Commerce: Show quantity discounts
What have you tried so far?

The documentation seems to be missing, but looking at /craft/plugins/commerce/models/Commerce_DiscountModel.php you can find the properties purchaseQty and perItemDiscount that you need for the calculations.

{% for prod in product.variants %}
   {% for discount in craft.commerce.discounts %}
      {% set totalPrice = (discount.purchaseQty * prod.price) %}
      {% set totalDiscountPrice = (discount.purchaseQty * (prod.price + discount.perItemDiscount)) %}
      {% set totalDiscount = (totalPrice-totalDiscountPrice) %}
      {% set totalDiscountPercent = (totalDiscount/totalPrice)*100 %}

      &lt;p&gt;If you buy {{ discount.purchaseQty }} items, you only pay {{ totalDiscountPrice|currency(cart.currency) }} instead of {{ prod.price|currency(cart.currency) }} per item. So your total today is only {{ totalDiscountPrice|currency(cart.currency) }} insted of {{ totalPrice|currency(cart.currency) }}. You therefore save {{ totalDiscount|currency(cart.currency) }}. That's a discount of {{ totalDiscountPercent|round }}%.&lt;/p&gt;
   {% endfor %}
{% endfor %}


This will show all of the discounts for all of the products. You will need to modify it slightly if you have specified the discount for a specific product. You also need to check if the discount is enabled or not using discount.enabled