diff --git a/src/GoodWood.Application/Games/ChristmasTree/ChristmasTreeGameLogicService.cs b/src/GoodWood.Application/Games/ChristmasTree/ChristmasTreeGameLogicService.cs
index 7f21801..a646b6f 100644
--- a/src/GoodWood.Application/Games/ChristmasTree/ChristmasTreeGameLogicService.cs
+++ b/src/GoodWood.Application/Games/ChristmasTree/ChristmasTreeGameLogicService.cs
@@ -48,6 +48,7 @@ public class ChristmasTreeGameLogicService : IGameLogicService
             CurrentTeamIndex = 0,
             CurrentPlayerIndexInTeam = 0,
             PlayerIndexPerTeam = playerIndexPerTeam,
+            EnableSumOnce = options.EnableSumOnce,
             EnableContinueOnMiss = options.EnableContinueOnMiss,
             MaxContinueThrows = options.MaxContinueThrows,
             ContinueThrowsRemaining = 0,
@@ -118,6 +119,50 @@ public class ChristmasTreeGameLogicService : IGameLogicService
             return RotateToNextPlayer(model, triggers);
         }
 
+        // Sum mode: second throw — try to cross first+second
+        if (model.IsInSumMode)
+        {
+            int sum = model.FirstThrowValue + pinsKnocked;
+            model = model with { IsInSumMode = false, FirstThrowValue = 0 };
+
+            bool crossedOwnSum = TryCrossNumber(teamTrees, playerTeamIndex, sum);
+            if (crossedOwnSum)
+            {
+                lastThrow = lastThrow with { CrossedOwnTree = true, PinsKnocked = sum };
+                teamTrees[playerTeamIndex] = teamTrees[playerTeamIndex] with
+                {
+                    CrossedOutCount = teamTrees[playerTeamIndex].CrossedOutCount + 1
+                };
+                bool gameEndedSum = CheckGameEndCondition(teamTrees, model.EndCondition);
+                if (gameEndedSum)
+                {
+                    lastThrow = lastThrow with { TriggeredGameEnd = true };
+                    return HandleGameEnd(model, teamTrees, lastThrow, triggers);
+                }
+                model = model with { TeamTrees = teamTrees, LastThrow = lastThrow, IsInContinueMode = false, ContinueThrowsRemaining = 0 };
+                return RotateToNextPlayer(model, triggers);
+            }
+
+            var crossedOpponentsSum = TryCrossFromOpponents(teamTrees, playerTeamIndex, sum);
+            if (crossedOpponentsSum.Count > 0)
+            {
+                lastThrow = lastThrow with { CrossedOpponentTrees = true, OpponentTeamsCrossed = crossedOpponentsSum.ToArray(), PinsKnocked = sum };
+                bool gameEndedSum = CheckGameEndCondition(teamTrees, model.EndCondition);
+                if (gameEndedSum)
+                {
+                    lastThrow = lastThrow with { TriggeredGameEnd = true };
+                    return HandleGameEnd(model, teamTrees, lastThrow, triggers);
+                }
+                model = model with { TeamTrees = teamTrees, LastThrow = lastThrow, IsInContinueMode = false, ContinueThrowsRemaining = 0 };
+                return RotateToNextPlayer(model, triggers);
+            }
+
+            // Sum also not available → miss, rotate
+            lastThrow = lastThrow with { WasMiss = true };
+            model = model with { TeamTrees = teamTrees, LastThrow = lastThrow };
+            return RotateToNextPlayer(model, triggers);
+        }
+
         // Try to cross number from own tree first
         bool crossedOwn = TryCrossNumber(teamTrees, playerTeamIndex, pinsKnocked);
 
@@ -181,6 +226,26 @@ public class ChristmasTreeGameLogicService : IGameLogicService
         // Number not available anywhere = miss
         lastThrow = lastThrow with { WasMiss = true };
 
+        // Sum-once: enter sum mode on first miss (non-gutter)
+        if (model.EnableSumOnce)
+        {
+            model = model with
+            {
+                TeamTrees = teamTrees,
+                LastThrow = lastThrow,
+                IsInSumMode = true,
+                FirstThrowValue = pinsKnocked
+            };
+            return (model, new ThrowResult
+            {
+                PointsScored = pinsKnocked,
+                ShouldRotatePlayer = false,
+                IsGameOver = false,
+                WinnerId = null,
+                Triggers = []
+            });
+        }
+
         if (model.EnableContinueOnMiss)
         {
             return HandleContinueModeThrow(model, teamTrees, lastThrow, pinsKnocked, playerTeamIndex, true);
diff --git a/src/GoodWood.Application/Games/ChristmasTree/ChristmasTreeGameModel.cs b/src/GoodWood.Application/Games/ChristmasTree/ChristmasTreeGameModel.cs
index 4219041..74cf40a 100644
--- a/src/GoodWood.Application/Games/ChristmasTree/ChristmasTreeGameModel.cs
+++ b/src/GoodWood.Application/Games/ChristmasTree/ChristmasTreeGameModel.cs
@@ -40,6 +40,21 @@ public record ChristmasTreeGameModel : IGameModel
     /// </summary>
     public Dictionary<int, int> PlayerIndexPerTeam { get; init; } = new();
 
