diff --git a/MoneyMap/Models/Api/FinancialAuditModels.cs b/MoneyMap/Models/Api/FinancialAuditModels.cs
new file mode 100644
index 0000000..4f7123e
--- /dev/null
+++ b/MoneyMap/Models/Api/FinancialAuditModels.cs
@@ -0,0 +1,137 @@
+namespace MoneyMap.Models.Api;
+
+/// <summary>
+/// Complete financial audit response for AI analysis.
+/// </summary>
+public class FinancialAuditResponse
+{
+    public DateTime GeneratedAt { get; set; }
+    public DateTime PeriodStart { get; set; }
+    public DateTime PeriodEnd { get; set; }
+
+    public AuditSummary Summary { get; set; } = new();
+    public List<BudgetStatusDto> Budgets { get; set; } = new();
+    public List<CategorySpendingDto> SpendingByCategory { get; set; } = new();
+    public List<MerchantSpendingDto> TopMerchants { get; set; } = new();
+    public List<MonthlyTrendDto> MonthlyTrends { get; set; } = new();
+    public List<AccountSummaryDto> Accounts { get; set; } = new();
+    public List<AuditFlagDto> Flags { get; set; } = new();
+    public List<TransactionDto>? Transactions { get; set; }
+}
+
+/// <summary>
+/// High-level financial statistics for the audit period.
+/// </summary>
+public class AuditSummary
+{
+    public int TotalTransactions { get; set; }
+    public decimal TotalIncome { get; set; }
+    public decimal TotalExpenses { get; set; }
+    public decimal NetCashFlow { get; set; }
+    public decimal AverageDailySpend { get; set; }
+    public int DaysInPeriod { get; set; }
+    public int UncategorizedTransactions { get; set; }
+    public decimal UncategorizedAmount { get; set; }
+}
+
+/// <summary>
+/// Budget status with period information.
+/// </summary>
+public class BudgetStatusDto
+{
+    public int BudgetId { get; set; }
+    public string Category { get; set; } = "";
+    public string Period { get; set; } = "";
+    public decimal Limit { get; set; }
+    public decimal Spent { get; set; }
+    public decimal Remaining { get; set; }
+    public decimal PercentUsed { get; set; }
+    public bool IsOverBudget { get; set; }
+    public string PeriodRange { get; set; } = "";
+}
+
+/// <summary>
+/// Spending breakdown by category with optional budget correlation.
+/// </summary>
+public class CategorySpendingDto
+{
+    public string Category { get; set; } = "";
+    public decimal TotalSpent { get; set; }
+    public int TransactionCount { get; set; }
+    public decimal PercentOfTotal { get; set; }
+    public decimal AverageTransaction { get; set; }
+    public decimal? BudgetLimit { get; set; }
+    public decimal? BudgetRemaining { get; set; }
+    public bool? IsOverBudget { get; set; }
+}
+
+/// <summary>
+/// Spending patterns by merchant.
+/// </summary>
+public class MerchantSpendingDto
+{
+    public string MerchantName { get; set; } = "";
+    public string? Category { get; set; }
+    public decimal TotalSpent { get; set; }
+    public int TransactionCount { get; set; }
+    public decimal AverageTransaction { get; set; }
+    public DateTime FirstTransaction { get; set; }
+    public DateTime LastTransaction { get; set; }
+}
+
+/// <summary>
+/// Monthly income/expense/net trends.
+/// </summary>
+public class MonthlyTrendDto
+{
+    public string Month { get; set; } = "";
+    public int Year { get; set; }
+    public decimal Income { get; set; }
+    public decimal Expenses { get; set; }
+    public decimal NetCashFlow { get; set; }
+    public int TransactionCount { get; set; }
+    public Dictionary<string, decimal> TopCategories { get; set; } = new();
+}
+
+/// <summary>
+/// Per-account transaction summary.
+/// </summary>
+public class AccountSummaryDto
+{
+    public int AccountId { get; set; }
+    public string AccountName { get; set; } = "";
+    public string Institution { get; set; } = "";
+    public string AccountType { get; set; } = "";
+    public int TransactionCount { get; set; }
+    public decimal TotalDebits { get; set; }
+    public decimal TotalCredits { get; set; }
+    public decimal NetFlow { get; set; }
+}
+
+/// <summary>
+/// AI-friendly flag highlighting potential issues or observations.
