TACoS Explained: Why It Misleads Repeat-Purchase Brands
TACoS is a useful health check, but for repeat-purchase brands it can reward the wrong spend. Here's what to track alongside it.
TACoS is a useful health check, but for brands whose customers reorder, it can reward the wrong spend and punish the right spend.
TACoS has become the metric every Amazon seller and agency quotes. It's a real improvement on judging ads by ACoS alone. But after months of analysing customer data for consumable brands, I've seen TACoS look healthy while a brand was quietly paying to re-buy its own customers, and look worrying while ads were building a valuable customer base.
This article explains what TACoS is, where it misleads repeat-purchase brands, and what to track alongside it.
What TACoS is
TACoS (total advertising cost of sales) is your ad spend as a share of all your sales, not just the sales your ads claim.
TACoS = ad spend ÷ total sales (ad-attributed + organic) × 100
ACoS divides the same ad spend by ad-attributed sales only. So if you spend £1,000 on ads, ads claim £4,000 of sales and your total sales are £10,000, your ACoS is 25% and your TACoS is 10%.
Sellers like TACoS for good reasons:
- It captures the halo. Ads lift organic ranking and sales, and TACoS gives that credit.
- It shows dependence on ads. A falling TACoS with rising sales suggests organic growth is taking over.
- It ties ads to the P&L. It's much easier to compare with your overall margin than ACoS is.
Where TACoS misleads repeat-purchase brands
TACoS treats every sale as equal. For a consumable brand, a sale to a brand-new customer and a sale to someone on their sixth reorder are worth very different things to your ad budget.
1. Branded spend makes it look better than it is
Branded search converts well and is cheap, so it pulls TACoS and ACoS down. But in the AMC data I've analysed, only 41–49% of branded-search purchases came from new-to-brand customers, against 73–83% for category and competitor targeting.
On one product, branded search took half of all ad-attributed purchases. Across several products, 33–55% of ad sales went to people who already bought from the brand. A low TACoS can simply mean you're paying for customers you already had.
2. Loyal customers flatter the denominator
For daily consumables, repeat customers typically generate 65–75% of revenue. Those sales sit in the TACoS denominator, whether or not today's ads had anything to do with them.
So a brand with a strong loyal base can post a low TACoS while its ads acquire almost no one new. The number looks healthy until the loyal base starts to shrink.
3. It ignores the time lag
A new customer's first order is only the start. Customers typically reorder every 1 to 4 months, and a daily-use product can still be earning more than a year later.
TACoS measures spend and sales in the same month. Push hard on acquisition and TACoS rises now, while the payoff arrives over the next 6 to 12 months. Cut acquisition and TACoS falls now, while the damage shows up later.
Worked example: same TACoS, very different health
Here are two made-up supplement brands with identical monthly sales, ad spend and TACoS. Each customer is worth £36 in lifetime profit before ads.
| Brand A | Brand B | |
|---|---|---|
| Total monthly sales | £100,000 | £100,000 |
| Ad spend | £10,000 | £10,000 |
| TACoS | 10% | 10% |
| Share of ad spend on branded search | 60% | 20% |
| New customers from ads | 300 | 700 |
| Cost per new customer | £33.33 | £14.29 |
| LTV : CAC (on lifetime profit) | 1.1× | 2.5× |
On a TACoS dashboard, these brands look the same. In reality, Brand A is barely breaking even on the customers it acquires and relies on a loyal base it isn't replacing. Brand B is building a customer base that will keep paying out for a year or more.
If Brand B then raised spend and its TACoS rose to 13%, a TACoS-only view would call that a problem. A customer-value view would call it the right move.
What to track alongside TACoS
Keep TACoS, but add four numbers that show whether your ads are building the business or just recycling it.
| Metric | How to work it out | What it tells you |
|---|---|---|
| Cost per new customer | Ad spend ÷ new-to-brand customers | What you really pay to grow. It can be 2–3× your cost per order. |
| New-to-brand share by campaign type | New-to-brand purchases ÷ all ad purchases, split by branded, generic, competitor, auto | Which campaigns acquire and which re-buy existing customers |
| Payback month | The month a new customer's cumulative profit covers their acquisition cost | Whether a high ACoS is a problem or an investment |
| Returning buyers as a share of monthly buyers | Repeat buyers ÷ all buyers each month | Whether your loyal base is growing or quietly shrinking |
The first two come from new-to-brand metrics in the ads console, and AMC gives a far more detailed view. Payback needs an estimate of lifetime value, which is exactly what my free LTV calculator gives you.
How to use TACoS properly
- Split it. Report TACoS with and without branded spend. If the non-branded number is much higher, your headline figure is being propped up.
- Watch the trend, not the month. Compare rolling three-month figures so acquisition pushes and their later payoff sit in the same view.
- Set targets by product shape. A daily-use product can afford a higher TACoS than a one-off purchase, because its customers keep paying out.
- Pair every TACoS target with a new-customer target. A falling TACoS alongside falling new customers is a warning, not a win.
- Judge acquisition campaigns on payback. In one account, non-branded campaigns running at a 45–49% ACoS paid back within 8–9 months. A flat TACoS or ACoS target would have cut them.
The bottom line
TACoS tells you how much of your revenue goes on ads. It doesn't tell you whether that spend is winning new customers or re-buying old ones, and for a repeat-purchase brand that's the question that matters.
Start by working out what a customer is worth to you. Try the free Amazon LTV calculator to see your lifetime value, payback month and the ACoS you can really afford.
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