Free shipping calculator for cart and checkout

add_action( 'woocommerce_before_cart', function() {

	do_action( 'ccom_free_shipping_calc' );

} );

add_action( 'woocommerce_before_checkout_form', function() {

	do_action( 'ccom_free_shipping_calc' );

} );

add_action( 'ccom_free_shipping_calc', function() {

	// Get Subtotal
	$subtotal = WC()->cart->get_subtotal();

	// Handle Free Shipping Threshold Reached
	if( $subtotal >= 50 ) {
		return;
	}

	// Calculate Remainder
	$remaining = 50 - $subtotal;

	// Output Message
	printf(
		'<div class="woocommerce-error"><strong>%s</strong></div>',
		wc_price( $remaining )
			. ' remaining to get free shipping on this order'
	);

} );