+    /// <summary>
+    /// Whether sum-once variant is enabled.
+    /// </summary>
+    public bool EnableSumOnce { get; init; }
+
+    /// <summary>
+    /// Whether the current player is in sum mode (waiting for second throw to sum).
+    /// </summary>
+    public bool IsInSumMode { get; set; }
+
+    /// <summary>
+    /// Value of the first throw in sum mode.
+    /// </summary>
+    public int FirstThrowValue { get; set; }
+
     /// <summary>
     /// Whether continue-on-miss variant is enabled.
     /// </summary>
diff --git a/src/GoodWood.Application/Games/ChristmasTree/ChristmasTreeGameSetup.cs b/src/GoodWood.Application/Games/ChristmasTree/ChristmasTreeGameSetup.cs
index 8f914eb..11a33d8 100644
--- a/src/GoodWood.Application/Games/ChristmasTree/ChristmasTreeGameSetup.cs
+++ b/src/GoodWood.Application/Games/ChristmasTree/ChristmasTreeGameSetup.cs
@@ -63,10 +63,15 @@ public record ChristmasTreeGameSetup : GameSetupModelBase
     /// </summary>
     public int MaxContinueThrows { get; init; } = 3;
 
+    /// <summary>
+    /// When enabled, a miss (not gutter) allows one additional throw; the sum is tried.
+    /// </summary>
+    public bool EnableSumOnce { get; init; } = true;
+
     /// <summary>
     /// Condition that triggers game end.
     /// </summary>
-    public GameEndCondition EndCondition { get; init; } = GameEndCondition.AllFivesGone;
+    public GameEndCondition EndCondition { get; init; } = GameEndCondition.TreeCleared;
 
     /// <summary>
     /// Creates a new setup with default values.
@@ -77,7 +82,8 @@ public record ChristmasTreeGameSetup : GameSetupModelBase
         TreeVariant variant = TreeVariant.Beginner,
         bool enableContinueOnMiss = false,
         int maxContinueThrows = 3,
-        GameEndCondition endCondition = GameEndCondition.AllFivesGone,
+        bool enableSumOnce = true,
+        GameEndCondition endCondition = GameEndCondition.TreeCleared,
         IReadOnlyList<GameTeam>? teams = null) => new()
     {
         ThrowMode = throwMode,
@@ -86,6 +92,7 @@ public record ChristmasTreeGameSetup : GameSetupModelBase
         Variant = variant,
         EnableContinueOnMiss = enableContinueOnMiss,
         MaxContinueThrows = maxContinueThrows,
+        EnableSumOnce = enableSumOnce,
         EndCondition = endCondition,
         Teams = teams
     };
diff --git a/src/GoodWood.Web/Components/Game/ChristmasTree/ChristmasTreeSetup.razor b/src/GoodWood.Web/Components/Game/ChristmasTree/ChristmasTreeSetup.razor
index ab88edd..fd6d7ab 100644
--- a/src/GoodWood.Web/Components/Game/ChristmasTree/ChristmasTreeSetup.razor
+++ b/src/GoodWood.Web/Components/Game/ChristmasTree/ChristmasTreeSetup.razor
@@ -30,6 +30,11 @@
             <MudSelectItem Value="GameEndCondition.TreeCleared">Ein Baum komplett leer</MudSelectItem>
         </MudSelect>
 
+        <MudSwitch T="bool"
+                   @bind-Value="_options.EnableSumOnce"
+                   Label="Am Ende 1x Summieren"
+                   Color="Color.Primary" />
+
         <MudSwitch T="bool"
                    @bind-Value="_options.EnableContinueOnMiss"
                    Label="Weiterkegeln bei Fehlwurf"
@@ -111,6 +116,7 @@
             _options = new ChristmasTreeSetupOptions
             {
                 Variant = setup.Variant,
+                EnableSumOnce = setup.EnableSumOnce,
                 EnableContinueOnMiss = setup.EnableContinueOnMiss,
                 MaxContinueThrows = setup.MaxContinueThrows,
                 EndCondition = setup.EndCondition
@@ -154,6 +160,7 @@
         ThrowsPerRound = 1,
         ParticipantsMode = ParticipantsMode.GameLogic,
         Variant = _options.Variant,
+        EnableSumOnce = _options.EnableSumOnce,
         EnableContinueOnMiss = _options.EnableContinueOnMiss,
         MaxContinueThrows = _options.MaxContinueThrows,
         EndCondition = _options.EndCondition,
@@ -163,8 +170,9 @@
     private class ChristmasTreeSetupOptions
     {
         public TreeVariant Variant { get; set; } = TreeVariant.Beginner;
+        public bool EnableSumOnce { get; set; } = true;
         public bool EnableContinueOnMiss { get; set; } = false;
         public int MaxContinueThrows { get; set; } = 3;
-        public GameEndCondition EndCondition { get; set; } = GameEndCondition.AllFivesGone;
+        public GameEndCondition EndCondition { get; set; } = GameEndCondition.TreeCleared;
     }
 }