Introduction

WooCommerce Subscriptions is a powerful tool for recurring billing, but many SaaS-like businesses and membership sites need usage-based billing or prorated subscription charges.

In this guide, we’ll cover how to track subscription usage, calculate prorated amounts, and automate billing adjustments inside WooCommerce.

Why Usage Tracking & Prorated Billing Matter

• Fair billing: Charge customers based on actual usage.
• Seamless plan changes: Automatically handle mid-cycle upgrades/downgrades.
• SaaS-like flexibility: Offer metered or pay-as-you-go billing in WooCommerce.
• Improved retention: Transparent pricing builds customer trust.

Tools & Requirements

• WooCommerce Subscriptions
• WooCommerce (latest version)
• PHP knowledge (custom hooks & filters)
• Optional: Action Scheduler (for automated billing tasks)

Step 1: Track Subscription Usage

Create a custom meta field to track usage per subscription.

function bookwp_add_usage_meta($subscription) {
    if (!$subscription->get_meta('usage')) {
        $subscription->update_meta_data('usage', 0);
        $subscription->save();
    }
}
add_action('woocommerce_subscription_created', 'bookwp_add_usage_meta');

Now you can update usage whenever an event occurs (e.g., API call, user action).

function bookwp_update_usage($subscription_id, $units) {
    $subscription = wcs_get_subscription($subscription_id);
    $usage = (int) $subscription->get_meta('usage');
    $subscription->update_meta_data('usage', $usage + $units);
    $subscription->save();
}

Step 2: Calculate Prorated Billing

If a customer upgrades or downgrades mid-cycle, prorate their next payment.

function bookwp_prorate_amount($subscription) {
    $next_payment = $subscription->get_time('next_payment');
    $start = $subscription->get_time('last_payment');
    $days_in_cycle = ($next_payment - $start) / DAY_IN_SECONDS;
    $days_remaining = ($next_payment - time()) / DAY_IN_SECONDS;

    $plan_price = $subscription->get_total();
    return round(($plan_price / $days_in_cycle) * $days_remaining, 2);
}

You can apply this during a subscription switch to charge only the prorated difference.

Step 3: Automate Billing Adjustments

Hook into woocommerce_scheduled_subscription_payment to adjust charges:

add_action('woocommerce_scheduled_subscription_payment', 'bookwp_adjust_subscription_payment', 10, 2);

function bookwp_adjust_subscription_payment($amount, $subscription) {
    $usage = (int) $subscription->get_meta('usage');
    $rate_per_unit = 0.50; // Example rate
    $extra_charges = $usage * $rate_per_unit;

    return $amount + $extra_charges;
}

Step 4: Display Usage in My Account

Show customers their current usage:

add_action('woocommerce_subscription_details_table_after', function($subscription) {
    $usage = $subscription->get_meta('usage') ?: 0;
    echo "<p><strong>Usage this cycle:</strong> {$usage} units</p>";
});

Advanced Enhancements

• Webhook integration: Track usage automatically from an external service (e.g., SaaS API).
• Partial refunds: Automatically refund unused subscription time for downgrades.
• Custom admin UI: Add a usage editor in the admin subscription screen.
• Reports: Generate usage-based revenue analytics for admin dashboards.

Best Practices

• Always log usage updates for audit purposes.
• Validate usage inputs to prevent incorrect billing.
• Provide clear breakdowns of charges to customers.
• Test on a staging site before going live.