Amazon ACOS: Understanding and Optimising Profitability

ACOS is the most watched and most misused metric in Amazon Ads. Many sellers set a 20% target because they read it somewhere, cut every campaign above it, and watch total revenue fall the following month. The problem is not ACOS itself, it is reading it alone, without a margin benchmark and without TACOS beside it. This article explains how to calculate both indicators, what level to aim for depending on your situation, and what decisions to actually take in your campaigns.

What ACOS measures exactly

ACOS stands for Advertising Cost of Sale. The calculation is simple:

ACOS = ad spend / revenue generated by advertising x 100

Example: you spend 500 euros on Amazon Ads and those clicks generate 2,500 euros of attributed sales. Your ACOS is 20%.

The trap is in the denominator. ACOS only counts sales attributed to advertising, within a 7 day attribution window for Sponsored Products. It completely ignores organic sales, the ones that arrive because your listing ranks well, often thanks to the sales history advertising itself created.

In other words, ACOS measures the efficiency of a channel, not the health of an account.

The only benchmark that counts: break-even ACOS

Before targeting a number, calculate your advertising break-even. Break-even ACOS equals your gross margin expressed as a percentage of the selling price excluding VAT, before advertising.

Take the same product sold at 29.90 euros including VAT in Belgium:

Gross margin: 9.90 / 24.71 = 40%. Your break-even ACOS is therefore 40%. Below it, every advertised sale earns money. Above it, it costs money.

From that threshold, set a target ACOS based on your objective:

• Launching a reference: 60 to 100%, for four to six weeks. You are buying sales history and reviews, not margin.
• Profitable growth: 25 to 35% in our example, roughly 70 to 85% of break-even ACOS.
• Profit maximisation: 15 to 20%, with volume mechanically falling.
• Defending a position: close to break-even, on brand queries and listings a competitor is attacking.

These thresholds depend directly on your cost structure. A product at 65% gross margin and one at 30% cannot be steered to the same target, as the fee breakdown in our guide to selling on Amazon in Belgium shows.

TACOS, the indicator that reveals the real trend

TACOS stands for Total Advertising Cost of Sale:

TACOS = ad spend / total revenue x 100

This time the denominator includes all sales, advertised and organic. Read month after month, it tells a story ACOS cannot tell.

ACOS is stable and unimpressive. TACOS, on the other hand, drops from 25 to 15%: advertising is pushing organic ranking, which takes over. That is exactly the behaviour you want in a successful launch.

The reverse scenario is a warning sign: rising TACOS while ACOS stays stable means your organic sales are eroding and advertising is compensating for lost position. The cause is often a past stockout, a drop in customer rating, or a competitor taking the Buy Box.

Remember the reading rule: ACOS steers campaigns, TACOS steers the brand.

Five optimisation levers that actually work

1. Isolate brand queries

Your own brand queries convert extremely well and show a very low ACOS, often under 10%. Mixed into generic campaigns, they artificially lower the average ACOS and hide loss-making campaigns. Always separate them into a dedicated campaign, and analyse the rest without them.

2. Work the search term report

The search term report is the most profitable decision source in the account. Every week, filter on 30 days:

• terms with more than 15 clicks and zero orders: move them to negative keywords;
• terms converting under your target ACOS: promote them to an exact campaign with a dedicated bid;
• relevant but expensive terms: cut the bid by 15 to 20% rather than pausing.

3. Do not cut too fast

A keyword with only 8 clicks tells you nothing statistically reliable. A reasonable decision threshold is around 10 times the inverse of your conversion rate. At a 10% rate, wait for roughly 100 clicks before deciding.

4. Fix the listing before the bid

An ACOS that is too high rarely comes from the campaign. Break it down: a weak click-through rate signals a main image or price problem, a weak conversion rate a listing, review or availability problem. Lowering bids on a listing that converts badly only reduces volume without fixing the cause. Our Amazon SEO page details that listing work.

5. Steer by product group, not globally

A global ACOS of 28% can easily hide one product at 12% and another at 55%. Segment by reference or product family, with a target ACOS specific to each, derived from its margin. That is the basis of a healthy campaign structure, detailed on our Amazon Ads page.

FAQ

What is a good ACOS on Amazon? There is no universal good ACOS. The only valid benchmark is your break-even ACOS, that is your gross margin as a percentage. If your gross margin is 35%, a 30% ACOS is still profitable and a 40% ACOS loses you money.

What is the difference between ACOS and TACOS? ACOS compares ad spend to sales generated by advertising only. TACOS compares it to total revenue, advertised and organic combined. TACOS measures your brand's real dependence on advertising.

Is a high ACOS always bad? No. On a launch, an ACOS of 60 to 100% for four to six weeks is an investment in acquiring position, provided TACOS falls afterwards.

How often should campaigns be optimised? Weekly steering on 14 to 30 days of data is enough in most cases. Adjusting bids every day amounts to reacting to statistical noise.

Conclusion: three numbers to know by heart

Before opening your next Amazon Ads session, have these three numbers in mind: your gross margin as a percentage, and therefore your break-even ACOS; your target ACOS for this quarter's objective; and your TACOS over the last three months. With those three benchmarks, most bidding decisions become obvious.

If you want to know where your advertising budget actually goes, we offer a free Amazon Ads account audit: campaign structure analysis, break-even ACOS calculation per reference and identification of unprofitable spend. Contact Let It Grow to receive your audit.