+/// </summary>
+public class AuditFlagDto
+{
+    public string Type { get; set; } = "";
+    public string Severity { get; set; } = "";
+    public string Message { get; set; } = "";
+    public object? Details { get; set; }
+}
+
+/// <summary>
+/// Simplified transaction for export.
+/// </summary>
+public class TransactionDto
+{
+    public long Id { get; set; }
+    public DateTime Date { get; set; }
+    public string Name { get; set; } = "";
+    public string? Memo { get; set; }
+    public decimal Amount { get; set; }
+    public string? Category { get; set; }
+    public string? MerchantName { get; set; }
+    public string AccountName { get; set; } = "";
+    public string? CardLabel { get; set; }
+    public bool IsTransfer { get; set; }
+}
diff --git a/MoneyMap/Program.cs b/MoneyMap/Program.cs
index 35f7833..db32201 100644
--- a/MoneyMap/Program.cs
+++ b/MoneyMap/Program.cs
@@ -66,6 +66,9 @@ builder.Services.AddScoped<IReceiptParser, AIReceiptParser>();
 // AI categorization service
 builder.Services.AddHttpClient<ITransactionAICategorizer, TransactionAICategorizer>();
 
+// Financial audit API service
+builder.Services.AddScoped<IFinancialAuditService, FinancialAuditService>();
+
 var app = builder.Build();
 
 // Seed default category mappings on startup
@@ -93,4 +96,19 @@ app.UseAuthorization();
 
 app.MapRazorPages();
 
+// Financial Audit API endpoint
+app.MapGet("/api/audit", async (
+    IFinancialAuditService auditService,
+    DateTime? startDate,
+    DateTime? endDate,
+    bool includeTransactions = false) =>
+{
+    var end = endDate ?? DateTime.Today;
+    var start = startDate ?? end.AddDays(-90);
+
+    var result = await auditService.GenerateAuditAsync(start, end, includeTransactions);
+    return Results.Ok(result);
+})
+.WithName("GetFinancialAudit");
+
 app.Run();
diff --git a/MoneyMap/Services/FinancialAuditService.cs b/MoneyMap/Services/FinancialAuditService.cs
new file mode 100644
index 0000000..2cfa2f8
--- /dev/null
+++ b/MoneyMap/Services/FinancialAuditService.cs
@@ -0,0 +1,491 @@
+using Microsoft.EntityFrameworkCore;
+using MoneyMap.Data;
+using MoneyMap.Models;
+using MoneyMap.Models.Api;
+
+namespace MoneyMap.Services;
+
+public interface IFinancialAuditService
+{
+    Task<FinancialAuditResponse> GenerateAuditAsync(
+        DateTime startDate,
+        DateTime endDate,
+        bool includeTransactions = false);
+}
+
+public class FinancialAuditService : IFinancialAuditService
+{
+    private readonly MoneyMapContext _db;
+    private readonly IBudgetService _budgetService;
+
+    public FinancialAuditService(MoneyMapContext db, IBudgetService budgetService)
+    {
+        _db = db;
+        _budgetService = budgetService;
+    }
+
+    public async Task<FinancialAuditResponse> GenerateAuditAsync(
+        DateTime startDate,
+        DateTime endDate,
+        bool includeTransactions = false)
+    {
+        var response = new FinancialAuditResponse
+        {
+            GeneratedAt = DateTime.UtcNow,
+            PeriodStart = startDate.Date,
+            PeriodEnd = endDate.Date
+        };
+
+        // Base query for the period
+        var periodTransactions = _db.Transactions
+            .Include(t => t.Account)
+            .Include(t => t.Card)
+            .Include(t => t.Merchant)
+            .Where(t => t.Date >= startDate.Date && t.Date <= endDate.Date)
+            .AsNoTracking();
+
+        // Calculate all sections in parallel where possible
+        response.Summary = await CalculateSummaryAsync(periodTransactions, startDate, endDate);
+        response.Budgets = await GetBudgetStatusesAsync();
+        response.SpendingByCategory = await GetCategorySpendingAsync(periodTransactions, response.Budgets);
+        response.TopMerchants = await GetMerchantSpendingAsync(periodTransactions);
+        response.MonthlyTrends = await GetMonthlyTrendsAsync(startDate, endDate);
+        response.Accounts = await GetAccountSummariesAsync(periodTransactions);
+        response.Flags = GenerateAuditFlags(response);
+
+        if (includeTransactions)
+        {
+            response.Transactions = await GetTransactionListAsync(periodTransactions);
+        }
+
+        return response;
+    }
