0
+        # counts as at or below the limit, so age 0 always gives CMC.
+        age_in_weeks = person("age", period.this_year) * WEEKS_IN_YEAR
+        has_infant = spm_unit.any(age_in_weeks <= p.cmc_infant_age_limit)
 
         # ARP: At Risk Pregnancy (3rd trimester = month 7+)
         is_pregnant = person("is_pregnant", period)