Amazon PPC Bid Strategies: Fixed vs. Down-Only vs. Up-and-Down

Most guides frame Amazon’s three bid strategies as a lifecycle progression — fixed at launch, loosen to down-only as the product matures, open up to up-and-down once you’re established. In practice, that’s not how this actually plays out.

Short answer: down-only bidding wins on roughly 95% of campaigns, because it captures cheaper clicks for free whenever they’re available. Fixed and up-and-down are narrow tools for specific situations — a known cost-per-click target, or a brand-new keyword with genuinely no data — not everyday defaults, and the choice between them comes down to what you know about that keyword, not how mature the product is.

Fixed Bids: When to Use It

Fixed is one of the least-used strategies, and for good reason — it boxes you into a specific bid, which in most situations isn’t what you actually want.

The real use case: you have a very specific target in mind. You know exactly what max cost-per-click you need to hit a target ACOS you’re happy with. Fixed bidding effectively guarantees that target, as long as you convert at the rate you have data on (or genuinely believe you’ll achieve). It’s a precision tool for a known, specific CPC target — not a general-purpose default.

Down-Only Bids: When to Use It

This is by far the most used strategy — it runs on roughly 95% of campaigns. The mechanism is simple: you set your bid as a ceiling, and Amazon can lower it opportunistically whenever a cheaper click is available on that keyword — whether because your bid is simply higher than what other sellers are bidding, or because of time-of-day effects, like the middle of the night when competitors are out of budget or not advertising. If you’re converting at the same rate on those cheaper clicks, there’s no reason to pass on them. It just lowers your ACOS for free.

This is especially valuable on lower-volume keywords that don’t have a suggested bid — with no real market signal to base a number on, you can set something like £1.50 as a safe ceiling, fully expecting it’s above the true market rate. Down-only bidding will often actually win clicks around £0.60 instead. Fixed bidding would have locked you into paying the full £1.50 for no reason.

Up-and-Down Bids: When to Use It

Up-and-down lets Amazon increase your bid by up to 100% — the only one of the three strategies that lets Amazon bid above your set amount, when it predicts a higher chance of conversion.

The primary use case is the mirror image of the down-only scenario above: brand-new product launches, on keywords with genuinely no data yet. Instead of a bid that’s too high, this solves for a bid guess that turns out to be too low relative to what other advertisers are actually paying. With fixed or down-only bidding stuck at, say, a £1.50 ceiling and getting no impressions, the only fix is manually raising the bid and re-checking every few days — slow. Up-and-down lets Amazon bid up to £2–3 on that same £1–1.50 base automatically, which gets you usable data much faster during launch, when speed of learning matters more than cost efficiency.

The real cost: giving Amazon room to bid more on your behalf means Amazon will use that room whenever it can. This needs active monitoring — it isn’t something to set and leave.

Common Mistakes

The biggest mistake, by a wide margin: leaving up-and-down bidding running unmonitored for too long. This shows up constantly on account takeovers — check a campaign in week one and it looks fine, reasonable CPCs. Come back a week later and ACOS has climbed 50-60%, purely because cost-per-click crept upward while nobody was watching. Amazon used exactly the headroom it was given.

If you’re not deep into optimizing every campaign yourself, the safer default is down-only. It’s lower-maintenance, and it will generally save you money over time through cheaper clicks and a better baseline ACOS. Up-and-down should be a deliberate, actively-monitored choice for a specific situation (usually launch data collection) — not something left running by default.

FAQ

Which bid strategy should I default to if I’m not sure? Down-only. It’s lower-maintenance, generally produces a better ACOS through cheaper clicks, and doesn’t need the active monitoring the other two require.

Is up-and-down bidding safe to leave running long-term? Not really — it needs active, regular monitoring. Left unchecked, cost-per-click tends to creep upward as Amazon uses the bidding headroom it’s been given, and by the time you notice, ACOS can already be 50-60% higher than when you last checked.

Does my bid strategy need to change as my product moves through its lifecycle? Not strictly by lifecycle stage — it’s really about whether you have reliable data on a given keyword. New or low-volume keywords with no suggested bid are where down-only and up-and-down do their most useful work, rescuing an overpriced or underpriced guess. Once a keyword has real conversion history, the choice comes down to your specific goal for it, not how old the product is.

When does fixed bidding actually make sense? When you have a specific target ACOS and a known (or confidently estimated) conversion rate — fixed bidding locks in the exact CPC needed to hit that number, at the cost of missing any cheaper-click opportunities down-only would have captured.

How do I know if up-and-down bidding is quietly costing me money? Check cost-per-click and ACOS trend weekly, not just at setup. The risk isn’t a one-time bad bid — it’s gradual creep that’s easy to miss until it’s already a 50%+ jump.