diff --git a/changelog.d/wic-postpartum.fixed.md b/changelog.d/wic-postpartum.fixed.md
new file mode 100644
index 00000000000..dbd9e51f96b
--- /dev/null
+++ b/changelog.d/wic-postpartum.fixed.md
@@ -0,0 +1 @@
+Make only one mother per infant WIC postpartum or breastfeeding, so a grandmother living with her grandchild no longer qualifies.
diff --git a/policyengine_us/tests/policy/baseline/gov/usda/wic/wic_category.yaml b/policyengine_us/tests/policy/baseline/gov/usda/wic/wic_category.yaml
index c22fe7aebfa..1b185be2360 100644
--- a/policyengine_us/tests/policy/baseline/gov/usda/wic/wic_category.yaml
+++ b/policyengine_us/tests/policy/baseline/gov/usda/wic/wic_category.yaml
@@ -119,3 +119,413 @@
     age: 5
   output:
     wic_category: NONE
+
+# 7 CFR 246.2: postpartum women are "women up to six months after termination
+# of pregnancy" and breastfeeding women are "women up to one year postpartum
+# who are breastfeeding their infants", so an infant makes only its own mother
+# postpartum or breastfeeding, not a grandmother who has her own child at home.
+- name: Three generations in separate tax units, only the infant's mother is postpartum
+  period: 2025
+  input:
+    people:
+      grandmother:
+        age: 50
+        is_female: true
+        own_children_in_household: 1
+      mother:
+        age: 25
+        is_female: true
+        own_children_in_household: 1
+      infant:
+        age: 0.2
+    tax_units:
+      grandmother_tax_unit:
+        members: [grandmother]
+      mother_tax_unit:
+        members: [mother, infant]
+    spm_units:
+      spm_unit:
+        members: [grandmother, mother, infant]
+    families:
+      family:
+        members: [grandmother, mother, infant]
+    households:
+      household:
+        members: [grandmother, mother, infant]
+        state_code: TX
+  output:
+    wic_category: [NONE, POSTPARTUM, INFANT]
+
+- name: Three generations in one tax unit, only the youngest mother is postpartum
+  period: 2025
+  input:
+    people:
+      grandmother:
+        age: 50
+        is_female: true
+        own_children_in_household: 1
+      mother:
+        age: 25
+        is_female: true
+        own_children_in_household: 1
+      infant:
+        age: 0.2
+    tax_units:
+      tax_unit:
+        members: [grandmother, mother, infant]
+    spm_units:
+      spm_unit:
+        members: [grandmother, mother, infant]
+    families:
+      family:
+        members: [grandmother, mother, infant]
+    households:
+      household:
+        members: [grandmother, mother, infant]
+        state_code: TX
+  output:
+    wic_category: [NONE, POSTPARTUM, INFANT]
+
+- name: Mother living alone with her infant is postpartum
+  period: 2025
+  input:
+    people:
+      mother:
+        age: 25
+        is_female: true
+        own_children_in_household: 1
+      infant:
+        age: 0.2
+    tax_units:
+      tax_unit:
+        members: [mother, infant]
+    spm_units:
+      spm_unit:
+        members: [mother, infant]
+    families:
+      family:
+        members: [mother, infant]
+    households:
+      household:
+        members: [mother, infant]
+        state_code: TX
+  output:
+    wic_category: [POSTPARTUM, INFANT]
+
+- name: Infant in a tax unit without a mother is matched to the family's youngest mother
+  period: 2025
+  input:
+    people:
+      grandmother:
+        age: 47
+        is_female: true
+        own_children_in_household: 1
+      mother:
+        age: 22
+        is_female: true
+        own_children_in_household: 1
+      infant:
+        age: 0.2
+    tax_units:
+      adults_tax_unit:
+        members: [grandmother, mother]
+      infant_tax_unit:
+        members: [infant]
+    spm_units:
+      spm_unit:
+        members: [grandmother, mother, infant]
+    families:
+      family:
+        members: [grandmother, mother, infant]
+    households:
+      household:
+        members: [grandmother, mother, infant]
+        state_code: TX
+  output:
+    wic_category: [NONE, POSTPARTUM, INFANT]
+
+- name: Breastfeeding mother of an infant aged 0.8 is breastfeeding, the grandmother is not
