diff --git a/docs/永期对冲计算器.md b/docs/永期对冲计算器.md
index 1de6630..af2f403 100644
--- a/docs/永期对冲计算器.md
+++ b/docs/永期对冲计算器.md
@@ -65,6 +65,19 @@ API：`POST /api/calculator/perp-options`
 组合净利 = 期权净利 + 永续亏损
 ```
 
+**C · 横盘（最大亏损）**
+
+波动≈0、期权到期无内在价值：
+
+```text
+永续盈亏 ≈ 0
+永续开平手续费 = 2 × 现价 × 1 × 0.05%   （同价开平）
+最大亏损 = 权利金总额 + 永续开平手续费
+组合净利 = −最大亏损
+```
+
+忽略资金费 / Theta 过程中的中间态；口径与「权利金按全亏」一致。
+
 ### 手测示例
 
 现价 1800、波动 50 点、目标盈利 15、期权杠杆 100、永续杠杆 10：
@@ -126,6 +139,7 @@ move = (目标 + 权利金) / (期权币数 − 1)
 |------|----------------|
 | A 永续方向对（净利=15） | ≈52.83 |
 | B 组合净利=15 | 51.00 |
+| C 横盘最大亏损 | 37.80（权利金 36 + 同价开平费 1.8） |
 
 ---
 
diff --git a/lib/hub/hub_perp_options_calc_lib.py b/lib/hub/hub_perp_options_calc_lib.py
index 87ae060..91b946a 100644
--- a/lib/hub/hub_perp_options_calc_lib.py
+++ b/lib/hub/hub_perp_options_calc_lib.py
@@ -75,6 +75,25 @@ def _move_for_perp_correct(*, spot: float, target: float, premium: float, fee_ra
     return (float(target) + float(premium) + 2.0 * float(spot) * float(fee_rate)) / denom
 
 
+def _case_sideways(*, spot: float, premium_total: float) -> dict[str, Any]:
+    """横盘/到期无方向:永续≈0,期权权利金全亏,另计永续开平同价手续费.
+
+    最大亏损(正数) = 权利金总额 + 开平手续费(exit=entry)
+    组合净利 = −最大亏损
+    """
+    fee_flat = estimate_roundtrip_fee_usdt(spot, spot, qty=PERP_COINS, contract_size=1.0)
+    prem = float(premium_total)
+    max_loss = prem + float(fee_flat)
+    return {
+        "label": "横盘",
+        "perp_pnl_u": 0.0,
+        "premium_u": round(prem, 8),
+        "fee_u": round(float(fee_flat), 8),
+        "max_loss_u": round(max_loss, 8),
+        "net_u": round(-max_loss, 8),
+    }
+
+
 def calc_perp_options_hedge(
     *,
     base: str = "ETH",
@@ -186,6 +205,7 @@ def calc_perp_options_hedge(
             "perp_pnl_u": round(perp_loss, 8),
             "portfolio_net_u": round(portfolio_net, 8),
         },
+        "case_sideways": _case_sideways(spot=s, premium_total=premium_total),
     }, None
 
 
@@ -316,6 +336,7 @@ def calc_perp_options_points(
             "portfolio_error": port_err,
             "premium_u": round(premium_total, 8),
         },
+        "case_sideways": _case_sideways(spot=s, premium_total=premium_total),
     }, None
 
 
diff --git a/manual_trading_hub/static/calculator.js b/manual_trading_hub/static/calculator.js
index 02c7017..6c826a4 100644
--- a/manual_trading_hub/static/calculator.js
+++ b/manual_trading_hub/static/calculator.js
@@ -572,6 +572,35 @@
     }
   }
 
+  function renderSidewaysCase(sw) {
+    sw = sw || {};
+    return (
+      '<section class="calc-po-case">' +
+      "<h4>情景 C · 横盘(最大亏损)</h4>" +
+      '<div class="calc-summary">' +
+      "<div><span>永续盈亏</span><strong>" +
+      fmtU(sw.perp_pnl_u != null ? sw.perp_pnl_u : 0) +
+      "</strong></div>" +
+      "<div><span>权利金(全亏)</span><strong>" +
+      fmt(sw.premium_u, 2) +
+      "U</strong></div>" +
+      "<div><span>永续开平手续费</span><strong>" +
+      fmt(sw.fee_u, 2) +
+      "U</strong></div>" +
+      "<div><span>最大亏损</span><strong class=\"" +
+      pnlClass(sw.net_u) +
+      '">' +
+      fmt(sw.max_loss_u, 2) +
+      "U</strong></div>" +
+      "<div><span>组合净利</span><strong class=\"" +
+      pnlClass(sw.net_u) +
+      '">' +
+      fmtU(sw.net_u) +
+      "</strong></div>" +
+      "</div></section>"
+    );
+  }
+
   function renderPerpOptionsResult(data) {
     const box = $("calc-po-result");
     if (!box) return;
@@ -614,6 +643,11 @@
       "<div><span>永续保证金</span><strong>" +
       fmt(data.perp_margin_u, 2) +
       "U</strong></div>" +
+      "<div><span>横盘最大亏损</span><strong class=\"" +
+      pnlClass((data.case_sideways || {}).net_u) +
+      '">' +
+      fmt((data.case_sideways || {}).max_loss_u, 2) +
+      "U</strong></div>" +
       "<div><span>开仓参考</span><strong>" +
       esc(capitalHint) +
       "</strong></div>" +
@@ -663,7 +697,9 @@
