diff --git a/MoneyMap/Pages/Receipts.cshtml b/MoneyMap/Pages/Receipts.cshtml
index 02f1fa2..f4bc2e3 100644
--- a/MoneyMap/Pages/Receipts.cshtml
+++ b/MoneyMap/Pages/Receipts.cshtml
@@ -18,6 +18,39 @@
     </div>
 }
 
+<!-- Duplicate Warnings -->
+@if (Model.DuplicateWarnings.Any())
+{
+    <div class="alert alert-warning alert-dismissible fade show" role="alert">
+        <h5 class="alert-heading">⚠️ Potential Duplicates Detected</h5>
+        <p>The following receipt(s) may be duplicates of the one you just uploaded:</p>
+        <ul class="mb-0">
+            @foreach (var warning in Model.DuplicateWarnings)
+            {
+                <li>
+                    <strong>Receipt #@warning.ReceiptId</strong> - @warning.FileName
+                    <br />
+                    <small class="text-muted">
+                        Uploaded: @warning.UploadedAtUtc.ToLocalTime().ToString("yyyy-MM-dd HH:mm") |
+                        Reason: @warning.Reason
+                        @if (warning.TransactionId.HasValue)
+                        {
+                            <span> | Mapped to: @warning.TransactionName (Transaction #@warning.TransactionId)</span>
+                        }
+                        else
+                        {
+                            <span> | Status: Unmapped</span>
+                        }
+                    </small>
+                    <br />
+                    <a asp-page="/ViewReceipt" asp-route-id="@warning.ReceiptId" class="btn btn-sm btn-outline-primary mt-1">View Receipt #@warning.ReceiptId</a>
+                </li>
+            }
+        </ul>
+        <button type="button" class="btn-close" data-bs-dismiss="alert" aria-label="Close"></button>
+    </div>
+}
+
 <!-- Upload Section -->
 <div class="card shadow-sm mb-3">
     <div class="card-header">
diff --git a/MoneyMap/Pages/Receipts.cshtml.cs b/MoneyMap/Pages/Receipts.cshtml.cs
index 4bb81cc..b634a6b 100644
--- a/MoneyMap/Pages/Receipts.cshtml.cs
+++ b/MoneyMap/Pages/Receipts.cshtml.cs
@@ -29,9 +29,20 @@ namespace MoneyMap.Pages
         [TempData]
         public bool IsSuccess { get; set; }
 
+        [TempData]
+        public string? DuplicateWarningsJson { get; set; }
+
+        public List<DuplicateWarning> DuplicateWarnings { get; set; } = new();
+
         public async Task OnGetAsync()
         {
             await LoadReceiptsAsync();
+
+            // Deserialize duplicate warnings if present
+            if (!string.IsNullOrWhiteSpace(DuplicateWarningsJson))
+            {
+                DuplicateWarnings = System.Text.Json.JsonSerializer.Deserialize<List<DuplicateWarning>>(DuplicateWarningsJson) ?? new();
+            }
         }
 
         public async Task<IActionResult> OnPostUploadAsync()
@@ -48,8 +59,17 @@ namespace MoneyMap.Pages
 
             if (result.IsSuccess)
             {
-                Message = "Receipt uploaded successfully!";
-                IsSuccess = true;
+                if (result.DuplicateWarnings.Any())
+                {
+                    Message = $"Receipt uploaded successfully, but {result.DuplicateWarnings.Count} potential duplicate(s) detected.";
+                    IsSuccess = true;
+                    DuplicateWarningsJson = System.Text.Json.JsonSerializer.Serialize(result.DuplicateWarnings);
+                }
+                else
+                {
+                    Message = "Receipt uploaded successfully!";
+                    IsSuccess = true;
+                }
                 return RedirectToPage();
             }
             else
diff --git a/MoneyMap/Services/ReceiptManager.cs b/MoneyMap/Services/ReceiptManager.cs
index 73d0c7b..dd8605a 100644
--- a/MoneyMap/Services/ReceiptManager.cs
+++ b/MoneyMap/Services/ReceiptManager.cs
@@ -86,7 +86,7 @@ namespace MoneyMap.Services
                 fileHash = BitConverter.ToString(hashBytes).Replace("-", "").ToLowerInvariant();
             }
 
