Cart abandonment and checkout drop-offs are the most critical friction points in any eCommerce funnel. Leveraging Google Analytics 4 (GA4) with Google Tag Manager (GTM), OpenCart merchants can track where users exit the funnel—enabling precise optimization and personalized remarketing.
✅ What Will You Achieve?
| GA4 Event | Purpose |
|---|---|
add_to_cart |
Detect interest but no checkout |
begin_checkout |
Detect checkout intent |
purchase |
Confirm conversion |
| Custom Dimensions | Track checkout step numbers |
| Funnel Report | Visualize drop-off rates per step |
🧰 Requirements
- OpenCart 3.x or 4.x
- Google Analytics 4 property
- GTM web container installed
- GA4 base tag implemented
- Checkout built on OpenCart’s default controller (or customized checkout endpoint)
🚀 Step-by-Step Implementation
🔹 Step 1: Track add_to_cart Events
Edit: catalog/controller/checkout/cart.php
$product_info = $this->model_catalog_product->getProduct($product_id);
$data['gtm_add_to_cart'] = json_encode([
'event' => 'add_to_cart',
'ecommerce' => [
'currency' => $this->session->data['currency'],
'value' => $product_info['price'],
'items' => [[
'item_id' => $product_info['model'],
'item_name' => $product_info['name'],
'price' => $product_info['price'],
'quantity' => $quantity
]]
]
]);
In the appropriate .twig file (e.g., cart.twig):
{% if gtm_add_to_cart %}
<script>
window.dataLayer = window.dataLayer || [];
dataLayer.push({{ gtm_add_to_cart|raw }});
</script>
{% endif %}
🔹 Step 2: Track begin_checkout Events
Edit: catalog/controller/checkout/checkout.php
$products = $this->cart->getProducts();
$items = [];
foreach ($products as $product) {
$items[] = [
'item_id' => $product['model'],
'item_name' => $product['name'],
'price' => $product['price'],
'quantity' => $product['quantity']
];
}
$data['gtm_begin_checkout'] = json_encode([
'event' => 'begin_checkout',
'ecommerce' => [
'currency' => $this->session->data['currency'],
'items' => $items
]
]);
In checkout.twig:
{% if gtm_begin_checkout %}
<script>
dataLayer.push({{ gtm_begin_checkout|raw }});
</script>
{% endif %}
🔹 Step 3: Track purchase on Order Success
Edit: catalog/controller/checkout/success.php
$order_info = $this->model_checkout_order->getOrder($this->session->data['order_id']);
$products = $this->model_checkout_order->getOrderProducts($order_info['order_id']);
$items = [];
foreach ($products as $product) {
$items[] = [
'item_id' => $product['model'],
'item_name' => $product['name'],
'price' => $product['price'],
'quantity' => $product['quantity']
];
}
$data['gtm_purchase'] = json_encode([
'event' => 'purchase',
'ecommerce' => [
'transaction_id' => $order_info['order_id'],
'value' => $order_info['total'],
'currency' => $order_info['currency_code'],
'items' => $items
]
]);
In success.twig:
{% if gtm_purchase %}
<script>
dataLayer.push({{ gtm_purchase|raw }});
</script>
{% endif %}
🔹 Step 4: Add Checkout Step Tracking (Optional but Recommended)
You can push the checkout step as a custom dimension:
$data['gtm_checkout_step'] = json_encode([
'event' => 'checkout_progress',
'ecommerce' => [
'checkout_step' => 2 // billing step
]
]);
Then in GTM, create a Custom Dimension in GA4 config:
- Name:
checkout_step - Scope: Event
🔹 Step 5: Configure GA4 Event Tags in GTM
In GTM:
- Tag Type: GA4 Event
- Use Event Name matching
add_to_cart,begin_checkout, etc. - Event Parameters:
currency,value,items
- Trigger:
- Custom Event Trigger with matching name (e.g.,
add_to_cart)
- Custom Event Trigger with matching name (e.g.,
Repeat for each event.
🔹 Step 6: Mark Conversions in GA4
In GA4 Admin → Events:
- Mark
purchaseas a conversion - Optionally also mark
begin_checkoutfor checkout funnel analysis
🔹 Step 7: Build a Funnel Exploration in GA4
Go to GA4 → Explore > Funnel Exploration
Funnel Steps:
add_to_cartbegin_checkoutpurchase
Use elapsed time to see conversion delays.
Breakdowns:
- Device
- Source/medium
- Region
- Product category
🔹 Step 8: Detect Cart Abandonment (via Audience)
In GA4 → Configure → Audiences:
- Include users who triggered
add_to_cart - AND did not trigger
begin_checkoutorpurchasein 1 hour - Use this audience for remarketing in Google Ads
🧠 Pro Tips
| Tip | Reason |
|---|---|
Match item_id with feed id |
Enables Google Ads dynamic remarketing |
| Add checkout step custom dimension | Enables more granular funnel steps |
| Use DebugView extensively | Avoid silent data errors |
| Track quantity and price for cart value | Useful for abandoned cart revenue estimation |
| Use time-based audiences | Retarget based on cart delay (e.g., 30 mins) |
🧪 QA Checklist
| Event | DataLayer Push | GTM Event Trigger | GA4 DebugView |
|---|---|---|---|
add_to_cart |
✅ | ✅ | ✅ |
begin_checkout |
✅ | ✅ | ✅ |
purchase |
✅ | ✅ | ✅ |
checkout_step |
✅ (optional) | ✅ | ✅ |
| GA4 Conversions | Tracked | Triggered | Verified |
📦 Summary Table
| Page | GA4 Event | Purpose |
|---|---|---|
| Product Page | add_to_cart |
User intent |
| Checkout Page | begin_checkout |
Purchase intent |
| Thank You Page | purchase |
Final conversion |
| Intermediate Step | checkout_progress |
Step drop-off |