+
+    private async Task<AuditSummary> CalculateSummaryAsync(
+        IQueryable<Transaction> transactions,
+        DateTime startDate,
+        DateTime endDate)
+    {
+        // Exclude transfers for spending calculations
+        var nonTransferTxns = transactions.ExcludeTransfers();
+
+        var stats = await nonTransferTxns
+            .GroupBy(_ => 1)
+            .Select(g => new
+            {
+                TotalCount = g.Count(),
+                TotalIncome = g.Where(t => t.Amount > 0).Sum(t => t.Amount),
+                TotalExpenses = g.Where(t => t.Amount < 0).Sum(t => Math.Abs(t.Amount)),
+                UncategorizedCount = g.Count(t => string.IsNullOrEmpty(t.Category)),
+                UncategorizedAmount = g.Where(t => string.IsNullOrEmpty(t.Category) && t.Amount < 0)
+                    .Sum(t => Math.Abs(t.Amount))
+            })
+            .FirstOrDefaultAsync();
+
+        var daysInPeriod = (endDate.Date - startDate.Date).Days + 1;
+
+        return new AuditSummary
+        {
+            TotalTransactions = stats?.TotalCount ?? 0,
+            TotalIncome = stats?.TotalIncome ?? 0,
+            TotalExpenses = stats?.TotalExpenses ?? 0,
+            NetCashFlow = (stats?.TotalIncome ?? 0) - (stats?.TotalExpenses ?? 0),
+            DaysInPeriod = daysInPeriod,
+            AverageDailySpend = daysInPeriod > 0 ? (stats?.TotalExpenses ?? 0) / daysInPeriod : 0,
+            UncategorizedTransactions = stats?.UncategorizedCount ?? 0,
+            UncategorizedAmount = stats?.UncategorizedAmount ?? 0
+        };
+    }
+
+    private async Task<List<BudgetStatusDto>> GetBudgetStatusesAsync()
+    {
+        var statuses = await _budgetService.GetAllBudgetStatusesAsync();
+
+        return statuses.Select(s => new BudgetStatusDto
+        {
+            BudgetId = s.Budget.Id,
+            Category = s.Budget.DisplayName,
+            Period = s.Budget.Period.ToString(),
+            Limit = s.Budget.Amount,
+            Spent = s.Spent,
+            Remaining = s.Remaining,
+            PercentUsed = s.PercentUsed,
+            IsOverBudget = s.IsOverBudget,
+            PeriodRange = s.PeriodDisplay
+        }).ToList();
+    }
+
+    private async Task<List<CategorySpendingDto>> GetCategorySpendingAsync(
+        IQueryable<Transaction> transactions,
+        List<BudgetStatusDto> budgets)
+    {
+        var categorySpending = await transactions
+            .ExcludeTransfers()
+            .Where(t => t.Amount < 0 && !string.IsNullOrEmpty(t.Category))
+            .GroupBy(t => t.Category)
+            .Select(g => new
+            {
+                Category = g.Key,
+                TotalSpent = g.Sum(t => Math.Abs(t.Amount)),
+                Count = g.Count()
+            })
+            .OrderByDescending(x => x.TotalSpent)
+            .ToListAsync();
+
+        var totalSpending = categorySpending.Sum(c => c.TotalSpent);
+
+        // Create a lookup for budget data by category
+        var budgetLookup = budgets
+            .Where(b => b.Category != "Total Spending")
+            .ToDictionary(b => b.Category.ToLowerInvariant(), b => b);
+
+        return categorySpending.Select(c =>
+        {
+            var dto = new CategorySpendingDto
+            {
+                Category = c.Category ?? "Uncategorized",
+                TotalSpent = c.TotalSpent,
+                TransactionCount = c.Count,
+                PercentOfTotal = totalSpending > 0 ? Math.Round(c.TotalSpent / totalSpending * 100, 2) : 0,
+                AverageTransaction = c.Count > 0 ? Math.Round(c.TotalSpent / c.Count, 2) : 0
+            };
+
+            // Add budget correlation if available
+            if (budgetLookup.TryGetValue((c.Category ?? "").ToLowerInvariant(), out var budget))
+            {
+                dto.BudgetLimit = budget.Limit;
+                dto.BudgetRemaining = budget.Remaining;
+                dto.IsOverBudget = budget.IsOverBudget;
+            }
+
+            return dto;
+        }).ToList();
+    }
+
+    private async Task<List<MerchantSpendingDto>> GetMerchantSpendingAsync(
+        IQueryable<Transaction> transactions)
+    {
+        var merchantSpending = await transactions
