Sale percentage incorrect


We currently have discounts on some of our items. Next to the price we have a percentage to show how much a customer is saving but the sale price and the percentage the customer is saving is not matching up. The sale price is correct but the percentage is not. For example, in one of our categories it shows that every item has 4% off but each saving varies depending on the product, so even if a product is 20% off it shows that its 4% off which could cause confusion to customers on how much they should be saving. Can I have some assistance of fixing this problem.