diff --git a/src/seed.py b/src/seed.py
new file mode 100644
index 0000000..efa00fa
--- /dev/null
+++ b/src/seed.py
@@ -0,0 +1,128 @@
+# src/seed.py
+from sqlalchemy.orm import Session
+from src.models import Category, CategorizationRule, HouseholdMember
+
+DEFAULT_CATEGORIES = [
+    ("Income", None, None),
+    ("Housing", "needs", None),
+    ("Groceries", "needs", None),
+    ("Dining Out", "wants", None),
+    ("Transportation", "needs", None),
+    ("Gas", "needs", None),
+    ("Utilities", "needs", None),
+    ("Insurance", "needs", None),
+    ("Healthcare", "needs", None),
+    ("Entertainment", "wants", None),
+    ("Shopping", "wants", None),
+    ("Subscriptions", "wants", None),
+    ("Personal Care", "wants", None),
+    ("Family", "needs", None),
+    ("Gifts & Donations", "wants", None),
+    ("Debt Payment", "needs", None),
+    ("Savings", "savings", None),
+    ("Transfer", None, None),
+    ("Travel", "wants", None),
+    ("Home", "needs", None),
+    ("Professional Services", "needs", None),
+    ("Uncategorized", None, None),
+]
+
+
+def seed_categories(session: Session) -> None:
+    existing = {c.name for c in session.query(Category).all()}
+    for name, tag, icon in DEFAULT_CATEGORIES:
+        if name not in existing:
+            session.add(Category(name=name, default_tag=tag, icon=icon))
+    session.commit()
+
+
+DEFAULT_RULES = [
+    # Income
+    ("CIMTECHNIQUES", "Income", None, "Andrew", 1),
+    ("OASISBATCH PAYROLL", "Income", None, "Donna", 1),
+    # Transfers
+    ("CHASE CREDIT CRD EPAY", "Transfer", None, None, 1),
+    ("CAPITAL ONE TRANSFER", "Transfer", None, None, 1),
+    ("AMEX EPAYMENT", "Transfer", None, "Donna", 1),
+    ("WAY2SAVE SAVINGS", "Transfer", None, None, 1),
+    ("AMZ_STORECRD_PMT", "Transfer", None, None, 1),
+    # Housing
+    ("FREEDOM MTG PYMTS", "Housing", "needs", None, 5),
+    ("Beaufort County", "Housing", "needs", None, 5),  # property tax
+    # Utilities
+    ("DOMINION ENERGY", "Utilities", "needs", None, 5),
+    ("BEAUFORTJASP.*UTILITY", "Utilities", "needs", None, 5),
+    # Insurance
+    ("FARM BUREAU INS", "Insurance", "needs", None, 5),
+    # Transportation
+    ("VW CREDIT", "Transportation", "needs", None, 5),
+    ("TIDAL WAVE", "Transportation", "needs", None, 5),  # car wash
+    # Debt
+    ("WSFS LOAN", "Debt Payment", "needs", None, 5),
+    ("AXOSADVSERV", "Debt Payment", "needs", None, 5),
+    # Groceries
+    ("PUBLIX|ALDI|PIGGLY WIGGLY|WAL-MART|WM SUPERCENTER|WALMART|TRADER JOE", "Groceries", "needs", None, 10),
+    ("HELLOFRESH", "Groceries", "needs", None, 10),
+    # Dining Out
+    ("CHICK-FIL-A|KFC|MCDONALD|TACO BELL|PANDA EXPRESS|LITTLE CAESARS|CULVERS|WAYBACK|SONIC DRIVE|JERSEY MIKE|COOK OUT|SURCHEROS|CHICKEN SALAD", "Dining Out", "wants", None, 10),
+    # Gas
+    ("CIRCLE K", "Gas", "needs", None, 10),
+    # Subscriptions
+    ("Netflix.com", "Subscriptions", "wants", None, 10),
+    ("Prime Video", "Subscriptions", "wants", None, 10),
+    ("APPLE.COM/BILL", "Subscriptions", "wants", None, 10),
+    ("Patreon", "Subscriptions", "wants", None, 10),
+    ("CBB WORLD", "Subscriptions", "wants", None, 10),
+    ("CLAUDE.AI", "Subscriptions", "wants", None, 10),
+    ("OPENROUTER", "Subscriptions", "wants", None, 10),
+    ("STORJ", "Subscriptions", "wants", None, 10),
+    # Healthcare
+    ("TR COUNSELING|RESOURCE MEDICAL|LABORATORY CORP|BEAUFORT PHCY|MED.*UNI MED|CVS/PHARMACY|WALGREENS", "Healthcare", "needs", None, 10),
+    # Home
+    ("ORKIN|LOWES|SHERWIN-WILLIAMS|GRAYCO HARDWARE|MAKERWORLD", "Home", "needs", None, 10),
+    # Professional Services
+    ("GEOARM|ALARMCLUB", "Professional Services", "needs", None, 10),
+    # Shopping (lower priority - catch-all for Amazon etc.)
