diff --git a/assets/mail/email_template_invoice.php b/assets/mail/email_template_invoice.php
index 4b1a2b8..8e936c9 100644
--- a/assets/mail/email_template_invoice.php
+++ b/assets/mail/email_template_invoice.php
@@ -1,5 +1,6 @@
 <?php
 $payment_method = 'payment_method_'.$invoice_data['header']['payment_method'];
+$invoice_identifcation_number = date('ymd', strtotime($invoice_date)) . '-' . $invoice_data['header']['id'];
 
 $message = '
 <!DOCTYPE html>
@@ -50,7 +51,7 @@ $message = '
                                             </tr>
                                             <tr>
                                                 <td style="padding: 3px 0;"><strong>Invoice Number:</strong></td>
-                                                <td style="padding: 3px 0;">' . htmlspecialchars($order_id) . '</td>
+                                                <td style="padding: 3px 0;">' . htmlspecialchars($invoice_identifcation_number) . '</td>
                                             </tr>
                                             <tr>
                                                 <td style="padding: 3px 0;"><strong>Your Vat Number:</strong></td>
diff --git a/assets/mail/pdf_template_invoice.php b/assets/mail/pdf_template_invoice.php
index afad03f..cf99e04 100644
--- a/assets/mail/pdf_template_invoice.php
+++ b/assets/mail/pdf_template_invoice.php
@@ -1,5 +1,6 @@
 <?php
 $payment_method = 'payment_method_'.$invoice_data['header']['payment_method'];
+$invoice_identifcation_number = date('ymd', strtotime($invoice_date)) . '-' . $invoice_data['header']['id'];
 
 $pdf = '<!DOCTYPE html>
 <html lang="' . strtolower($language) . '">
@@ -232,7 +233,7 @@ $pdf = '<!DOCTYPE html>
             </div>
             <div class="detail-row">
                 <div class="detail-label">Invoice Number</div>
-                <div class="detail-value">: ' . htmlspecialchars($order_id) . '</div>
+                <div class="detail-value">: ' . htmlspecialchars($invoice_identifcation_number) . '</div>
             </div>
             <div class="detail-row">
                 <div class="detail-label">Your Vat Number</div>
