Amazon is the most powerful online retailer in the world. Although books are just part of their business model, they dominant the literary sector. Around 70% of e-book sales in the United States happen on Amazon.com. Every title in the store has a “Best Sellers Rank” (also called Sales Rank) reflecting how well it’s selling relative to the millions of books in the Amazon store.
Few things are more obsessed-over by modern authors than Amazon Best Sellers Rank. For most of us, it’s a form of numerical torture, updated hourly. Although the precise inner workings of the algorithm are known only to Amazon, there are a few general accepted principles:
- The more a book sells, the higher (closer to 1) its rank goes.
- Rankings change rapidly, often moving thousands of positions within hours.
- Paid and free books are ranked separately.
Beyond these basic principles, there is little certainty. The basic formula for Amazon Bestseller Rank seems to be sales over time, meaning that a book must continue to sell to maintain a high position on the lists. In theory, it might therefore be possible to achieve a high ranking if a book sold a modest number of copies in a short amount of time. I decided to test that theory with an experiment.
My Amazon Sales Rank Experiment
To assess the impact of rapid sales in a short time frame, I organized a coordinated buy of The Rogue Retrieval on May 12, 2016. Importantly, I didn’t make any purchases myself, for two reasons:
- I’d already bought the e-book for both of my Kindles, so Amazon wouldn’t let me.
- I didn’t want to appear to be gaming the system, or “buying the bestseller list” as is common practice in the business nonfiction world.
Instead, I turned to friends and fans, most of them fellow authors, who were willing to help. More than 50 people stepped up, and agreed to purchase the Kindle e-book at a specified time on that day. We targeted 8:00 a.m., which meant that some who live overseas bought at around midnight, NYC time (morning for them).
Here are some questions that I hoped to answer:
- How long does it take for Sales Rank to reflect new sales?
- What rank could be reached with 50+ sales in a single day?
- What’s the effect on subcategory rankings?
The Lag Time Between Sales and Ranking
There’s a lag time between book sales and the resulting change in Amazon Best Seller Rank. In other words, a purchase on Amazon doesn’t immediately boost a book’s rankings. How long does it take? The first twenty-four hours into my experiment offered some insights:
The first boost (2 hours) came from sales the day before, when some eager volunteers pulled the trigger a bit early. The two main peaks occur at hour 7 (European volunteers) and hour 16 (US volunteers). Thus, the lag isn’t quite 12 hours as I previously believed, but closer to 8 hours.
The Effect of Sales on Best Seller Rank
In total, about 57 people bought The Rogue Retrieval within a 24-hour period. Although we targeted 8 a.m., sales continued throughout the day. The rank peaked about noon the following day at 4,748 in the Paid Kindle Store:
It might surprise some that so many sales only propelled my book to #5,000, but this speaks to the size of the Amazon bookstore. If we assume it ranks 1 million books (an underestimate), this ranking is in the top 0.5%.
Notice another property of Amazon Sales Rank: increases happen quickly (as “jumps”), whereas the post-sale decrease in rank happens more slowly. Especially for the first couple of days. After 72 hours, however, the drop-off becomes more precipitous. This seems to support something I’ve read about Amazon’s internal ranking algorithm: sales from previous days carry some weight. The window seems to be 48-72 hours.
Subcategory Rankings on Amazon
Book subcategories are a vital element of the Amazon store. For readers, they provide a means to browse the bestsellers in a favorite genre or subgenre. For authors, the rankings provide discoverability, especially in the top 100 (which can readily be browsed). The top 10-20 get an even bigger boost, as these titles show up on the first page. Thus, I watched the category ranks as well:
My book happens to be in three major categories, two of which seem redundant (Time Travel Books and Time Travel Kindle eBooks). The third category is Technothrillers, which is far more competitive. Look at this scatterplot of category rank by overall Kindle Sales Rank:
At its peak (4,748 in the Kindle store), The Rogue Retrieval reached:
- #24 in Time Travel Books
- #29 in Time Travel Kindle eBooks
- #50 in Technothrillers
Thus, even though the two Time Travel categories seem redundant (and arguably not appropriate for my book, but that’s another story), the non-Kindle category offers a competitive advantage. Presumably, that’s because five other books were selling better, but are only available as e-books.
I’m disappointed, but not entirely surprised, not to have reached a higher ranking in Technothrillers. It’s a supremely competitive category dominated (currently) by the likes of A.G. Riddle. My book might arguably be categorized as Epic Fantasy instead, but that’s even more cutthroat in the Amazon store.
Bottom line, I hit the top 50 in all three subcategories and top 30 in two of them. Although I’m happy to have gained a bit of discoverability, I won’t be making any bestseller claims in my Twitter profile.
Long-term Effects of Sales Rank
Perhaps the most surprising property of Amazon Best Seller Rank is how much it changes over time. Look at the rank for The Rogue Retrieval for the entire month of May:
The huge peak from my sales-spike experiment is obvious, and does seem to have a tailing effect. However, just four days after that massive spike, my book returns to baseline (around 100k). Amazon Best Seller Rank is a dynamic and fickle beast.
Conclusions on Amazon Rank
This experiment uncovered some interesting properties of Amazon Best Seller Rank:
- The lag time between sales and ranking is around 8 hours.
- The Sales Rank benefit from a major spike carries over 1-2 days.
- 50 sales in a single day can propel a book to #5,000 in the Kindle Store.
- It’s possible to reach good category ranks (top 30) with such a strategy.
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