Authors whose non-Kindle Unlimited books fall into the 70% royalty range are charged a delivery charge based on a MOBI’s size for sales of Kindle books on Amazon. The charge is 15¢ per megabyte (MB). The actual cover of the book is not included in calculating the size for purposes of the delivery fee.
Because of the impact of this charge, we recently had a strategy change. In the past, we used beautiful cover images at the beginning of excerpts at the back of our author’s books. The charge was significant enough that we removed them entirely.
Interestingly, MOBIs are larger than EPUBs because they contain data for multiple Kindle configurations. The delivery charge is not based on the actual file size. For example, if the book is 6 MB, you are not charged 90¢. The formula appears to be divided by 6. So a 6 MB book divided by 6 is 1 MB. This size book would have a delivery charge of 15¢. So our goal was to make the books under 6 MB so that the actual Amazon converted size is less than 1 MB. The smaller the better, when it came to saving our royalties. And our deletions worked.
Useful info to know…
~ Bobbye, SkipJack Publishing Assistant
Bobbye Marrs is a supermom extraordinaire with currently 5 jobs, 4 teenagers, 2 dogs, and a husband crazy enough to be a pastor. When she’s not working or 
learning some new hobby like the HAM radio, she is trying to be a romantic mystery writer. Look for her book, I Am My Beloved’s to debut this spring. In the meantime, she started a t-shirt business to support her writing habit at www.greetingsfrommarrs.com.