diff --git a/backend/src/features/vehicles/migrations/006_add_tco_fields.sql b/backend/src/features/vehicles/migrations/006_add_tco_fields.sql
new file mode 100644
index 0000000..0f1e993
--- /dev/null
+++ b/backend/src/features/vehicles/migrations/006_add_tco_fields.sql
@@ -0,0 +1,33 @@
+-- Migration: Add TCO (Total Cost of Ownership) fields to vehicles table
+-- Issue: #15
+
+ALTER TABLE vehicles
+  ADD COLUMN IF NOT EXISTS purchase_price DECIMAL(12,2),
+  ADD COLUMN IF NOT EXISTS purchase_date DATE,
+  ADD COLUMN IF NOT EXISTS insurance_cost DECIMAL(10,2),
+  ADD COLUMN IF NOT EXISTS insurance_interval VARCHAR(20),
+  ADD COLUMN IF NOT EXISTS registration_cost DECIMAL(10,2),
+  ADD COLUMN IF NOT EXISTS registration_interval VARCHAR(20),
+  ADD COLUMN IF NOT EXISTS tco_enabled BOOLEAN DEFAULT false;
+
+-- Add CHECK constraints to enforce valid interval values
+ALTER TABLE vehicles
+  ADD CONSTRAINT chk_insurance_interval
+    CHECK (insurance_interval IS NULL OR insurance_interval IN ('monthly', 'semi_annual', 'annual'));
+
+ALTER TABLE vehicles
+  ADD CONSTRAINT chk_registration_interval
+    CHECK (registration_interval IS NULL OR registration_interval IN ('monthly', 'semi_annual', 'annual'));
+
+-- Add CHECK constraints for non-negative costs
+ALTER TABLE vehicles
+  ADD CONSTRAINT chk_purchase_price_non_negative
+    CHECK (purchase_price IS NULL OR purchase_price >= 0);
+
+ALTER TABLE vehicles
+  ADD CONSTRAINT chk_insurance_cost_non_negative
+    CHECK (insurance_cost IS NULL OR insurance_cost >= 0);
+
+ALTER TABLE vehicles
+  ADD CONSTRAINT chk_registration_cost_non_negative
+    CHECK (registration_cost IS NULL OR registration_cost >= 0);