+  period: 2025
+  input:
+    people:
+      grandmother:
+        age: 50
+        is_female: true
+        own_children_in_household: 1
+      mother:
+        age: 25
+        is_female: true
+        own_children_in_household: 1
+        is_breastfeeding: true
+      infant:
+        age: 0.8
+    tax_units:
+      tax_unit:
+        members: [grandmother, mother, infant]
+    spm_units:
+      spm_unit:
+        members: [grandmother, mother, infant]
+    families:
+      family:
+        members: [grandmother, mother, infant]
+    households:
+      household:
+        members: [grandmother, mother, infant]
+        state_code: TX
+  output:
+    wic_category: [NONE, BREASTFEEDING, INFANT]
+
+- name: Breastfeeding mother of an infant aged 0.2 is breastfeeding, the grandmother is not postpartum
+  period: 2025
+  input:
+    people:
+      grandmother:
+        age: 50
+        is_female: true
+        own_children_in_household: 1
+      mother:
+        age: 25
+        is_female: true
+        own_children_in_household: 1
+        is_breastfeeding: true
+      infant:
+        age: 0.2
+    tax_units:
+      tax_unit:
+        members: [grandmother, mother, infant]
+    spm_units:
+      spm_unit:
+        members: [grandmother, mother, infant]
+    families:
+      family:
+        members: [grandmother, mother, infant]
+    households:
+      household:
+        members: [grandmother, mother, infant]
+        state_code: TX
+  output:
+    wic_category: [NONE, BREASTFEEDING, INFANT]
+
+- name: A breastfeeding mother of an older infant does not take the postpartum match of another mother's younger infant
+  period: 2025
+  input:
+    people:
+      grandmother:
+        age: 38
+        is_female: true
+        own_children_in_household: 2
+        is_breastfeeding: true
+      mother:
+        age: 17
+        is_female: true
+        own_children_in_household: 1
+      aunt:
+        age: 0.8
+      infant:
+        age: 0.2
+    tax_units:
+      tax_unit:
+        members: [grandmother, mother, aunt, infant]
+    spm_units:
+      spm_unit:
+        members: [grandmother, mother, aunt, infant]
+    families:
+      family:
+        members: [grandmother, mother, aunt, infant]
+    households:
+      household:
+        members: [grandmother, mother, aunt, infant]
+        state_code: TX
+  output:
+    wic_category: [BREASTFEEDING, POSTPARTUM, INFANT, INFANT]
+
+- name: Two mothers with their own infants in one tax unit are both postpartum
+  period: 2025
+  input:
+    people:
+      mother_a:
+        age: 24
+        is_female: true
+        own_children_in_household: 1
+      infant_a:
+        age: 0.3
+      mother_b:
+        age: 21
+        is_female: true
+        own_children_in_household: 1
+      infant_b:
+        age: 0.1
+    tax_units:
+      tax_unit:
+        members: [mother_a, infant_a, mother_b, infant_b]
+    spm_units:
+      spm_unit:
+        members: [mother_a, infant_a, mother_b, infant_b]
+    families:
+      family:
+        members: [mother_a, infant_a, mother_b, infant_b]
+    households:
+      household:
+        members: [mother_a, infant_a, mother_b, infant_b]
+        state_code: TX
+  output:
+    wic_category: [POSTPARTUM, INFANT, POSTPARTUM, INFANT]
+
+- name: Father with an infant has no postpartum woman
+  period: 2025
+  input:
+    people:
+      father:
+        age: 30
+        own_children_in_household: 1
+      infant:
+        age: 0.2
+  output:
+    wic_category: [NONE, INFANT]
+
+- name: Mother of an infant aged 0.6 who is not breastfeeding is not postpartum
+  period: 2025
+  input:
+    people:
+      grandmother:
+        age: 50
+        is_female: true
+        own_children_in_household: 1
+      mother:
+        age: 25
+        is_female: true
+        own_children_in_household: 1
+      infant:
+        age: 0.6
+  output:
+    wic_category: [NONE, NONE, INFANT]
+
+# A woman reported as breastfeeding is matched before the tax-unit heuristic:
+# here the grandmother claims the infant, and the infant's mother files alone.
