What Is a Good ACoS for Amazon FBA? Find Your Break-Even Number

Ask this in any seller group and somebody will say 25%. Somebody else will say under 20%. Both answers are useless, and not because the people giving them are wrong — because the question is missing its second half.

ACoS on its own means nothing. ACoS relative to your margin means everything. A 30% ACoS is comfortably profitable on one product in your catalogue and quietly losing money on the one next to it.

Here is the number that actually answers the question, and how to calculate it per SKU.

Break-even ACoS is just your margin

Break-even ACoS = net profit margin before advertising

That is the whole formula. If a product clears 41.4% of its sale price after referral fee, fulfilment fee, storage, cost of goods and inbound shipping, then at a 41.4% ACoS every dollar of profit the ad generates is spent on the ad that generated it.

Check it on the bamboo cutting board used across this cluster:

At a 41.4% ACoS you spend $10.34 in ads to make $10.34 in profit on a $24.99 sale. Above it you are paying for the privilege. Below it you are making money.

(All fee figures here are assumptions chosen to be plausible, not quoted rates. Use your own.)

Which is why “a good ACoS” is different for every SKU

Run the calculation across a catalogue and the point makes itself:

Same account, same advertising team, same 30% ACoS — profitable on two products and destructive on two others. Any target ACoS applied across a whole account is guaranteed to be too loose for the thin products and too tight for the fat ones.

Put a break-even ACoS column next to your actual ACoS column, colour the gap, and you have replaced an opinion with a per-SKU decision rule.

What the gap is worth in dollars

Percentages are hard to feel. Convert them.

The cutting board’s month: $410 of ad spend produced $2,399.04 of ad-attributed sales. That is a 17.1% ACoS against a 41.4% break-even.

That campaign has $583 of headroom. Which means the correct move is almost certainly not to cut the ACoS — it is to spend more, because there is room to buy additional sales all the way up to a 41.4% ACoS before the last dollar stops paying for itself.

This is the trap in treating a low ACoS as the goal. A 12% ACoS on $800 of ad sales is a worse outcome than a 30% ACoS on $6,000 of ad sales, and the seller optimising for the first number will be delighted while making less money.

TACoS, and the problem ACoS cannot see

ACoS only looks at ad-attributed sales, which means it is blind to the health of the listing underneath.

TACoS fixes that:

TACoS = ad spend ÷ total sales (ads + organic)

For the cutting board: $410 ÷ $7,996.80 = 5.1%.

Now watch what a deteriorating listing looks like when you track both:

ACoS improved every month. By the ACoS-only view this is a campaign getting better and better, and the person running it should be congratulated.

TACoS says the opposite. Ad spend has almost doubled, total sales have moved 27%, and the share of revenue arriving organically has collapsed from 58% to 32%. The ads are not growing the business any more — they are replacing sales the listing used to win for free. Something happened around month 2: a competitor, a review problem, a rank slide.

Track both, every month. ACoS grades the campaign. TACoS grades the product.

When running above break-even is the right call

There is one clear case: launch. A new listing has no rank, no reviews and no sales velocity, and paid traffic is how you buy the first two. Running at a 60% ACoS against a 41.4% break-even is a deliberate investment, not a mistake.

The discipline is to size it in dollars with a stopping rule, because “we’ll fix the ACoS once it ranks” is how a campaign ends up unprofitable for seven months.

The excess above break-even is 60% − 41.4% = 18.6% of ad sales. So:

• A $1,500 launch budget funds $1,500 ÷ 0.186 = $8,065 of ad-driven sales at that ACoS
• At $24.99 a unit, that is roughly 323 units
• When the $1,500 is spent, the launch phase is over and the target reverts to break-even

Write those three numbers down before you start the campaign. A launch budget you can monitor is a completely different thing from a tolerance you keep extending.

Four columns on your PPC tab

That is all this needs:

Sort by headroom. Negative rows are losing money right now and need a bid cut or a pause. Large positive rows are underspending and can take more budget. That sort is the weekly PPC review, and it takes about five minutes.

Pull the break-even ACoS straight from the product row rather than typing it, so a price change or a fee increase updates every ad target automatically — otherwise you will be measuring this quarter’s campaigns against last year’s margins.

For where that margin figure comes from, see how much Amazon FBA costs per unit and how to calculate your break-even price. For the full monthly picture including returns and the plan fee, see the Amazon FBA profit calculator spreadsheet guide.