+            .ExcludeTransfers()
+            .Where(t => t.Amount < 0 && t.MerchantId != null)
+            .GroupBy(t => new { t.MerchantId, t.Merchant!.Name })
+            .Select(g => new
+            {
+                MerchantName = g.Key.Name,
+                Category = g.Max(t => t.Category),
+                TotalSpent = g.Sum(t => Math.Abs(t.Amount)),
+                Count = g.Count(),
+                FirstDate = g.Min(t => t.Date),
+                LastDate = g.Max(t => t.Date)
+            })
+            .OrderByDescending(x => x.TotalSpent)
+            .Take(20)
+            .ToListAsync();
+
+        return merchantSpending.Select(m => new MerchantSpendingDto
+        {
+            MerchantName = m.MerchantName,
+            Category = m.Category,
+            TotalSpent = m.TotalSpent,
+            TransactionCount = m.Count,
+            AverageTransaction = m.Count > 0 ? Math.Round(m.TotalSpent / m.Count, 2) : 0,
+            FirstTransaction = m.FirstDate,
+            LastTransaction = m.LastDate
+        }).ToList();
+    }
+
+    private async Task<List<MonthlyTrendDto>> GetMonthlyTrendsAsync(DateTime startDate, DateTime endDate)
+    {
+        var monthlyData = await _db.Transactions
+            .Where(t => t.Date >= startDate.Date && t.Date <= endDate.Date)
+            .ExcludeTransfers()
+            .GroupBy(t => new { t.Date.Year, t.Date.Month })
+            .Select(g => new
+            {
+                g.Key.Year,
+                g.Key.Month,
+                Income = g.Where(t => t.Amount > 0).Sum(t => t.Amount),
+                Expenses = g.Where(t => t.Amount < 0).Sum(t => Math.Abs(t.Amount)),
+                Count = g.Count()
+            })
+            .OrderBy(x => x.Year)
+            .ThenBy(x => x.Month)
+            .ToListAsync();
+
+        // Get top categories per month
+        var categoryByMonth = await _db.Transactions
+            .Where(t => t.Date >= startDate.Date && t.Date <= endDate.Date)
+            .ExcludeTransfers()
+            .Where(t => t.Amount < 0 && !string.IsNullOrEmpty(t.Category))
+            .GroupBy(t => new { t.Date.Year, t.Date.Month, t.Category })
+            .Select(g => new
+            {
+                g.Key.Year,
+                g.Key.Month,
+                g.Key.Category,
+                Total = g.Sum(t => Math.Abs(t.Amount))
+            })
+            .ToListAsync();
+
+        return monthlyData.Select(m =>
+        {
+            var topCategories = categoryByMonth
+                .Where(c => c.Year == m.Year && c.Month == m.Month)
+                .OrderByDescending(c => c.Total)
+                .Take(5)
+                .ToDictionary(c => c.Category ?? "Other", c => c.Total);
+
+            return new MonthlyTrendDto
+            {
+                Month = $"{m.Year}-{m.Month:D2}",
+                Year = m.Year,
+                Income = m.Income,
+                Expenses = m.Expenses,
+                NetCashFlow = m.Income - m.Expenses,
+                TransactionCount = m.Count,
+                TopCategories = topCategories
+            };
+        }).ToList();
+    }
+
+    private async Task<List<AccountSummaryDto>> GetAccountSummariesAsync(
+        IQueryable<Transaction> transactions)
+    {
+        // Use only mapped columns in the GroupBy, compute DisplayLabel in memory
+        var accountStats = await transactions
+            .GroupBy(t => new {
+                t.AccountId,
+                t.Account.Institution,
+                t.Account.Last4,
+                t.Account.Nickname,
+                t.Account.AccountType
+            })
+            .Select(g => new
+            {
+                g.Key.AccountId,
+                g.Key.Institution,
+                g.Key.Last4,
+                g.Key.Nickname,
+                g.Key.AccountType,
+                Count = g.Count(),
+                Debits = g.Where(t => t.Amount < 0).Sum(t => Math.Abs(t.Amount)),
+                Credits = g.Where(t => t.Amount > 0).Sum(t => t.Amount)
+            })
+            .ToListAsync();
+
+        return accountStats.Select(a => new AccountSummaryDto
+        {
+            AccountId = a.AccountId,
