Your ACoS is 22%. Is that good?
Honestly, there's no way to tell. Not from that number alone. We've seen accounts at 22% ACoS compounding beautifully and accounts at 22% ACoS quietly dying, and the dashboard looked identical in both. That's the problem with the way most brands judge their advertising: the metric they stare at hardest is the one least capable of answering the question they're actually asking.
The ACoS vs TACoS distinction sounds like jargon, but underneath it sits the difference between measuring your ads and measuring your business.
ACoS vs TACoS starts with what ACoS leaves out
ACoS is ad spend divided by ad-attributed revenue. Spend £1,000, get £4,000 of sales tracked to those ads, and your ACoS is 25%. Simple, and useful as far as it goes.
Here's what it leaves out: every sale your ads helped create but didn't get credited for. On Amazon, advertising doesn't just win the orders in its own attribution window. Paid sales feed your best-seller rank, your rank feeds your organic position and your organic position feeds sales that never touch a campaign report. The whole point of spending on Amazon is that flywheel.
ACoS is blind to it by design. Judge your advertising on ACoS alone and you're grading the engine while ignoring whether the car moved.
TACoS includes the part that pays your bills
TACoS, total advertising cost of sale, is ad spend divided by total revenue. Paid and organic together.
Watch it over months and it tells you something ACoS never can. If your TACoS is falling while spend holds steady, your organic business is growing underneath the ads, which is exactly what you want. The advertising is building an asset. If your TACoS is flat or rising, you're renting your sales. Turn the ads off and the revenue goes with them.
Two brands, both at 25% ACoS. One has a TACoS of 8% and falling. The other sits at 24%, because almost nothing sells without a sponsored placement. Same ad efficiency on paper. Completely different businesses.
When a "bad" ACoS is a good decision
This is where ACoS does its most expensive lying, because it punishes the exact behaviour that builds accounts.
At launch, a high ACoS is often the correct strategy. You're paying for position, reviews and sales history in a market where nobody knows you exist. We launched a personal care product built from Amazon search demand data, and we kept the opening ad budget deliberately small because its only job was to prove the demand was real before we spent properly. The listing converted at 25% and the first production run sold out. On the dashboard, those early weeks looked like a middling ROAS. In reality they earned the product a bigger budget faster than we expected.
Same story with a consumer brand in a certified category: sustained early investment carried it into its category's top ten inside a month, and much of the growth that followed was organic. An ACoS purist looking at week two would have told us to cut the bids.
A "great" ACoS can be the warning sign
Flip it round. A brand proudly running a 7% ACoS is usually doing it the only way a 7% ACoS can be done: bidding almost entirely on its own brand name and a handful of proven long-tail terms. Safe traffic, cheap conversions, lovely dashboard.
And a business going nowhere. Branded traffic is people who already found you. If none of your spend introduces the brand to strangers, you've capped your growth at the size of your existing audience while competitors buy the category terms you abandoned. Their sales feed their rank. A year later they own the shelf. On Amazon, standing still is a slow way of shrinking, and a beautiful ACoS is often the receipt.
We've covered this trap in more detail in our piece on the PPC advice that's quietly costing you money.
The dial that actually matters is contribution margin
Even TACoS is a means to an end. The number a business lives or dies on is contribution margin: what's left from each sale after product cost, Amazon's fees, fulfilment and advertising. That's the figure that should size your ad budget, because it tells you exactly how much you can afford to pay for a sale and still make money, and how much you can choose to pay for a while when you're deliberately buying growth.
This is how we set budgets for the brands we run. Spend is ring-fenced and tied to what the products genuinely earn per unit, agreed up front, not adjusted by nerves. A launch phase might run margin-neutral on purpose. A mature line might target a TACoS that leaves proper profit. Either way it's a decision, made once, with the real economics on the table.
One caveat, and it matters. No metric survives a broken channel. If unauthorised resellers are undercutting your price and trading the buy box between them, your conversion rates swing, your attribution muddies and every ratio in this article becomes noise. Brands often read that noise as a marketing problem when what's underneath is a control problem, and we've written about where it starts in our piece on why your Amazon price keeps falling.
So, is 22% good? Wrong question. Ask what your TACoS has done over six months and what each sale leaves behind after every fee. If nobody in the business can answer both within a day, that's usually the most profitable audit you'll run this quarter. And if the answers come back uncomfortable, that's a fixable problem.
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