Yes, there is a lot of "Well, it depends," when answering this question.
But that answer is such a letdown. Our goal here is to provide an answer that is practical, helpful, and as much one-size-fits-all as possible given all the different variables.
Most self-published books sell less than 100 copies
We wish the news was rosier than this, but it's the truth. And the road to 100 books sold isn't easy. What tends to happen:
1 - 25 book sales - Author posts on social media a couple of times, sends out a few emails, sells 10-20 copies to friends and family.
25 - 100 book sales - Author has an ongoing social media campaign. Already has a following on a blog or newsletter. Does a little marketing. Maybe runs a story in the local newspaper. Reaches out to people, reminds them about the book.
Selling more than 20 books isn't a given. It takes an ongoing effort and a certain level of consistent sales/marketing. This can be really tough for authors who struggle with self-promotion.
Going from 100 to 500 copies
Part of this is related to the genre. For example, a children's book will have a better shot at selling 200+ copies than a self-published historical fiction novel.
A couple of reasons for this:
Some people are already buying 5+ children's books a year. They'd rather buy from a writer/artist they know vs. whatever mainstream book is out there
People might buy multiple copies of the children's book, give them out as gifts
The other part of this 100 to 500 book jump is moving outside the friends/family/immediate network sphere. Especially when going from 200 to 500 copies, you have to start reaching people you've never actually met before.
What this next group of readers looks like:
Friend of a friend (of a friend)
Someone in your city/town supporting a local author
Or supporting an author from their home state
Someone who heard about it on the radio
Read an article in the newspaper/magazine
This stage of the process (going from 250 to 500 sales) is where it becomes important to get into bookstores or other retailers. You want to be in front of active readers, expanding your potential audience.
Going from 500 to 1,000 copies
The process to become traditionally published is a very, very, long road, but the payoff is felt at this stage. Traditional publishers have connections to bookstores all around the country. They've been here before. Know how to promote a book and push beyond the 500 copies sold threshold. They also have a vested interest in seeing your book do well.
It's not impossible for a self-published author to climb to this tier, but it's very difficult. It will likely take 2-3 years of consistent effort.
Long story short: Traditionally published authors spend longer getting their book out into the world compared to self-published authors, but less time going from 100 to 500 and definitely a higher percentage of reaching 1,000 copies sold.
Long Overdue Books: How self-publishing should work alongside traditional publishing
When it comes to traditional publishing, the model has always been for authors to send their manuscripts to literary agents. The agents then decide whether or not the manuscript makes it through to a publisher. The agents' criteria is a mixture of judging the book's quality and predicting if the book could sell 500+ copies.
But here's what we've been wondering at Long Overdue Books: Does self-publishing actually work better as the proving grounds? And isn't it a better experience for both the author's experience and the publisher's goal of accurately predicting sales numbers?
Here's what we mean. Self-publishing gives the author a chance to get their book out there. And since all the self-publishing tools continue to improve (sites like Amazon, BookBaby, PrintNinja, Pint Size Productions, etc.) we're seeing higher quality for self-published books. Also, if the author has the financial means, they can work with professional editors, artists, continuing to improve their book. With the help of LinkedIn, it's a lot easier to find and reach out to the pros.
On the business side, once the book's out there, an author can report real sales numbers to the traditional publishers. Hey, my book's been out for 4 months, I've sold 125 copies. Here's a physical copy of my book for your consideration. Doesn't that just feel better than attaching a Word document to an email?
The traditional publishers would become like a publishing version of Shark Tank. They're not making as big of a guess anymore. They have actual sales data. They're deciding if they can take the book from 125 copies sold to 12,500. It's like what we're seeing with the site Wattpad, traditional publishers, and even Netflix, are now greenlighting stories that have a growing audience on the site.
In our opinion, there isn't this big dramatic choice of, "Should I self-publish or traditionally publish?" The two should work hand-in-hand.
But we can't stress these next two points enough
If you're self-publishing, build your budget around a reality where the book might only make $300 - $500 in sales (100 sales at $3-5 royalties per book). This doesn't mean give up on the dream of selling thousands or millions of copies. Absolutely not. But don't use that as your model for running the math (meaning: Hey, I'll spend $10,000 because I know I'll make it back when this becomes a bestseller).
Build a budget you're comfortable with. If you can put $3 - $5k+ into a book and it doesn't matter if you make it back, that's great. But if you can only put a couple of hundred dollars into it, that's alright too. You can always come back and make a second or third edition later. Your book doesn't have an expiration date.
And second, I would view editing and book design dollars as marketing dollars. You're much better off putting $1,000 into book design/cover design or professional editing than you are putting $1,000 into Facebook/Instagram ads, Google ad words, or other forms of advertising. Those first book sale milestones, going from 20 to 100, 100 to 250, 250 to 500, this relies heavily on word of mouth.
And the best way to build word of mouth is by making your book the best it can possibly be.