+            AccountName = string.IsNullOrEmpty(a.Nickname)
+                ? $"{a.Institution} {a.Last4} ({a.AccountType})"
+                : $"{a.Nickname} ({a.Institution} {a.Last4})",
+            Institution = a.Institution,
+            AccountType = a.AccountType.ToString(),
+            TransactionCount = a.Count,
+            TotalDebits = a.Debits,
+            TotalCredits = a.Credits,
+            NetFlow = a.Credits - a.Debits
+        }).ToList();
+    }
+
+    private async Task<List<TransactionDto>> GetTransactionListAsync(
+        IQueryable<Transaction> transactions)
+    {
+        // Fetch raw data without computed properties
+        var rawTxns = await transactions
+            .OrderByDescending(t => t.Date)
+            .ThenByDescending(t => t.Id)
+            .Select(t => new
+            {
+                t.Id,
+                t.Date,
+                t.Name,
+                t.Memo,
+                t.Amount,
+                t.Category,
+                MerchantName = t.Merchant != null ? t.Merchant.Name : null,
+                AccountInstitution = t.Account.Institution,
+                AccountLast4 = t.Account.Last4,
+                AccountNickname = t.Account.Nickname,
+                AccountType = t.Account.AccountType,
+                CardIssuer = t.Card != null ? t.Card.Issuer : null,
+                CardLast4 = t.Card != null ? t.Card.Last4 : null,
+                CardNickname = t.Card != null ? t.Card.Nickname : null,
+                IsTransfer = t.TransferToAccountId != null
+            })
+            .ToListAsync();
+
+        // Map to DTOs with computed labels
+        return rawTxns.Select(t => new TransactionDto
+        {
+            Id = t.Id,
+            Date = t.Date,
+            Name = t.Name,
+            Memo = t.Memo,
+            Amount = t.Amount,
+            Category = t.Category,
+            MerchantName = t.MerchantName,
+            AccountName = string.IsNullOrEmpty(t.AccountNickname)
+                ? $"{t.AccountInstitution} {t.AccountLast4} ({t.AccountType})"
+                : $"{t.AccountNickname} ({t.AccountInstitution} {t.AccountLast4})",
+            CardLabel = t.CardIssuer != null
+                ? (string.IsNullOrEmpty(t.CardNickname)
+                    ? $"{t.CardIssuer} {t.CardLast4}"
+                    : $"{t.CardNickname} ({t.CardIssuer} {t.CardLast4})")
+                : null,
+            IsTransfer = t.IsTransfer
+        }).ToList();
+    }
+
+    private List<AuditFlagDto> GenerateAuditFlags(FinancialAuditResponse response)
+    {
+        var flags = new List<AuditFlagDto>();
+
+        // Flag: Over-budget categories
+        foreach (var budget in response.Budgets.Where(b => b.IsOverBudget))
+        {
+            var overBy = budget.Spent - budget.Limit;
+            flags.Add(new AuditFlagDto
+            {
+                Type = "OverBudget",
+                Severity = "Alert",
+                Message = $"{budget.Category} budget exceeded by {overBy:C} ({budget.PercentUsed:F0}% of {budget.Limit:C} limit)",
+                Details = new
+                {
+                    budget.BudgetId,
+                    budget.Category,
+                    budget.Limit,
+                    budget.Spent,
+                    OverAmount = overBy,
+                    budget.PercentUsed
+                }
+            });
+        }
+
+        // Flag: High budget utilization (>80% but not over)
+        foreach (var budget in response.Budgets.Where(b => !b.IsOverBudget && b.PercentUsed >= 80))
+        {
+            flags.Add(new AuditFlagDto
+            {
+                Type = "HighBudgetUtilization",
+                Severity = "Warning",
+                Message = $"{budget.Category} budget at {budget.PercentUsed:F0}% ({budget.Remaining:C} remaining)",
+                Details = new
+                {
+                    budget.BudgetId,
+                    budget.Category,
+                    budget.Limit,
+                    budget.Spent,
+                    budget.Remaining,
+                    budget.PercentUsed
+                }
+            });
+        }
+
+        // Flag: Uncategorized transactions
+        if (response.Summary.UncategorizedTransactions > 0)
