diff --git a/src/PolyTrader.Modules.CopyTrading/Logic/DemoModel.cs b/src/PolyTrader.Modules.CopyTrading/Logic/DemoModel.cs
new file mode 100644
index 0000000..390e978
--- /dev/null
+++ b/src/PolyTrader.Modules.CopyTrading/Logic/DemoModel.cs
@@ -0,0 +1,40 @@
+using System;
+
+namespace PolyTrader.Modules.CopyTrading.Logic
+{
+    /// <summary>
+    /// Reine Logik für einen realistischeren Demo-Modus (Phase 4.2). Demo füllte bisher zum
+    /// Signalpreis ohne Slippage/Fees → Ergebnisse systematisch geschönt und als Validierung
+    /// neuer Master unbrauchbar. Hier: Exit-Fill mit halbem Spread + Fees (aus <see cref="FeeModel"/>),
+    /// damit Demo- und Live-PnL grob vergleichbar werden.
+    /// </summary>
+    public static class DemoModel
+    {
+        /// <summary>Fallback-Halbspread (¢), wenn kein Orderbuch verfügbar ist (Phase 1.2).</summary>
+        public const decimal FallbackHalfSpread = 0.005m;
+
+        /// <summary>
+        /// Simulierter SELL-Fill-Preis im Demo: der Verkäufer trifft den Bid, also unter dem
+        /// Signalpreis um den halben Spread. Auf [0.01, 0.99] geclamped.
+        /// </summary>
+        public static decimal ExitFillPrice(decimal signalPrice, decimal halfSpread)
+        {
+            decimal p = signalPrice - halfSpread;
+            return Math.Clamp(p, 0.01m, 0.99m);
+        }
+
+        /// <summary>
+        /// Realistischer Demo-Close: Erlös zum (leicht schlechteren) Fill-Preis, minus Round-Trip-Fee
+        /// (Entry- und Exit-Leg). Liefert (exitUsd, realizedPnl, totalFees).
+        /// </summary>
+        public static (decimal exitUsd, decimal realizedPnl, decimal totalFees) CloseWithFees(
+            decimal size, decimal signalPrice, decimal entryAmountUsd, int feeBps, decimal halfSpread)
+        {
+            decimal exitPrice = ExitFillPrice(signalPrice, halfSpread);
+            decimal exitUsd = size * exitPrice;
+            decimal totalFees = FeeModel.FeeUsd(entryAmountUsd, feeBps) + FeeModel.FeeUsd(exitUsd, feeBps);
+            decimal realizedPnl = exitUsd - entryAmountUsd - totalFees;
+            return (exitUsd, realizedPnl, totalFees);
+        }
+    }
+}
diff --git a/src/PolyTrader.Modules.CopyTrading/Services/CopyTradingEngine.cs b/src/PolyTrader.Modules.CopyTrading/Services/CopyTradingEngine.cs
index a5057fd..8300887 100644
--- a/src/PolyTrader.Modules.CopyTrading/Services/CopyTradingEngine.cs
+++ b/src/PolyTrader.Modules.CopyTrading/Services/CopyTradingEngine.cs
@@ -633,8 +633,14 @@ namespace PolyTraderSharp.Services
                         {
                             _positionRepo.DeleteDemo(account.AccountId, signal.TokenId);
 
-                            decimal exitUsd = TradeMath.ExitValue(openPos.Size, signal.Price);
-                            decimal realizedPnl = TradeMath.RealizedPnl(openPos.Size, signal.Price, openPos.AmountUsd);
+                            // Phase 4.2: realistischer Demo-Close (Exit-Slippage + Fees), statt zum
+                            // Signalpreis ohne Kosten – sonst ist Demo als Master-Validierung wertlos.
