Amazon Ads Dynamic Bidding: Fixed, Down Only, and Up and Down

Amazon Ads bidding options determine whether a bid stays fixed or changes in response to the platform’s estimate of a conversion opportunity. Fixed bids hold the advertiser’s entered bid; dynamic down-only can reduce it; dynamic up-and-down can raise or lower it. None guarantees a particular ACoS or sales result.

Fixed bids keep the entered bid stable

With fixed bidding, the platform uses the entered bid without dynamically adjusting it based on its conversion estimate. This can make a controlled bid test easier to interpret, though actual cost and delivery still depend on auctions, competition, and other campaign settings.

A fixed bid is not necessarily the most stable business outcome. If traffic mix changes, the same bid can produce different costs and conversions.

• Use when you need a consistent bid input for comparison.
• Monitor spend and conversion quality as auction conditions change.
• Keep placement adjustments in view when evaluating effective bids.

Dynamic options change bids by opportunity

Down-only strategies can reduce a bid when the system estimates a lower likelihood of conversion. Up-and-down strategies can raise or reduce a bid based on estimated likelihood. Exact rules and limits depend on the campaign and the platform’s current settings.

The strategy needs reliable sales signals to optimize effectively. If conversion tracking, listing eligibility, or attributed sales are incomplete, bid changes may respond to an imperfect picture.

• Choose a strategy that matches the campaign’s goal and data maturity.
• Check the actual setting at the campaign level.
• Allow enough time for conversions to be reported before judging results.

Test the strategy with guardrails

Compare strategies on similar products, targets, and time periods. Track spend, attributed sales, contribution margin, and stock. Avoid changing bids, placement modifiers, and targeting at the same time if the goal is to understand which control changed the result.

Treat bid strategy as an input, not a substitute for campaign design. Keep budgets and acceptable economics explicit, then review whether the resulting traffic is useful.

A bid strategy should be evaluated against the same target set and budget conditions. If you change the strategy and simultaneously add new targets or increase budget, a result change cannot be attributed to bidding alone. Use an observation period that covers normal variation in demand and allow the reporting window to mature.