As a general rule of thumb, lightning deals are usually a 10% discount off the regular Amazon price.
40% off "List Price"
Well, my point is don't look at the "List Price", look at pre deal price on Amazon. And you don't often see 40% off the "List Price" for a lightning deal, they usually only hit that discount level for deals of the day or special days like Prime day or Black Friday. The 10% rule isn't perfect, but it's a good expectation to have. You will occasionally be pleasantly surprised with a 20% discount, but more often than not you will get what you expected.