+                            int demoFeeBps = _state.MarketCache.TryGetValue(signal.TokenId, out var demoMd)
+                                ? (demoMd.TakerFeeBps > 0 ? demoMd.TakerFeeBps : FeeModel.FallbackBps(demoMd.Category))
+                                : FeeModel.FallbackBps(null);
+                            var (exitUsd, realizedPnl, totalFees) = DemoModel.CloseWithFees(
+                                openPos.Size, signal.Price, openPos.AmountUsd, demoFeeBps, DemoModel.FallbackHalfSpread);
+                            decimal demoExitPrice = DemoModel.ExitFillPrice(signal.Price, DemoModel.FallbackHalfSpread);
 
                             _state.GlobalPnl += realizedPnl;
                             account.UpdateBalance(account.AvailableBalance + exitUsd);
@@ -652,10 +658,11 @@ namespace PolyTraderSharp.Services
                                 Outcome = signal.Outcome,
                                 Side = signal.Side,
                                 EntryPrice = openPos.EntryPrice,
-                                ExitPrice = signal.Price,
+                                ExitPrice = demoExitPrice,
                                 Size = openPos.Size,
                                 RealizedPnl = realizedPnl,
                                 PnlPercent = TradeMath.PnlPercent(realizedPnl, openPos.AmountUsd),
+                                TotalFees = totalFees,
                                 OpenedAt = openPos.OpenedAt,
                                 ClosedAt = DateTime.UtcNow,
                                 ExitReason = signal.Reason
diff --git a/tests/PolyTrader.Tests/DemoModelTests.cs b/tests/PolyTrader.Tests/DemoModelTests.cs
new file mode 100644
index 0000000..6ed1f20
--- /dev/null
+++ b/tests/PolyTrader.Tests/DemoModelTests.cs
@@ -0,0 +1,48 @@
+using PolyTrader.Modules.CopyTrading.Logic;
+using Xunit;
+using static PolyTrader.Modules.CopyTrading.Logic.DemoModel;
+
+namespace PolyTrader.Tests
+{
+    /// <summary>
+    /// Sicherheitsnetz für den realistischeren Demo-Modus (Phase 4.2): Exit-Slippage + Fees.
+    /// </summary>
+    public class DemoModelTests
+    {
+        [Fact]
+        public void ExitFillPrice_is_below_signal_by_half_spread()
+        {
+            Assert.Equal(0.495m, ExitFillPrice(0.50m, 0.005m));
+        }
+
+        [Theory]
+        [InlineData(0.011, 0.005, 0.01)]  // Clamp Untergrenze
+        [InlineData(0.20, 0.30, 0.01)]    // stark negativ -> Untergrenze
+        [InlineData(0.90, 0.005, 0.895)]  // normal im Band
+        [InlineData(0.999, 0.005, 0.99)]  // Clamp Obergrenze (0.994 -> 0.99)
+        public void ExitFillPrice_clamps_to_valid_range(double signal, double half, double expected)
+        {
+            Assert.Equal((decimal)expected, ExitFillPrice((decimal)signal, (decimal)half));
+        }
+
+        [Fact]
+        public void CloseWithFees_subtracts_slippage_and_roundtrip_fee()
+        {
+            // size 100, signal 0.60 -> exit 0.595, exitUsd 59.5
+            // fees = 1% von 50 (Entry) + 1% von 59.5 (Exit) = 0.5 + 0.595 = 1.095
+            // pnl = 59.5 - 50 - 1.095 = 8.405
+            var (exitUsd, pnl, fees) = CloseWithFees(size: 100m, signalPrice: 0.60m, entryAmountUsd: 50m, feeBps: 100, halfSpread: 0.005m);
+            Assert.Equal(59.5m, exitUsd);
+            Assert.Equal(1.095m, fees);
+            Assert.Equal(8.405m, pnl);
+        }
+
+        [Fact]
+        public void CloseWithFees_zero_fee_only_slippage()
+        {
+            var (exitUsd, pnl, fees) = CloseWithFees(100m, 0.60m, 50m, feeBps: 0, halfSpread: 0.005m);
+            Assert.Equal(0m, fees);
+            Assert.Equal(exitUsd - 50m, pnl);
+        }
+    }
+}