That’s correct. (but it should be earnings with author fee, not without 
)
There is a simpler way to calculate your earnings. You don’t really need to bother yourself about the buyer fee. Simply look at the price you type when you submit your item, if you’re a non-exclusive author you’ll earn 45% of that number. And if you’re exclusive you’ll earn 62.5%-87.5%.
Or you can use this tool: http://www.enableds.com/items/tool/ 