What you actually pay per click — the second-price auction, demystified.

The single most useful thing to know about Amazon Sponsored Ads is that your bid is not what you pay. Amazon runs a modified second-price auction. You set a maximum you are willing to pay; what you actually pay per winning click is one cent more than the next-highest qualifying bid.

How the auction resolves, click by click

For every shopper query, Amazon assembles the pool of eligible ads, scores each by (bid × predicted click-through rate × predicted conversion rate × historical performance), and ranks them. The top-ranked ad wins the top placement; the runner-up wins the second; and so on. The price each winner pays is calculated to be the minimum bid that would still have won them their slot, given everyone else's scores — typically one cent above the score of the ad directly below them.

Translated: you can bid 1.20 EUR on a keyword and pay 0.74 EUR per click, because the highest other qualifying bid scored equivalent to about 0.73 EUR. The 0.46 EUR gap is auction headroom you never paid for.

Why this changes how you should bid

Because the price is set by the runner-up, bidding aggressively does not necessarily mean paying aggressively. It means winning impressions you would have lost while still paying close to the second-place price. The cost of a higher bid is mostly tail risk on weird auctions where the runner-up happens to be near you, not a uniform premium on every click.

That is why Module 2 episode 24 ends with the headroom rule: the bid should sit above the target CPC. The realised CPC is decided by competitors, not by you; your bid is just the ceiling that decides whether you are eligible to win at all.

What the relevance threshold does

Amazon does not auction every query to the highest bidder. Below a certain relevance score, ads simply do not enter the auction — Amazon will rather show no ad than a bad one. That threshold is why irrelevant keywords with high bids quietly fail to spend. The fix is not raising the bid; it is fixing the relevance (better title, better keyword choice, better page content).

Placement multipliers sit on top of the auction

If your campaign has a top-of-search modifier of +50%, your bid is multiplied by 1.5 specifically for the top-of-search auction. You compete in that slot with the higher effective bid; you still pay one cent above the runner-up. The modifier expands your eligibility to win that placement; it does not floor your CPC.

The practical takeaway

Two things follow. First, look at average CPC vs. bid as a single diagnostic — the wider the gap, the less the bid is the binding constraint. Second, never raise a bid because the CPC came in lower than the bid; that is the auction doing its job, not a signal to spend more.