+- name: Breastfeeding mother in her own tax unit keeps her infant claimed by the grandmother
+  period: 2025
+  input:
+    people:
+      grandmother:
+        age: 45
+        is_female: true
+        own_children_in_household: 1
+      mother:
+        age: 20
+        is_female: true
+        is_breastfeeding: true
+      infant:
+        age: 0.3
+    tax_units:
+      grandmother_tax_unit:
+        members: [grandmother, infant]
+      mother_tax_unit:
+        members: [mother]
+    spm_units:
+      spm_unit:
+        members: [grandmother, mother, infant]
+    families:
+      family:
+        members: [grandmother, mother, infant]
+    households:
+      household:
+        members: [grandmother, mother, infant]
+        state_code: TX
+  output:
+    wic_category: [NONE, BREASTFEEDING, INFANT]
+
+# Limitation: a pregnant mother can take the postpartum match (she stays
+# PREGNANT, which comes first), so the other mother is not postpartum.
+- name: Pregnant younger mother takes the match and stays pregnant
+  period: 2025
+  input:
+    people:
+      grandmother:
+        age: 50
+        is_female: true
+        own_children_in_household: 1
+      mother:
+        age: 25
+        is_female: true
+        is_pregnant: true
+        own_children_in_household: 1
+      infant:
+        age: 0.2
+    tax_units:
+      tax_unit:
+        members: [grandmother, mother, infant]
+    spm_units:
+      spm_unit:
+        members: [grandmother, mother, infant]
+    families:
+      family:
+        members: [grandmother, mother, infant]
+    households:
+      household:
+        members: [grandmother, mother, infant]
+        state_code: TX
+  output:
+    wic_category: [NONE, PREGNANT, INFANT]
+
+# Limitation: one infant makes one woman breastfeeding (the youngest).
+- name: Two breastfeeding women and one infant, only the younger is breastfeeding
+  period: 2025
+  input:
+    people:
+      woman_1:
+        age: 30
+        is_female: true
+        is_breastfeeding: true
+      woman_2:
+        age: 25
+        is_female: true
+        is_breastfeeding: true
+      infant:
+        age: 0.5
+    tax_units:
+      tax_unit:
+        members: [woman_1, woman_2, infant]
+    spm_units:
+      spm_unit:
+        members: [woman_1, woman_2, infant]
+    families:
+      family:
+        members: [woman_1, woman_2, infant]
+    households:
+      household:
+        members: [woman_1, woman_2, infant]
+        state_code: TX
+  output:
+    wic_category: [NONE, BREASTFEEDING, INFANT]
+
+# Limitation: in a couple of two women who are both the infant's parents, only
+# one can be postpartum (the younger).
+- name: Two mothers and one infant in one tax unit, only the younger is postpartum
+  period: 2025
+  input:
+    people:
+      parent_1:
+        age: 32
+        is_female: true
+        own_children_in_household: 1
+      parent_2:
+        age: 30
+        is_female: true
+        own_children_in_household: 1
+      infant:
+        age: 0.2
+    tax_units:
+      tax_unit:
+        members: [parent_1, parent_2, infant]
+    spm_units:
+      spm_unit:
+        members: [parent_1, parent_2, infant]
+    families:
+      family:
+        members: [parent_1, parent_2, infant]
+    households:
+      household:
+        members: [parent_1, parent_2, infant]
+        state_code: TX
+  output:
+    wic_category: [NONE, POSTPARTUM, INFANT]
diff --git a/policyengine_us/variables/gov/usda/wic/wic_category.py b/policyengine_us/variables/gov/usda/wic/wic_category.py
index 0953e4ee38d..6f43d0d2855 100644
--- a/policyengine_us/variables/gov/usda/wic/wic_category.py
+++ b/policyengine_us/variables/gov/usda/wic/wic_category.py
@@ -18,20 +18,72 @@ class wic_category(Variable):
     default_value = WICCategory.NONE
     documentation = "Demographic category for the Special Supplemental Nutrition Program for Women, Infants and Children (WIC)"
     label = "WIC demographic category"
-    reference = "https://www.law.cornell.edu/uscode/text/42/1786#b"
+    reference = (
+        "https://www.law.cornell.edu/uscode/text/42/1786#b",
+        "https://www.ecfr.gov/current/title-7/part-246/section-246.2",
+    )
 
     def formula(person, period, parameters):
         pregnant = person("is_pregnant", period)
         mother = person("is_mother", period)
         breastfeeding = person("is_breastfeeding", period)
         age = person("age", period)
-        # Categorize mothers based on the minimum age of children in the SPM unit.
