--
title: "How I Decide Whether a 39-Hour Audiobook Is Worth an Audible Credit"
description: "A credit-value framework for long audiobooks, using The Running Grave (Robert Galbraith) as a case study: runtime, price, narration, and the per-hour math."
tags: ["audiobooks", "audible", "book-review"]
canonical_url: https://getcreditworth.com/blog/the-running-grave-audiobook-review
Most people treat an Audible credit like a flat token: one credit, one book, done. But credits aren't equal because the books aren't equal. A credit spent on a 6-hour novella and a credit spent on a 39-hour doorstop buy you wildly different amounts of listening. The real question isn't "is this book good?" — it's "how much audio am I getting per credit?"
I built a small habit around this. Before I spend a credit I run three numbers: runtime in hours, cash price, and star rating weighted by review count. The formula is crude but useful:
value ≈ (hours × rating) / cash price
A book that's $35 and 39 hours scores higher than a $30 book that's 9 hours. That's the whole game.
One wrinkle people miss: the rating should be weighted by review count. A 5-star book with 40 reviews is noise; a 4.5-star book with 18,000 reviews is signal. I cap the rating at 4.5 for anything under a few thousand reviews, because the early ratings on a new release are often friends and fans. The Running Grave has the volume, so its score holds.
Take The Running Grave, Robert Galbraith's seventh Cormoran Strike novel. It runs close to 39 hours on audio and sells for $34.99, or one credit. Run the numbers: 39 × 4.5 ÷ 34.99 ≈ 5.0. Not the highest score in the catalog, but squarely in the "use a credit, don't pay cash" zone. The credit is fixed-value, so you want the most expensive, longest book you'll actually finish. The Running Grave qualifies on both counts.
The catch is fit. Galbraith writes slow, dense, character-driven crime. If you need a plot that moves every five minutes, 39 hours will feel like a marathon. But if you commute daily or listen while doing dishes, this is exactly the kind of book a credit was made for.
There's also a cash-versus-credit trap. If a title costs less than your monthly fee (about $14.95 on the common plan), paying cash and saving the credit is usually smarter, because the credit's effective floor is that fee. The Running Grave at $34.99 clears that bar easily, which is another reason the credit wins. Where people waste credits is spending them on $9 shorts they could have bought outright.
None of this matters if you won't finish the book. A credit spent on a 39-hour title you abandon in hour 10 is worse than a credit spent on a tight 8-hour thriller you loved. I only reach for the long ones when I know the author's rhythm fits my listening life. Galbraith does; that's why this one landed.
Narration matters too. Robert Glenister has read the whole series, and that continuity is worth something. Strike gets a tired, careful voice; Robin stays precise. The cult members in this one let him show range without slipping into caricature.
My rule of thumb after doing this for a while: use a credit on anything over ~20 hours or over $20 cash. Pay cash for short, cheap titles and save the credit for the big ones. The Running Grave is a textbook "spend the credit" pick.
Full breakdown with the value table is on getcreditworth.com: https://getcreditworth.com/blog/the-running-grave-audiobook-review
