I'll tell you which of your books to push, which to fix, and which to stop paying for.

Plenty of numbers. No next move.

Book Report, Publisher Champ, PublishWide are good tools. Keep using them. They'll show you sales, page reads, sometimes ad spend.

But a chart isn't a decision. Here's the question none of them answer:

It usually shows up one of three ways:

• Facebook's dashboard and your KDP reports tell two different stories, and neither one counts the readers who saw the ad and bought without ever clicking it. If attribution isn't set up properly, you're guessing.
• You keep spending on a series where readers quit after book one, and calling it a traffic problem when it's a book-two problem.
• Nobody's made the call on the backlist. Which titles to push, which to fix, which to stop feeding.

Underneath most of it is read-through, meaning how many book-one readers carry on to book two. Around 50 to 60% on paid sales is healthy (Kindlepreneur; Authors Game). Well under that, and the fix is the books, not more ad spend.

Read-through matters because of what it does to the second of the two numbers below, which is the one that decides whether you can afford to grow at all.

Most people can quote their read-through rate. Almost nobody has a monthly habit of acting on it. That habit is what I'm selling.

The two numbers everything comes down to

When you're deciding where the money goes, there are really only two numbers.

What it costs to get one new reader. Not a click. Not an impression. A person who bought something of yours for the first time.

What that reader is worth once you've got them. Not what they spent on the first book. What they spend across everything they go on to read.

I've published the full breakdown of how I calculate both numbers, formulas and worked example included.

If the second number is comfortably bigger than the first, you can spend more and grow. If it isn't, every ad dollar makes the hole deeper, and better targeting won't save it.

Almost everyone works on the cost side. Better creative, tighter targeting, cheaper clicks. That's real work, and it has a floor, because there's only so cheap a reader can get.

The value side has no ceiling, and almost nobody works on it. It goes up when readers finish book one and start book two. It goes up when a series is priced so the whole run makes sense rather than just the first book. It goes up when the box set exists, when the reading order is obvious, when a dead series stops eating the promo slot a live one should have.

And it's a number about everything you're selling at once, not about any one book. Forty titles means a reader has forty chances to be worth something. That's the advantage you have over an author with four books, and most presses never collect on it.

Get those two numbers far enough apart in your favour and you can outbid anyone for the same reader and still make money. That's the whole game.

Here's the near-term version. Say you're putting $3,000 a month into ads across fifteen titles, and a third of it is feeding a series where readers quit after book one. That's $1,000 a month walking out the door, and it keeps walking until somebody looks. Most of the time the first thing I find pays for the check several times over. Sometimes everything's running tight, in which case I'll say so and you'll have spent a small amount to stop wondering.