diff --git a/backend/app/api/endpoints/portfolio.py b/backend/app/api/endpoints/portfolio.py
index 821684e..63b274f 100644
--- a/backend/app/api/endpoints/portfolio.py
+++ b/backend/app/api/endpoints/portfolio.py
@@ -796,6 +796,32 @@ async def sync_portfolio(db: AsyncSession = Depends(get_db), force: bool = True)
             # 이뤄져야 하므로(Portfolio SELECT → UPDATE/DELETE → commit) 큐로 분리가 어려움.
             # sync_portfolio()는 API 엔드포인트(get_db 의존성) 경로에서만 호출되므로
             # 실시간 콜백/스케줄러 직접 호출과는 성격이 다름.
+            # ActiveTrade 잔량 정합 — 같은 종목에 active 행이 1개뿐일 때만 실제 보유량으로 교정.
+            # (분할매도·수동매도 누락으로 DB 잔량이 실제와 달라지면 다음 청산이 과다매도)
+            try:
+                _held = {h.stock_code: h.quantity for h in new_holdings if h.quantity > 0}
+                _at_rows = (await db.execute(
+                    select(ActiveTrade).where(ActiveTrade.status == "active")
+                )).scalars().all()
+                _by_code: dict[str, list] = {}
+                for _row in _at_rows:
+                    _by_code.setdefault(_row.stock_code, []).append(_row)
+                for _code, _rows in _by_code.items():
+                    if len(_rows) != 1:
+                        continue  # 스윙+DT 혼재 등 → 자동 교정하지 않음
+                    _row = _rows[0]
+                    _actual = _held.get(_code, 0)
+                    if _actual == 0:
+                        _row.status = "closed"
+                        logger.info(f"🧹 ActiveTrade 정리: {_code} 보유 없음 → closed")
+                    elif int(_row.quantity or 0) != _actual:
+                        logger.info(
+                            f"🧹 ActiveTrade 잔량 교정: {_code} {_row.quantity} → {_actual}"
+                        )
+                        _row.quantity = _actual
+            except Exception as _rec_err:
+                logger.warning(f"ActiveTrade 정합 실패(무시): {_rec_err}")
+
             await db.commit()
             portfolio_cache.holdings = [h for h in new_holdings if h.quantity > 0]
             await portfolio_cache.cache_summary(balance_data, overseas_balance_data)  # 국내·해외 잔고 전달
@@ -1528,6 +1554,7 @@ class ActiveTradeStatusUpdateRequest(BaseModel):
     reason: Optional[str] = ""
     updated_at: Optional[str] = None
     remaining_pct: Optional[float] = None  # 부분 매도 후 잔여 비율 (예: 0.5). 제공 시 ActiveTrade.remaining_pct 갱신
+    quantity: Optional[int] = None  # 실제 보유 수량으로 교정 (DB 잔량 드리프트 정정용)
 
 
 @router.patch("/active-trades/{stock_code}/status")
@@ -1594,6 +1621,15 @@ async def update_active_trade_status(
         if request.remaining_pct is not None:
             active_trade.remaining_pct = Decimal(str(round(request.remaining_pct, 4)))
 
+        if request.quantity is not None:
+            if request.quantity < 0:
+                raise HTTPException(status_code=400, detail="quantity는 0 이상이어야 합니다")
+            logger.info(
+                f"[TradeMonitor API] {stock_code} ActiveTrade 수량 교정: "
+                f"{active_trade.quantity} → {request.quantity}"
+            )
+            active_trade.quantity = request.quantity
+
         db.add(active_trade)
         await db.commit()
         await db.refresh(active_trade)
diff --git a/backend/tests/test_bugfixes_20260923.py b/backend/tests/test_bugfixes_20260923.py
index 4a45789..071ae6f 100644
--- a/backend/tests/test_bugfixes_20260923.py
+++ b/backend/tests/test_bugfixes_20260923.py
@@ -136,3 +136,21 @@ def test_manual_sell_closes_active_trade():
     src = inspect.getsource(pf.sell_stock)
     assert "_enq_close_at(stock_code" in src
     assert '"quantity": original_holding_qty - quantity' in src
+
+
+def test_sync_reconciles_active_trade_quantity():
+    """동기화가 ActiveTrade 잔량을 실제 보유량으로 정합해야 드리프트가 누적되지 않는다."""
+    import inspect
+    from app.api.endpoints import portfolio as pf
+    src = inspect.getsource(pf.sync_portfolio)
+    assert "ActiveTrade 잔량 교정" in src
+    assert "len(_rows) != 1" in src, "스윙+DT 혼재 종목은 자동 교정 대상에서 제외해야 함"
+    assert "_row.status = \"closed\"" in src, "보유 없음 → closed 처리 누락"
+
+
+def test_active_trade_patch_supports_quantity():
+    import inspect
+    from app.api.endpoints import portfolio as pf
+    assert "quantity" in pf.ActiveTradeStatusUpdateRequest.model_fields
+    src = inspect.getsource(pf.update_active_trade_status)
+    assert "active_trade.quantity = request.quantity" in src