+        {
+            flags.Add(new AuditFlagDto
+            {
+                Type = "Uncategorized",
+                Severity = "Warning",
+                Message = $"{response.Summary.UncategorizedTransactions} transactions ({response.Summary.UncategorizedAmount:C}) are uncategorized",
+                Details = new
+                {
+                    Count = response.Summary.UncategorizedTransactions,
+                    Amount = response.Summary.UncategorizedAmount
+                }
+            });
+        }
+
+        // Flag: Negative net cash flow
+        if (response.Summary.NetCashFlow < 0)
+        {
+            flags.Add(new AuditFlagDto
+            {
+                Type = "NegativeCashFlow",
+                Severity = "Alert",
+                Message = $"Spending exceeded income by {Math.Abs(response.Summary.NetCashFlow):C} during this period",
+                Details = new
+                {
+                    response.Summary.TotalIncome,
+                    response.Summary.TotalExpenses,
+                    response.Summary.NetCashFlow
+                }
+            });
+        }
+
+        // Flag: Large single category spending (>30% of total)
+        foreach (var category in response.SpendingByCategory.Where(c => c.PercentOfTotal > 30))
+        {
+            flags.Add(new AuditFlagDto
+            {
+                Type = "HighCategoryConcentration",
+                Severity = "Info",
+                Message = $"{category.Category} accounts for {category.PercentOfTotal:F0}% of total spending ({category.TotalSpent:C})",
+                Details = new
+                {
+                    category.Category,
+                    category.TotalSpent,
+                    category.PercentOfTotal,
+                    category.TransactionCount
+                }
+            });
+        }
+
+        // Flag: Month-over-month spending increases
+        if (response.MonthlyTrends.Count >= 2)
+        {
+            var recentMonths = response.MonthlyTrends.TakeLast(2).ToList();
+            var previousMonth = recentMonths[0];
+            var currentMonth = recentMonths[1];
+
+            if (previousMonth.Expenses > 0)
+            {
+                var percentChange = (currentMonth.Expenses - previousMonth.Expenses) / previousMonth.Expenses * 100;
+                if (percentChange > 20)
+                {
+                    flags.Add(new AuditFlagDto
+                    {
+                        Type = "SpendingIncrease",
+                        Severity = "Warning",
+                        Message = $"Spending increased {percentChange:F0}% from {previousMonth.Month} ({previousMonth.Expenses:C}) to {currentMonth.Month} ({currentMonth.Expenses:C})",
+                        Details = new
+                        {
+                            PreviousMonth = previousMonth.Month,
+                            PreviousExpenses = previousMonth.Expenses,
+                            CurrentMonth = currentMonth.Month,
+                            CurrentExpenses = currentMonth.Expenses,
+                            PercentChange = percentChange
+                        }
+                    });
+                }
+            }
+        }
+
+        // Flag: Categories without budgets (top spending categories)
+        var topUnbudgetedCategories = response.SpendingByCategory
+            .Where(c => c.BudgetLimit == null && c.TotalSpent > 100)
+            .Take(3)
+            .ToList();
+
+        if (topUnbudgetedCategories.Any())
+        {
+            flags.Add(new AuditFlagDto
+            {
+                Type = "NoBudget",
+                Severity = "Info",
+                Message = $"Top spending categories without budgets: {string.Join(", ", topUnbudgetedCategories.Select(c => $"{c.Category} ({c.TotalSpent:C})"))}",
+                Details = topUnbudgetedCategories.Select(c => new { c.Category, c.TotalSpent }).ToList()
+            });
+        }
+
+        return flags.OrderByDescending(f => f.Severity switch
+        {
+            "Alert" => 3,
+            "Warning" => 2,
+            "Info" => 1,
+            _ => 0
+        }).ToList();
+    }
+}