diff --git a/packages/web/src/app/api/orgs/[orgSlug]/dashboard/sessions/[sessionId]/route.ts b/packages/web/src/app/api/orgs/[orgSlug]/dashboard/sessions/[sessionId]/route.ts
index 35486b8..1151f08 100644
--- a/packages/web/src/app/api/orgs/[orgSlug]/dashboard/sessions/[sessionId]/route.ts
+++ b/packages/web/src/app/api/orgs/[orgSlug]/dashboard/sessions/[sessionId]/route.ts
@@ -43,18 +43,25 @@ export async function GET(
       return forbiddenByRole(access.role, '본인 세션만 열람 가능')
     }
 
-    const totalInput = session.usageRecords.reduce((sum, r) => sum + r.inputTokens, 0)
-    const totalOutput = session.usageRecords.reduce((sum, r) => sum + r.outputTokens, 0)
-    const totalCost = session.usageRecords.reduce((sum, r) => sum + (r.estimatedCostUsd ?? 0), 0)
-
-    const usageTimeline: SessionTimelineUsage[] = session.usageRecords.map((r) => ({
-      timestamp: r.timestamp.toISOString(),
-      inputTokens: r.inputTokens,
-      outputTokens: r.outputTokens,
-      estimatedCostUsd: r.estimatedCostUsd ?? 0,
-      model: r.model,
-      isSubagent: r.isSubagent,
-    }))
+    let totalInput = 0
+    let totalOutput = 0
+    let totalCost = 0
+    const usageTimeline: SessionTimelineUsage[] = new Array(session.usageRecords.length)
+
+    for (let i = 0; i < session.usageRecords.length; i++) {
+      const r = session.usageRecords[i]
+      totalInput += r.inputTokens
+      totalOutput += r.outputTokens
+      totalCost += r.estimatedCostUsd ?? 0
+      usageTimeline[i] = {
+        timestamp: r.timestamp.toISOString(),
+        inputTokens: r.inputTokens,
+        outputTokens: r.outputTokens,
+        estimatedCostUsd: r.estimatedCostUsd ?? 0,
+        model: r.model,
+        isSubagent: r.isSubagent,
+      }
+    }
 
     // 각 UsageRecord를 "직전 ASSISTANT 턴"에 귀속시켜 메시지별 토큰/비용/모델 집계.
     // TOOL 메시지는 건너뛰고 가장 가까운 선행 ASSISTANT로 타고 올라감.
diff --git a/packages/web/src/app/api/orgs/[orgSlug]/dashboard/sessions/route.ts b/packages/web/src/app/api/orgs/[orgSlug]/dashboard/sessions/route.ts
index 25fbe70..7d6a4d4 100644
--- a/packages/web/src/app/api/orgs/[orgSlug]/dashboard/sessions/route.ts
+++ b/packages/web/src/app/api/orgs/[orgSlug]/dashboard/sessions/route.ts
@@ -33,14 +33,17 @@ const sessionInclude = {
 type SessionWithInclude = Prisma.ClaudeSessionGetPayload<{ include: typeof sessionInclude }>
 
 function getSessionTotals(session: SessionWithInclude) {
-  return {
-    inputTokens: session.usageRecords.reduce((sum, r) => sum + r.inputTokens, 0),
-    outputTokens: session.usageRecords.reduce((sum, r) => sum + r.outputTokens, 0),
-    estimatedCostUsd: session.usageRecords.reduce(
-      (sum, r) => sum + (r.estimatedCostUsd ?? 0),
-      0,
-    ),
+  let inputTokens = 0
+  let outputTokens = 0
+  let estimatedCostUsd = 0
+
+  for (const r of session.usageRecords) {
+    inputTokens += r.inputTokens
+    outputTokens += r.outputTokens
+    estimatedCostUsd += r.estimatedCostUsd ?? 0
   }
+
+  return { inputTokens, outputTokens, estimatedCostUsd }
 }
 
 function mapSessionItem(session: SessionWithInclude): SessionItem {