diff --git a/src/dotnet/QuantEngine.Application/Services/FactorComputationService.cs b/src/dotnet/QuantEngine.Application/Services/FactorComputationService.cs
new file mode 100644
index 00000000..d4e9795f
--- /dev/null
+++ b/src/dotnet/QuantEngine.Application/Services/FactorComputationService.cs
@@ -0,0 +1,76 @@
+using System.Text.Json;
+using QuantEngine.Core.Domain;
+using QuantEngine.Core.Interfaces;
+
+namespace QuantEngine.Application.Services;
+
+public sealed record FactorComputationAudit(
+    string Ticker,
+    int StockBars,
+    int IndexBars,
+    string State,
+    DateTimeOffset ComputedAt,
+    string? SourceVersion);
+
+public sealed class FactorComputationService
+{
+    private readonly HistoryIngestionService _history;
+    private readonly string _auditRoot;
+
+    public FactorComputationService(HistoryIngestionService history)
+    {
+        _history = history;
+        _auditRoot = FindRepoTempRoot();
+    }
+
+    private static string FindRepoTempRoot()
+    {
+        var current = new DirectoryInfo(AppContext.BaseDirectory);
+        while (current != null)
+        {
+            if (Directory.Exists(Path.Combine(current.FullName, ".git")))
+            {
+                return Path.Combine(current.FullName, "Temp", "factor_audit");
+            }
+            current = current.Parent;
+        }
+
+        return Path.Combine(Directory.GetCurrentDirectory(), "Temp", "factor_audit");
+    }
+
+    private void AppendAudit(FactorComputationAudit audit)
+    {
+        Directory.CreateDirectory(_auditRoot);
+        var path = Path.Combine(_auditRoot, $"{audit.Ticker}.jsonl");
+        File.AppendAllText(path, JsonSerializer.Serialize(audit, new JsonSerializerOptions { WriteIndented = false }) + Environment.NewLine);
+    }
+
+    public FactorOutputs Compute(
+        string ticker,
+        List<PriceHistoryDailyRecord> stockBars,
+        List<PriceHistoryDailyRecord> indexBars,
+        string? sourceVersion = null)
+    {
+        var computedAt = DateTimeOffset.UtcNow;
+        var outputs = FactorCalculator.CalculateFactors(stockBars, indexBars);
+        AppendAudit(new FactorComputationAudit(ticker, stockBars.Count, indexBars.Count, "SUCCEEDED", computedAt, sourceVersion));
+        return outputs;
+    }
+
+    public async Task AppendFactorOutputsAsync(
+        string ticker,
+        string sourceVersion,
+        FactorOutputs outputs,
+        DateTimeOffset? observedAt = null)
+    {
+        var when = observedAt ?? DateTimeOffset.UtcNow;
+        await _history.AppendFactorOutputAsync("momentum_20d", sourceVersion, outputs.Momentum20D, "PASS", sourceVersion, when);
+        await _history.AppendFactorOutputAsync("momentum_60d", sourceVersion, outputs.Momentum60D, "PASS", sourceVersion, when);
+        await _history.AppendFactorOutputAsync("momentum_120d", sourceVersion, outputs.Momentum120D, "PASS", sourceVersion, when);
+        await _history.AppendFactorOutputAsync("atr_20pct", sourceVersion, outputs.Atr20Pct, "PASS", sourceVersion, when);
+        await _history.AppendFactorOutputAsync("stdev_20d", sourceVersion, outputs.StDev20D, "PASS", sourceVersion, when);
+        await _history.AppendFactorOutputAsync("beta_60d", sourceVersion, outputs.Beta60D, "PASS", sourceVersion, when);
+        await _history.AppendFactorOutputAsync("rs_20d", sourceVersion, outputs.Rs20D, "PASS", sourceVersion, when);
+        AppendAudit(new FactorComputationAudit(ticker, 0, 0, "PERSISTED", when, sourceVersion));
+    }
+}
diff --git a/src/dotnet/QuantEngine.Core.Tests/FactorComputationServiceTests.cs b/src/dotnet/QuantEngine.Core.Tests/FactorComputationServiceTests.cs
new file mode 100644
index 00000000..f0998ca0
--- /dev/null
+++ b/src/dotnet/QuantEngine.Core.Tests/FactorComputationServiceTests.cs
@@ -0,0 +1,53 @@
+using System.Collections.Generic;
+using System.IO;
+using System.Threading.Tasks;
+using Moq;
+using QuantEngine.Application.Services;
+using QuantEngine.Core.Domain;
+using QuantEngine.Core.Interfaces;
+using Xunit;
+
+namespace QuantEngine.Core.Tests;
+
+public class FactorComputationServiceTests
+{
+    [Fact]
+    public async Task ComputeAndAppendFactorOutputs_WritesAuditAndHistory()
+    {
+        var storeMock = new Mock<IPostgresqlHistoryStore>();
+        storeMock.Setup(s => s.AppendAsync(It.IsAny<string>(), It.IsAny<IDictionary<string, object?>>()))
+            .ReturnsAsync(1);
+
+        var history = new HistoryIngestionService(storeMock.Object);
+        var service = new FactorComputationService(history);
+
+        var root = FindRepoRoot();
+        var auditPath = Path.Combine(root, "Temp", "factor_audit", "005930.jsonl");
+        if (File.Exists(auditPath))
+        {
+            File.Delete(auditPath);
+        }
+
+        var outputs = new FactorOutputs(1, 2, 3, 4, 5, 6, 7);
+        await service.AppendFactorOutputsAsync("005930", "v1", outputs);
+
+        storeMock.Verify(s => s.AppendAsync("factor_output_history", It.IsAny<IDictionary<string, object?>>()), Times.Exactly(7));
+        Assert.True(File.Exists(auditPath));
+        Assert.Contains("PERSISTED", File.ReadAllText(auditPath));
+    }
+
+    private static string FindRepoRoot()
+    {
+        var current = new DirectoryInfo(System.AppContext.BaseDirectory);
+        while (current != null)
+        {
+            if (Directory.Exists(Path.Combine(current.FullName, ".git")))
+            {
+                return current.FullName;
+            }
+            current = current.Parent;
+        }
+
+        throw new InvalidOperationException("Repository root not found.");
+    }
+}