diff --git a/backend/baekje_api.py b/backend/baekje_api.py
index b8ff837..8539291 100644
--- a/backend/baekje_api.py
+++ b/backend/baekje_api.py
@@ -260,3 +260,46 @@ def api_get_balance():
     session = get_baekje_session()
     result = session.get_balance(year if year else None)
     return jsonify(result)
+
+
+@baekje_bp.route('/monthly-sales', methods=['GET'])
+def api_get_monthly_sales():
+    """
+    월간 매출(주문) 합계 조회
+    
+    GET /api/baekje/monthly-sales?year=2026&month=3
+    
+    Returns:
+        {
+            "success": true,
+            "total_amount": 7305877,       // 월간 매출 합계
+            "total_returns": 0,            // 월간 반품 합계
+            "net_amount": 7305877,         // 순매출 (매출 - 반품)
+            "total_paid": 0,               // 월간 입금 합계
+            "ending_balance": 14563978,    // 월말 잔액
+            "prev_balance": 14565453,      // 전월이월금
+            "from_date": "2026-03-01",
+            "to_date": "2026-03-31",
+            "rotate_days": 58.4            // 회전일수
+        }
+    """
+    from datetime import datetime
+    
+    year = flask_request.args.get('year', '').strip()
+    month = flask_request.args.get('month', '').strip()
+    
+    # 기본값: 현재 연월
+    now = datetime.now()
+    if not year:
+        year = now.year
+    else:
+        year = int(year)
+    
+    if not month:
+        month = now.month
+    else:
+        month = int(month)
+    
+    session = get_baekje_session()
+    result = session.get_monthly_sales(year, month)
+    return jsonify(result)