Amazon PPC Bid Strategy: Dynamic Bids Down-Only vs Up-and-Down vs Fixed, Explained

By Abdul Saboor, Founder of QREZYN ·

If you've ever opened a new Sponsored Products campaign and stared at the three options under "bidding strategy," you already know the confusion: Dynamic bids – down only, Dynamic bids – up and down, or Fixed bids. Picking the right Amazon PPC bid strategy for dynamic bids isn't a one-time setting you choose and forget — it directly changes how aggressively Amazon can raise or lower what you actually pay at the moment of auction, which means it directly changes your ACoS.

Here's the short answer: use Dynamic bids – down only when you want control and predictability (most campaigns, especially new or unproven ones). Use Dynamic bids – up and down only on campaigns with strong, proven conversion data where you want Amazon to chase high-intent impressions. Avoid Fixed bids almost entirely — it sounds safe, but it just means Amazon won't lower your bid in low-converting placements, which quietly wastes spend. The rest of this post breaks down exactly why, plus how placement modifiers stack on top of whichever strategy you choose.

What dynamic bids actually do at auction time

Your bid is not what you pay — it's the ceiling Amazon is allowed to work with. The "bidding strategy" setting tells Amazon how much it's allowed to move that ceiling up or down in real time, based on how likely a given impression is to convert.

  • Dynamic bids – down only: Amazon can lower your bid by up to 100% when it predicts a click is unlikely to convert, but it will never raise it above what you set. This is the default for a reason — it's the only strategy that can't accidentally cost you more than your stated bid.
  • Dynamic bids – up and down: Amazon can lower your bid the same way, but it can also raise it by up to 100% (up to 50% for Product Display placements) when the algorithm predicts a high-converting opportunity — most commonly top-of-search real estate. This is where "down only" vs "up and down" decisions matter most, because that upward flex can double your actual cost-per-click on a single impression.
  • Fixed bids: Amazon doesn't adjust anything. You pay close to your exact bid regardless of how likely the click is to convert. It feels predictable, but it means you lose the one thing dynamic bidding is good at — automatically paying less for junk impressions.

Down-only vs up-and-down vs fixed: when to use each

Match the strategy to the maturity and purpose of the campaign, not to a blanket rule across your whole account.

  • Use Down Only for: brand-new campaigns, new product launches, broad/discovery campaigns, and anything where you don't yet have conversion data to trust. It lets the algorithm trim waste without any risk of overpaying.
  • Use Up and Down for: exact-match campaigns on proven converting keywords, retargeting-style ASIN campaigns, or defense campaigns on your own branded terms where you already know the keyword converts and winning the top slot is worth paying extra for. Only flip this on once you have at least 2-4 weeks of stable conversion data on that specific campaign.
  • Avoid Fixed Bids for: almost everything. The only real use case is extremely tight manual bid testing where you want zero algorithmic interference — rare, and usually not worth the tradeoff for most sellers managing ad spend without a dedicated analyst watching daily.

Placement modifiers: the setting most sellers ignore

Placement modifiers sit on top of your bidding strategy and are, frankly, where most sellers leave money on the table. Under each campaign's bidding section, Amazon lets you add a percentage increase for two placement types: Top of Search (first page) and Product Pages/Rest of Search.

Here's the mechanic that trips people up: placement modifiers are applied in addition to whatever your dynamic bid strategy already did. If you're running Up and Down bidding with a 50% Top of Search modifier, Amazon can theoretically raise your effective bid well beyond your base bid in a single auction. That's not a bug — it's by design for sellers chasing visibility — but it means you should never set aggressive Top of Search modifiers and Up and Down bidding at the same time without watching ACoS closely for the first week.

A more disciplined approach: start with a 0% placement modifier on new campaigns and let the bidding strategy alone do the work for the first week or two. Once you can see in the Placement report which placement actually converts for that specific campaign (Top of Search almost always converts higher for branded/high-intent terms; Rest of Search and Product Pages often convert better for discovery or complementary-product targeting), add modifiers surgically to the placement that's already proving itself — not as a blanket "just in case" setting.

A simple framework to stop guessing

  • Weeks 1-2 of a new campaign: Dynamic bids – down only, 0% placement modifiers. Let data accumulate.
  • Weeks 3-4: Review the Placement report and Search Term report. Identify which placement and which keywords are converting below your target ACoS.
  • Week 5+: Add Top of Search modifiers only to campaigns/keywords with proven conversion rate. Consider switching those specific campaigns (not the whole account) to Dynamic bids – up and down.
  • Ongoing: Revisit every 30 days. Seasonality, competitor bidding, and your own listing conversion rate all shift what the "right" strategy is — a setting that was correct in Q2 can be bleeding money by Q4.

The part that's easy to miss: this isn't a "set it once" decision across your whole catalog. A campaign on a hero SKU with a 20% conversion rate should probably be handled completely differently than a campaign on a slow-moving accessory — yet most sellers apply the same bidding strategy account-wide simply because it's faster.

When it makes sense to get expert help

If you're managing more than a handful of campaigns, the math gets complicated fast — multiply three bidding strategies by two placement modifiers by dozens of keywords and ASIN targets, and "optimizing bids" becomes a weekly spreadsheet job most business owners don't have time for. That's usually the point where ad spend creeps up faster than sales, and nobody notices until the monthly statement.

QREZYN manages Amazon PPC accounts daily — adjusting bidding strategy campaign-by-campaign, tuning placement modifiers against real conversion data, and reallocating spend toward what's actually profitable instead of just what's running. If you want a clear picture of where your current bid strategy is helping or hurting you, grab a free Amazon audit from QREZYN — we'll show you exactly where your ad spend is working and where it's quietly leaking before you commit to another month of guessing.