While customizing the product tile JS template (https://tagalys.freshdesk.com/support/solutions/articles/26000027566-how-do-i-add-custom-attributes-to-product-tiles-), you can calculate the discount percentage and display a label. The details required to calculate this are available in the product_details variable.


Example code:

if (product_details.sale_price != product_details.price) {

  var discount_amount = Math.round(((product_details.price - product_details.sale_price) / product_details.price) * 100);

  var $discount = $('<span class="product-discount-percentage">').html(discount_amount + '% OFF');

  $link.append($discount);

}