+    ("AMAZON", "Shopping", "wants", None, 20),
+    # Personal Care
+    ("BARBERS OF THE LOW", "Personal Care", "wants", None, 10),
+]
+
+
+def seed_default_rules(session: Session) -> None:
+    """Seed default categorization rules. Only adds rules if none exist yet."""
+    existing_count = session.query(CategorizationRule).count()
+    if existing_count > 0:
+        return  # Don't overwrite user's rules
+
+    for pattern, cat_name, tag_override, person_name, priority in DEFAULT_RULES:
+        category = session.query(Category).filter_by(name=cat_name).first()
+        if not category:
+            continue
+
+        attributed_to = None
+        if person_name:
+            attributed_to = session.query(HouseholdMember).filter_by(name=person_name).first()
+            if not attributed_to:
+                continue  # Skip rules requiring a person that doesn't exist yet
+
+        rule = CategorizationRule(
+            pattern=pattern,
+            category_id=category.id,
+            tag_override=tag_override,
+            attributed_to_id=attributed_to.id if attributed_to else None,
+            priority=priority,
+        )
+        session.add(rule)
+
+    session.commit()
+
+
+def seed_household(session: Session, name: str, relationship: str) -> HouseholdMember:
+    existing = session.query(HouseholdMember).filter_by(name=name).first()
+    if existing:
+        return existing
+    member = HouseholdMember(name=name, relationship=relationship)
+    session.add(member)
+    session.commit()
+    return member
diff --git a/tests/test_seed.py b/tests/test_seed.py
new file mode 100644
index 0000000..4dc2a7d
--- /dev/null
+++ b/tests/test_seed.py
@@ -0,0 +1,82 @@
+# tests/test_seed.py
+from sqlalchemy import create_engine
+from sqlalchemy.orm import Session
+
+from src.db import Base
+from src.seed import seed_categories, seed_household, seed_default_rules, DEFAULT_CATEGORIES
+from src.models import Category, HouseholdMember, CategorizationRule
+
+
+def make_session():
+    engine = create_engine("sqlite:///:memory:")
+    Base.metadata.create_all(engine)
+    return Session(engine)
+
+
+def test_seed_categories():
+    session = make_session()
+    seed_categories(session)
+    cats = session.query(Category).all()
+    assert len(cats) == len(DEFAULT_CATEGORIES)
+    names = {c.name for c in cats}
+    assert "Groceries" in names
+    assert "Transfer" in names
+    assert "Income" in names
+
+
+def test_seed_categories_idempotent():
+    session = make_session()
+    seed_categories(session)
+    seed_categories(session)
+    cats = session.query(Category).all()
+    assert len(cats) == len(DEFAULT_CATEGORIES)
+
+
+def test_seed_household():
+    session = make_session()
+    seed_household(session, "Andrew", "self")
+    members = session.query(HouseholdMember).all()
+    assert len(members) == 1
+    assert members[0].name == "Andrew"
+
+
+def test_seed_default_rules():
+    session = make_session()
+    seed_categories(session)
+    member = HouseholdMember(name="Andrew", relationship="self")
+    session.add(member)
+    session.commit()
+
+    seed_default_rules(session)
+    rules = session.query(CategorizationRule).all()
+    assert len(rules) > 20
+
+    # Check some known rules
+    netflix = [r for r in rules if "Netflix" in r.pattern]
+    assert len(netflix) == 1
+    assert netflix[0].category.name == "Subscriptions"
+
+
+def test_seed_default_rules_idempotent():
+    session = make_session()
+    seed_categories(session)
+    member = HouseholdMember(name="Andrew", relationship="self")
+    session.add(member)
+    session.commit()
+
+    seed_default_rules(session)
+    count1 = session.query(CategorizationRule).count()
+    seed_default_rules(session)
+    count2 = session.query(CategorizationRule).count()
+    assert count1 == count2
+
+
+def test_seed_default_rules_skips_person_rules_without_members():
+    session = make_session()
+    seed_categories(session)
+    # Don't add any household members
+    seed_default_rules(session)
+    rules = session.query(CategorizationRule).all()
+    # Rules requiring person attribution should be skipped
+    person_rules = [r for r in rules if r.attributed_to_id is not None]
+    assert len(person_rules) == 0