       '">' +
       fmtU(b.portfolio_net_u) +
       "</strong></div>" +
-      "</div></section></div>";
+      "</div></section>" +
+      renderSidewaysCase(data.case_sideways) +
+      "</div>";
   }
 
   function renderPerpOptionsPointsResult(data) {
@@ -743,6 +779,11 @@
       "<div><span>永续保证金</span><strong>" +
       fmt(data.perp_margin_u, 2) +
       "U</strong></div>" +
+      "<div><span>横盘最大亏损</span><strong class=\"" +
+      pnlClass((data.case_sideways || {}).net_u) +
+      '">' +
+      fmt((data.case_sideways || {}).max_loss_u, 2) +
+      "U</strong></div>" +
       "<div><span>开仓参考</span><strong>" +
       esc(capitalHint) +
       "</strong></div>" +
@@ -774,6 +815,7 @@
       "</strong></div>" +
       "</div></section>" +
       caseB +
+      renderSidewaysCase(data.case_sideways) +
       "</div>";
   }
 
diff --git a/manual_trading_hub/static/index.html b/manual_trading_hub/static/index.html
index c307142..97ae43b 100644
--- a/manual_trading_hub/static/index.html
+++ b/manual_trading_hub/static/index.html
@@ -966,7 +966,7 @@
           <div class="calc-pane-split">
             <div class="calc-input-panel">
               <h2>永期对冲计算器</h2>
-              <p class="calc-hint">永续固定 1 币;单币权利金 = 现价 / 期权杠杆;权利金按全亏;只扣永续开平手续费(各 0.05%).「推仓位」由波动反推期权数量;「推点数」按永续:期权比例反推达目标盈利所需波动.</p>
+              <p class="calc-hint">永续固定 1 币;单币权利金 = 现价 / 期权杠杆;权利金按全亏;只扣永续开平手续费(各 0.05%).「推仓位」由波动反推期权数量;「推点数」按永续:期权比例反推达目标盈利所需波动.横盘最大亏损 = 权利金全亏 + 永续开平同价手续费.</p>
               <form id="calc-po-form" class="calc-form">
                 <div class="calc-form-grid">
                   <label class="calc-field">
@@ -1751,7 +1751,7 @@
   <script src="/assets/chart_draw.js?v=20260720-option-day-1600"></script>
   <script src="/assets/chart.js?v=20260720-option-day-1600"></script>
   <script src="/assets/plan.js?v=20260720-autofill"></script>
-  <script src="/assets/calculator.js?v=20260728-po-2dp"></script>
+  <script src="/assets/calculator.js?v=20260729-po-sideways"></script>
   <script src="/assets/compare.js?v=20260723-compare"></script>
   <script src="/assets/trade_stats_calendar.js?v=3"></script>
   <script src="/assets/archive.js?v=20260724-opt-archive"></script>
diff --git a/tests/test_hub_perp_options_calc_lib.py b/tests/test_hub_perp_options_calc_lib.py
index be227d7..2787ff1 100644
--- a/tests/test_hub_perp_options_calc_lib.py
+++ b/tests/test_hub_perp_options_calc_lib.py
@@ -38,6 +38,11 @@ class HubPerpOptionsCalcTests(unittest.TestCase):
         self.assertAlmostEqual(data["case_b"]["portfolio_net_u"], coins * 32.0 - 50.0, places=6)
         self.assertAlmostEqual(data["perp_margin_u"], 180.0, places=6)
         self.assertTrue(data["capital_ok"])
+        sw = data["case_sideways"]
+        self.assertAlmostEqual(sw["premium_u"], data["premium_total_u"], places=6)
+        self.assertAlmostEqual(sw["fee_u"], 1.8, places=6)
+        self.assertAlmostEqual(sw["max_loss_u"], data["premium_total_u"] + 1.8, places=6)
+        self.assertAlmostEqual(sw["net_u"], -sw["max_loss_u"], places=6)
 
     def test_pct_mode(self):
         data, err = calc_perp_options_hedge(
@@ -113,6 +118,12 @@ class HubPerpOptionsCalcTests(unittest.TestCase):
         # 组合净利=目标: (15+36)/(2-1) = 51
         self.assertAlmostEqual(data["case_b"]["move_points_portfolio"], 51.0, places=6)
         self.assertAlmostEqual(data["case_b"]["portfolio_net_u"], 15.0, places=6)
+        # 横盘:权利金36 + 同价开平费 2*1800*0.0005=1.8 → 37.8
+        sw = data["case_sideways"]
+        self.assertAlmostEqual(sw["premium_u"], 36.0, places=6)
+        self.assertAlmostEqual(sw["fee_u"], 1.8, places=6)
+        self.assertAlmostEqual(sw["max_loss_u"], 37.8, places=6)
+        self.assertAlmostEqual(sw["net_u"], -37.8, places=6)
 
     def test_points_ratio_1_to_1_no_portfolio(self):
         data, err = calc_perp_options(