diff --git a/services/cost/README.md b/services/cost/README.md
index b94d7fc..31e7dd5 100644
--- a/services/cost/README.md
+++ b/services/cost/README.md
@@ -43,7 +43,13 @@ Incremental resources needed for each additional connected vehicle:
 | Medium        | 100-1000       | 5                | 15          |
 | High          | > 1000         | 6                | 20          |
 
-*Based on ~3000 VINs using ~10 cores / 30GB marginal on top of platform base*
+**Derivation (from cec-prd-cluster-1 metrics, 2026-02-05):**
+- Event Hubs: ~90M messages/hour, ~230GB/hour incoming
+- Active VINs: ~3,760
+- AKS cluster usage: ~43 cores / ~219GB RAM
+- Estimated platform base: ~34 cores / ~175GB (ClickHouse, Kafka consumers, services)
+- Per-VIN marginal: (43-34)/3760 ≈ 2.4mc, (219-175)/3760 ≈ 12MB
+- Rounded to 3mc / 10MB for conservative estimate
 
 ### Cost Rates