-        min_age_family = person.family.min(age)
+        tax_unit = person.tax_unit
+        family = person.family
+        # 7 CFR 246.2 defines postpartum and breastfeeding women by the time
+        # since their own pregnancy (up to six months and one year), so an
+        # infant makes only its mother postpartum or breastfeeding. Without
+        # parent-child links, match each infant to at most one woman.
+        infant = age < 1
+        young_infant = age < 0.5
+        in_motherless_tax_unit = ~tax_unit.any(mother)
+
+        # 1. A woman reported as breastfeeding is feeding an infant, so match
+        # her first: to an infant in her tax unit, else to any remaining infant
+        # in her family (youngest breastfeeding women first).
+        bf_rank_tax_unit = person.get_rank(tax_unit, age, breastfeeding)
+        bf_in_tax_unit = breastfeeding & (bf_rank_tax_unit < tax_unit.sum(infant))
+        bf_rest = breastfeeding & ~bf_in_tax_unit
+        bf_rank_family = person.get_rank(family, age, bf_rest)
+        family_infants_left = family.sum(infant) - family.sum(bf_in_tax_unit)
+        bf_in_family = bf_rest & (bf_rank_family < family_infants_left)
+        breastfeeding_woman = bf_in_tax_unit | bf_in_family
+
+        # Take the matched infants out of the pools, oldest first, so that
+        # breastfeeding women count against infants aged six months to one
+        # year before younger ones (inputs cannot tell which infant is whose:
+        # a breastfeeding woman and another mother in one tax unit are assumed
+        # to have the older and the younger infant). Family matches take
+        # infants from tax units without a mother first.
+        infant_rank_tax_unit = person.get_rank(tax_unit, -age, infant)
+        taken = infant & (infant_rank_tax_unit < tax_unit.sum(bf_in_tax_unit))
+        left = infant & ~taken
+        infant_rank_family = person.get_rank(
+            family, where(in_motherless_tax_unit, 0, 2) - age, left
+        )
+        taken = taken | (left & (infant_rank_family < family.sum(bf_in_family)))
+        free_young_infant = young_infant & ~taken
+
+        # 2. Match each remaining infant under six months to one other mother
+        # in its tax unit, youngest first, and an infant in a tax unit without
+        # a mother to one of the family's remaining mothers.
+        candidate = mother & ~breastfeeding_woman
+        pp_rank_tax_unit = person.get_rank(tax_unit, age, candidate)
+        pp_in_tax_unit = candidate & (
+            pp_rank_tax_unit < tax_unit.sum(free_young_infant)
+        )
+        pp_rest = candidate & ~pp_in_tax_unit
+        pp_rank_family = person.get_rank(family, age, pp_rest)
+        pp_in_family = pp_rest & (
+            pp_rank_family < family.sum(free_young_infant & in_motherless_tax_unit)
+        )
+        postpartum = pp_in_tax_unit | pp_in_family
+
         return select(
             [
                 pregnant,
-                mother & breastfeeding & (min_age_family < 1),
-                mother & (min_age_family < 0.5),
+                breastfeeding_woman,
+                postpartum,
                 age < 1,
                 age < 5,
             ],