Should you spend more or less on every Amazon product you sell?

Most Amazon sellers run ads to a cost target. ACOS, ROAS, a blended MER. That number hides the thing that matters. In ROAS, a dollar that wins a brand-new customer looks the same as a dollar that rings up a sale you would have made anyway. They are not worth the same amount.

Every ad dollar answers two questions. Most reports show only the first. Put both together and the right move often flips. The keyword your ROAS dashboard loves can be the one quietly wasting money.

Two questions every ad dollar has to answer

Question 1, the customer: is this customer worth acquiring? Measured by the spend curve: lifetime profit divided by acquisition cost (LTP:CAC), using real realized profit, plus how quickly returns diminish as you spend more.

Question 2, the keyword: is this keyword acquiring anyone? Measured by the new-to-brand rate: the share of ad-driven orders that came from someone who had never bought the brand before. Above 50 percent means new customers. Below 50 percent means returning ones.

Neither number is enough on its own. A high-value customer bought through a returning-customer keyword was not really acquired. A cheap new customer on a product no one reorders adds little. Read the two together and the next dollar knows where to go.

The playbook, in six steps

Run it on every product, not just the top sellers. Start at the top for quick wins. Then keep going. The long tail is where wasted spend usually hides.

1. Rank every product, top first. Start where the acquisition volume is, then keep going. No product should escape the two questions.
2. Read each product’s spend curve. LTP:CAC, the acquisition cost, and how fast the next dollar loses efficiency (with a confidence score, so you know when to trust the curve).
3. Sort into spend-more and spend-less. Scale, grow, hold, or reduce, based on LTP:CAC, using the diminishing-returns curve only where it is statistically reliable.
4. Pull the keywords behind those products. Top search terms per product, branded versus non-branded, ranked by purchase share, with a funnel read that flags listing problems masquerading as spend problems.
5. Score each keyword’s new-to-brand rate. Keyword by keyword: is this term bringing in new customers, or re-selling to existing ones?
6. Measure the split, then set each keyword’s ACOS ceiling. For each product, work out what share of its ad spend goes to acquiring keywords versus returning ones. Then set a spend limit per keyword. A keyword that acquires new customers earns a higher limit, because the customer pays back over a year.
7. Cross the two and reallocate. Spend more on high-NTB keywords for valuable customers. Spend less on low-NTB returning keywords. For a valuable product stuck on those keywords, open new acquisition routes rather than bidding up the same terms.

Steps 1 to 3: the spend curve

This account sells health supplements on Amazon. The table shows the top products, but the read runs on every SKU. The bands are simple: Scale at 4x or more, Grow from 2.5x to 4x, Hold from 1.5x to 2.5x, Reduce below 1.5x. The last column shows whether the response curve was reliable enough to trust.

Two facts drive the rest. The flagship brings in most of the new customers, so it sets the budget. And nothing clears the 4x Scale line. This is a solid, competitive catalog. The gains come from moving money around, not from one breakout product.

Step 4: the keywords

Next come the search terms behind each product, ranked by purchase share. Purchase share is your slice of every purchase on a keyword across the whole market, not just the sales from your ads. Branded terms in this account convert at 60 to 98 percent share but drive only about 10 percent of purchases. The other 90 percent happen on generic category terms. That is where the market is.

Purchase share does a second job, and this is the part most sellers skip. Hold 10 percent of a keyword and 90 percent of its buyers are still open. Hold 1 percent and 99 percent are. That gap is your room to grow. It also predicts new-to-brand before Amazon Marketing Cloud is even open. A keyword you barely hold is full of shoppers who do not know the brand, so ads there tend to bring new customers. A keyword you already own is mostly your own buyers, so ads there mostly reach returning customers. Low share points to acquisition. High share points to returning ones. The new-to-brand pull confirms it.

The funnel shape is the last check. When a product’s share rises from impressions to clicks to cart to purchase, it wins once shoppers see it. The only limit is how often it shows, and spend fixes that. The flagship is the clear case: about 5 percent impression share, but 19 to 31 percent purchase share on generic terms. When share falls through the funnel, the page is the problem, not the bid. The weakest SKU drops from cart to purchase, so its page comes before any budget.

Step 5: new-to-brand, keyword by keyword

Now the second axis, pulled from Amazon Marketing Cloud at the keyword level. It separates a term that merely ran ads from a term that actually brought in new customers.

The flagship earns its acquisition budget. Its generic terms run 60 to 91 percent new-to-brand, and it even wins new customers on a competitor’s brand name. Put its extra spend on those generic terms, not on the branded ones it already owns.

Step 6: where your dollars actually go, and the ACOS ceiling

Two numbers turn the read into a spend decision.

