Base Bid
The base bid is the unmodified bid value an advertiser submits at the keyword, product-target or ad-group level — before placement modifiers, dynamic-bid shading and relevance adjustments are applied. It is the single number every other bidding mechanic multiplies against.
The base bid is the raw, unmodified bid value an advertiser submits at the keyword, product-target or ad-group level — before any placement modifier, dynamic-bid shading, or relevance adjustment. It is the number you literally type into Sponsored Products; everything else is a multiplier on top.
Treating the base bid as the bid is the most common bidding mistake on Amazon. The base bid is a starting input; the effective bid that enters the ad auction is almost always different.
Base bid vs effective bid
Effective Bid = Base Bid
× (1 + Placement Modifier)
× Dynamic-Bid Shading (0.5× – 2.0×)
A €0.80 base bid with a +50% top-of-search modifier and Up & Down dynamic bidding can enter the auction anywhere from €0.40 (down-shaded, off ToS) to €2.40 (up-shaded, on ToS). The base bid is the centre of a range, not a price.
Where base bid is set
Three places, in priority order:
- Per-target base bid (keyword or product target) — overrides everything below.
- Ad-group default base bid — applies to targets without an override.
- No bid set — the campaign cannot enter auctions (this happens on new targets if the operator forgets to set one).
The recommended pattern: set the ad-group default to the cluster's centre of gravity, override individual targets only when CVR diverges materially (>30% from cluster average).
Calculating a defensible base bid
The default math, working backwards from desired ACOS:
Max Bid = ASP × CVR × Target ACOS
= €25 × 8% × 30%
= €0.60
This is the break-even base bid at target ACOS, assuming current CVR holds. It is the ceiling for the base bid on that target. Most operators set base bids 60–85% of this break-even ceiling to leave room for dynamic shading upward.
For a new target without CVR history, the defensible starting base bid is:
- Category CVR benchmark × ASP × Target ACOS × 0.7 (discount for unknown relevance)
Base bid by match type and target type
Same root keyword, different match types should rarely share a base bid:
| Target | Typical base bid (relative) | Why |
|---|---|---|
| Branded exact | 1.0× (baseline) | Highest CVR; safest bid |
| Generic exact | 0.7–0.9× | Lower CVR than branded |
| Generic phrase | 0.5–0.7× | Wider match → lower CVR |
| Generic broad | 0.3–0.5× | Widest match → most variable CVR |
| Competitor PAT | 0.6–0.8× | Lower CVR than branded, higher than category PAT |
| Category PAT | 0.4–0.6× | Broadest, lowest predicted CVR |
These are starting points. Real bids drift to the CVR data within 30–60 clicks of evidence.
How base bid interacts with the auction
The base bid signals the advertiser's max willingness to pay before shading. The auction:
- Applies placement modifier → max effective bid at that placement.
- Applies dynamic shading → final effective bid.
- Ranks against competing effective bids.
- Awards slots; charges second-price.
A higher base bid does not always win at more cost — second-price means you pay just enough to beat the next-highest effective bid. Under-bidding the base, however, loses auctions silently without saving CPC on the auctions you would still have won.
Common mistakes
- Treating base bid as the price paid. It's the max input to a shaded second-price auction.
- Setting the same base bid across match types. Broad and exact need different base bids for the same root keyword.
- Forgetting to override ad-group default on outlier targets. A 14% CVR keyword in a cluster averaging 6% should be bid up explicitly.
- Cutting base bid when CPC rises. Often the wrong response — investigate auction pressure, modifier, dynamic-shading first.