It should be calculated individually for each product, but remember that the bigger a discount you give, the bigger the churn rate will be. Also, too-generous discounts can affect the perceived value of goods. You should always weigh all the pros and cons before launching a promotional campaign. A 10-20% price reduction puts you in manageable risk, while 50% discounts or “2 for 1” offers may cause a very serious impact on your revenue.