diff --git a/source/packages/plg_system_mokosuitefield/src/Helper/InvoiceHelper.php b/source/packages/plg_system_mokosuitefield/src/Helper/InvoiceHelper.php
new file mode 100644
index 0000000..5d976ce
--- /dev/null
+++ b/source/packages/plg_system_mokosuitefield/src/Helper/InvoiceHelper.php
@@ -0,0 +1,146 @@
+<?php
+namespace Moko\Plugin\System\MokoSuiteField\Helper;
+
+defined('_JEXEC') or die;
+
+use Joomla\CMS\Factory;
+use Joomla\Database\DatabaseInterface;
+
+/**
+ * Field service invoicing — generate invoices from completed work orders with labor + parts.
+ */
+class InvoiceHelper
+{
+	/**
+	 * Generate a CRM invoice from a completed work order.
+	 */
+	public static function generateFromWorkOrder(int $woId): int
+	{
+		$db  = Factory::getContainer()->get(DatabaseInterface::class);
+		$now = Factory::getDate()->toSql();
+
+		// Load work order
+		$db->setQuery($db->getQuery(true)
+			->select('wo.*, cd.name AS customer_name')
+			->from($db->quoteName('#__mokosuitefield_work_orders', 'wo'))
+			->join('LEFT', $db->quoteName('#__contact_details', 'cd') . ' ON cd.id = wo.contact_id')
+			->where('wo.id = ' . $woId));
+		$wo = $db->loadObject();
+
+		if (!$wo) throw new \RuntimeException('Work order not found: ' . $woId);
+
+		$params = Factory::getApplication()->getParams('com_mokosuitefield');
+		$laborRate = (float) $params->get('default_labor_rate', 85.00);
+
+		// Get time entries
+		$db->setQuery($db->getQuery(true)
+			->select('*')
+			->from('#__mokosuitefield_time_entries')
+			->where('wo_id = ' . $woId));
+		$timeEntries = $db->loadObjectList() ?: [];
+
+		$totalHours = 0;
+		foreach ($timeEntries as $te) {
+			$totalHours += (float) $te->hours;
+		}
+
+		// Get parts used
+		$db->setQuery($db->getQuery(true)
+			->select('wi.*, p.title AS part_name, p.price')
+			->from($db->quoteName('#__mokosuitefield_wo_items', 'wi'))
+			->join('LEFT', $db->quoteName('#__mokosuite_crm_products', 'p') . ' ON p.id = wi.product_id')
+			->where('wi.wo_id = ' . $woId));
+		$parts = $db->loadObjectList() ?: [];
+
+		$partsTotal = 0;
+		foreach ($parts as $part) {
+			$partsTotal += (float) ($part->price ?? 0) * (int) $part->quantity;
+		}
+
+		$laborTotal = round($totalHours * $laborRate, 2);
+		$subtotal = $laborTotal + $partsTotal;
+		$taxRate = (float) $params->get('default_tax_rate', 0.07);
+		$tax = round($subtotal * $taxRate, 2);
+		$total = $subtotal + $tax;
+
+		// Create CRM invoice
+		$seq = (int) $db->setQuery($db->getQuery(true)->select('COUNT(*)')->from('#__mokosuite_crm_invoices'))->loadResult() + 1;
+
+		$invoice = (object) [
+			'contact_id'     => $wo->contact_id,
+			'invoice_number' => 'FSI-' . date('Ymd') . '-' . str_pad($seq, 4, '0', STR_PAD_LEFT),
+			'type'           => 'standard',
+			'subtotal'       => $subtotal,
+			'tax'            => $tax,
+			'total'          => $total,
+			'balance_due'    => $total,
+			'status'         => 'draft',
+			'due_date'       => date('Y-m-d', strtotime('+30 days')),
+			'notes'          => 'Field Service Invoice for WO #' . ($wo->wo_number ?? $woId),
+			'created'        => $now,
+			'created_by'     => Factory::getApplication()->getIdentity()->id,
+		];
+		$db->insertObject('#__mokosuite_crm_invoices', $invoice, 'id');
+		$invoiceId = (int) $invoice->id;
+
+		// Add labor line item
+		if ($totalHours > 0) {
+			$db->insertObject('#__mokosuite_crm_invoice_items', (object) [
+				'invoice_id'   => $invoiceId,
+				'description'  => 'Labor — ' . number_format($totalHours, 1) . ' hours @ $' . number_format($laborRate, 2) . '/hr',
+				'quantity'     => $totalHours,
+				'unit_price'   => $laborRate,
+				'line_total'   => $laborTotal,
+			]);
+		}
+
+		// Add parts line items
+		foreach ($parts as $part) {
+			$db->insertObject('#__mokosuite_crm_invoice_items', (object) [
+				'invoice_id'   => $invoiceId,
+				'product_id'   => $part->product_id,
+				'description'  => $part->part_name ?? 'Part',
+				'quantity'     => $part->quantity,
+				'unit_price'   => $part->price ?? 0,
+				'line_total'   => round((float) ($part->price ?? 0) * (int) $part->quantity, 2),
+			]);
+		}
+
+		// Link invoice to work order
+		$db->setQuery($db->getQuery(true)
+			->update('#__mokosuitefield_work_orders')
+			->set('invoice_id = ' . $invoiceId)
+			->where('id = ' . $woId));
+		$db->execute();
+
+		return $invoiceId;
+	}
+
+	/**
+	 * Batch generate invoices for all completed, uninvoiced work orders.
+	 */
+	public static function batchGenerate(): array
+	{
+		$db = Factory::getContainer()->get(DatabaseInterface::class);
+
+		$db->setQuery($db->getQuery(true)
+			->select('id')
+			->from('#__mokosuitefield_work_orders')
+			->where($db->quoteName('status') . ' = ' . $db->quote('completed'))
+			->where('invoice_id IS NULL OR invoice_id = 0')
+			->order('completed_at ASC'));
+		$woIds = $db->loadColumn() ?: [];
+
+		$results = [];
+		foreach ($woIds as $woId) {
+			try {
+				$invoiceId = self::generateFromWorkOrder((int) $woId);
+				$results[] = ['wo_id' => $woId, 'invoice_id' => $invoiceId, 'success' => true];
+			} catch (\Throwable $e) {
+				$results[] = ['wo_id' => $woId, 'error' => $e->getMessage(), 'success' => false];
+			}
+		}
+
+		return $results;
+	}
+}