-            // Check for duplicate (same transaction + same hash, or same hash if unmapped)
+            // Check for exact duplicate (same transaction + same hash)
             if (transactionId.HasValue)
             {
                 var existingReceipt = await _db.Receipts
@@ -96,6 +96,9 @@ namespace MoneyMap.Services
                     return ReceiptUploadResult.Failure("This receipt has already been uploaded for this transaction.");
             }
 
+            // Check for potential duplicates (same hash, same name+size)
+            var duplicateWarnings = await CheckForDuplicatesAsync(fileHash, file.FileName, file.Length);
+
             // Generate unique filename
             var storedFileName = $"{transactionId?.ToString() ?? "unmapped"}_{Guid.NewGuid()}{extension}";
             var filePath = Path.Combine(receiptsBasePath, storedFileName);
@@ -125,7 +128,55 @@ namespace MoneyMap.Services
             _db.Receipts.Add(receipt);
             await _db.SaveChangesAsync();
 
-            return ReceiptUploadResult.Success(receipt);
+            return ReceiptUploadResult.Success(receipt, duplicateWarnings);
+        }
+
+        private async Task<List<DuplicateWarning>> CheckForDuplicatesAsync(string fileHash, string fileName, long fileSize)
+        {
+            var warnings = new List<DuplicateWarning>();
+
+            // Check for receipts with same hash
+            var hashMatches = await _db.Receipts
+                .Include(r => r.Transaction)
+                .Where(r => r.FileHashSha256 == fileHash)
+                .ToListAsync();
+
+            foreach (var match in hashMatches)
+            {
+                warnings.Add(new DuplicateWarning
+                {
+                    ReceiptId = match.Id,
+                    FileName = match.FileName,
+                    UploadedAtUtc = match.UploadedAtUtc,
+                    TransactionId = match.TransactionId,
+                    TransactionName = match.Transaction?.Name,
+                    Reason = "Identical file content (same hash)"
+                });
+            }
+
+            // Check for receipts with same name and size (but different hash - might be resaved/edited)
+            if (!warnings.Any())
+            {
+                var nameAndSizeMatches = await _db.Receipts
+                    .Include(r => r.Transaction)
+                    .Where(r => r.FileName == fileName && r.FileSizeBytes == fileSize)
+                    .ToListAsync();
+
+                foreach (var match in nameAndSizeMatches)
+                {
+                    warnings.Add(new DuplicateWarning
+                    {
+                        ReceiptId = match.Id,
+                        FileName = match.FileName,
+                        UploadedAtUtc = match.UploadedAtUtc,
+                        TransactionId = match.TransactionId,
+                        TransactionName = match.Transaction?.Name,
+                        Reason = "Same file name and size"
+                    });
+                }
+            }
+
+            return warnings;
         }
 
         public async Task<bool> MapReceiptToTransactionAsync(long receiptId, long transactionId)
@@ -227,11 +278,22 @@ namespace MoneyMap.Services
         public bool IsSuccess { get; init; }
         public Receipt? Receipt { get; init; }
         public string? ErrorMessage { get; init; }
+        public List<DuplicateWarning> DuplicateWarnings { get; init; } = new();
 
-        public static ReceiptUploadResult Success(Receipt receipt) =>
-            new() { IsSuccess = true, Receipt = receipt };
+        public static ReceiptUploadResult Success(Receipt receipt, List<DuplicateWarning>? warnings = null) =>
+            new() { IsSuccess = true, Receipt = receipt, DuplicateWarnings = warnings ?? new() };
 
         public static ReceiptUploadResult Failure(string error) =>
             new() { IsSuccess = false, ErrorMessage = error };
     }
+
+    public class DuplicateWarning
+    {
+        public long ReceiptId { get; set; }
+        public string FileName { get; set; } = "";
+        public DateTime UploadedAtUtc { get; set; }
+        public long? TransactionId { get; set; }
+        public string? TransactionName { get; set; }
+        public string Reason { get; set; } = "";
+    }
 }
\ No newline at end of file