First, the split. Add up each product’s ad spend. Split it in two: spend on acquiring keywords (new-to-brand over 50 percent) and spend on returning keywords (under 50 percent). One number per product, and most sellers never look at it.

The flagship is already right. 93 percent of its spend acquires. Leave it. The smaller products run the other way. On three of them, 60 to 70 percent of the spend goes to returning buyers the brand would have kept anyway. That is the leak, and ROAS kept it hidden because every product looked fine.

Second, the ceiling. ACOS is ad spend divided by ad sales on a keyword. Contribution margin here is about 58 percent. At 58 percent ACOS, ads eat all the first-order profit. Most sellers stop at that line.

A new customer is worth more than one order. Here, a new flagship customer returns about 1.26 times the first order in profit over a year. So a keyword that brings new customers can cost more than the first order and still pay off. The ceiling climbs with the new-to-brand rate:

Look at the bottom two rows. When 80 percent of buyers are new, 112 percent ACOS still turns a profit. The ad costs more than the first order returns, on purpose, because most of those buyers come back. ROAS would cut that keyword. The rule runs both ways: on a returning keyword the ceiling drops to the margin, so cap those at 58 percent. The formula: ceiling = margin + new-to-brand rate × (lifetime multiple − margin).

This is how you add spend without guessing. Compare each keyword’s ACOS to its ceiling. Below the ceiling, add budget. Above it, even the generous version, pull back. On a product that already acquires well, that comparison is the whole job.

Step 7: cross the two axes

Place each product on the grid of customer value against keyword new-to-brand. The plan falls out.

One more check before spending. A separate ExpandFi measure of acquisition efficiency, built from different data, splits these products the same way: the flagship acquiring, the weak and crowded ones reaching returning customers. Two methods with no shared inputs land in the same place. That is enough to act on.

What to do

• Leave the flagship’s split alone. 93 percent acquiring is already right. Tune it by the ceiling: move budget off the few head terms running above their limit, onto the high-new-to-brand terms sitting below it.
• Cut the returning-customer spend on the smaller products. That is where most of the waste sits. Where a product is worth keeping, find higher-new-to-brand terms to acquire on instead of dropping it.
• Fix the weakest product’s page before adding spend. Its funnel leaks at the cart. Ads cannot fix a page.
• Treat branded search as defense, not growth. It converts well, but it is a small slice and mostly reaches buyers who already know the brand.

Run it yourself: the prompt

Here is the whole workflow as a single prompt you can run on your own catalog. It assumes access to a spend-curve report, Brand Analytics search-term data, and Amazon Marketing Cloud (the new-to-brand source).

# Run this across my ENTIRE catalog for [MARKETPLACE], top products first

1. Pull ALL my products from a spend-curve / CAC report, ranked by
   acquisition volume. Start with the top for the fastest wins, then work
   down through every product. For each, get LTP:CAC, effective CAC, the
   spend-response factor, and the model's confidence (r-squared).

2. Classify each product: SCALE (LTP:CAC 4x+), GROW (2.5-4x),
   HOLD (1.5-2.5x), REDUCE (under 1.5x). Only trust the response factor
   where the model is reliable (r-squared >= 0.35); otherwise decide on
   the LTP:CAC ratio alone.

3. For each product (start with SCALE and GROW, then the rest), pull my
   search keywords from Brand Analytics / Search Query Performance. Split
   branded vs non-branded, rank by purchase share, and flag any product
   whose funnel LEAKS (share falls from click to cart to purchase) as a
   listing fix, not a spend play.

4. Pull keyword-level new-to-brand (NTB) rates from Amazon Marketing
   Cloud. Segment: HIGH-NTB (over 50%, acquiring new customers) vs
   LOW-NTB (under 50%, returning customers).

5. Cross the two axes:
   - Spend MORE on high-NTB keywords for products with strong LTP:CAC.
   - Spend LESS on low-NTB keywords (unless it is deliberate brand defense).
   - For a valuable product whose keywords are ALL low-NTB, find NEW
     higher-NTB acquisition routes instead of bidding up the returning terms.

6. Before executing: verify any CAC that does not reconcile with spend
   and volume, confirm more than two weeks of inventory on scale
   candidates, and re-pull NTB on a window ending about 14 days ago.

Figures come from one real Amazon account, shown as ratios and percentages, as a worked example rather than a benchmark. New-to-brand is a Sponsored Products measure from Amazon Marketing Cloud, on a roughly two-week lag. The clean room reports spend low, so the spend split and the ceilings hold, since they do not depend on it, while exact ACOS stays directional. This is a planning method, not a guarantee. Seasonality, competitors, and launches are not modeled. Read your own numbers.