So what I have here is a code snippet to calculate individual product discount and display it in sale bubble. Replace all the codes in following files your theme folder/woocommerce/loop/sale-flash.php and your theme folder/woocommerce/single-product/sale-flash.php with below code.
If the files are not present, load them from the Woocommerce template dir.
Thats it you just added a cool feature which has potential to increase your sales.
Good thing about this code is even if your product is variant type (multiple type of single product) and has different percentage of offers for different variants then this code will take the best percentage out of the all variants and displays it. For example you have 3 product variant each has three different percentage 3%,4%,1% then it will display 4% in sales bubble.
Isn’t that cool ? Go on now.