How to Reduce ACoS on Amazon: 6 Tactics That Actually Work

Most ACoS problems aren't bidding problems. That's the first thing worth understanding. When an account comes in with a 60% ACoS, the instinct is to cut bids across the board. Sometimes that's right. But just as often, the real issue is wasted spend on irrelevant keywords, a listing that converts at 4% when it should be converting at 10%, or campaigns structured in a way that makes efficient bidding almost impossible.

Across 2,400+ campaigns managed through Hector AI between January and December 2025, brands that worked through all the structural issues, not just bid levels, reduced ACoS by an average of 34% within 90 days without losing sales volume. Cutting bids alone got them maybe a third of the way there. The rest came from the other five tactics in this guide.

"The brands that struggle most with ACoS are the ones treating it as a single-lever problem. It's not, it's an output of five or six variables all running simultaneously," says Meher Patel, Founder & CEO of Hector AI and Amazon Ads Top 20 Globally Partner. "Fix the right variable and ACoS drops without you touching a single bid."

The 6 tactics at a glance

1. Fix your campaign structure before adjusting any bids

This is the one people skip because it takes longer and feels less satisfying than moving a slider. But if your campaign structure is wrong, you're optimising on top of a broken foundation.

The most common structural problem: auto campaigns and manual campaigns sharing the same budget with no clear separation of purpose. Auto campaigns are for discovery, finding new converting search terms. Manual campaigns are where you concentrate spend on the terms you've already proven work. When they're mixed together, you can't tell which keywords are actually profitable, and you're often bidding against yourself.

The structure that consistently works:

•        Auto campaign: Low bids, $10–20/day budget, review weekly for converting search terms

•        Broad/phrase manual campaign: Medium bids, used to expand reach on proven root keywords

•        Exact match campaign: Highest bids, highest budget, reserved for your best-performing exact match terms

The point of this structure is that your exact match campaign, where your best terms live, should be doing most of your revenue. When that's true, ACoS at the campaign level becomes much easier to manage, because you're controlling spend on a contained set of terms rather than an open-ended auto campaign.

2. Build a proper negative keyword list, not just a few obvious terms

If you've never done a serious negative keyword audit, this is probably where 15–25% of your ad spend is going. Campaigns without a structured negative keyword approach waste an average of 23% of daily budget on irrelevant impressions within the first 30 days of launch; that's not a guess, it's what Hector AI's campaign data shows consistently across new accounts.

The source of truth here is your Search Term Report in Seller Central. Download it, filter for the last 60–90 days, and sort by spend descending. Look for:

•        Search terms with 5+ clicks and zero conversions, add these as exact match negatives

•        Search terms where the ACoS is more than twice your target, add these at phrase or exact match

•        Terms that are completely off-category (someone searching for a different product type entirely)

•        Competitor brand terms if you're not intentionally running conquest campaigns

A few specifics that trip people up: adding negatives at the ad group level vs the campaign level matters. Ad group negatives block a term for that ad group only. Campaign negatives block it across the whole campaign. If a term is completely irrelevant to your product, block it at the campaign level. If it's only irrelevant in a specific ad group's context, use ad group level.

This isn't a one-time exercise. Set a calendar reminder to review the Search Term Report every two weeks. Terms that convert in week one can turn into money-drainers by week eight as your bid environment changes.

3. Set bids using the target ACoS formula, not by feel

Most sellers set bids by feel, adjust them based on whether ACoS went up or down last week, and repeat. The problem is that "last week's ACoS" is a lagging indicator; you're always reacting to something that already happened, and you're baking in a systematic delay that makes it hard to get bids right.

There's a much more direct approach. If you know your target ACoS, your product's conversion rate, and its average order value, you can calculate the exact maximum CPC you should be paying for any keyword:

What this tells you is the maximum you can bid on that keyword and still hit your ACoS target, assuming your conversion rate holds. If you're currently bidding above that number, you're structurally guaranteed to miss your ACoS target regardless of how well the keyword performs.

The practical step: pull your conversion rate from the Campaign Manager for each ad group (it varies significantly by product), calculate the max CPC for each, and compare against what you're actually bidding. Anything above max CPC is a candidate to come down.

Where this gets more nuanced: conversion rates aren't static. A keyword converting at 12% in December might convert at 7% in March. Build a habit of recalculating max CPCs monthly, not just when ACoS spikes.

4. Harvest converting search terms into exact match campaigns

Your auto and broad match campaigns are constantly surfacing search terms, some of which are converting really well. But if those terms stay in auto or broad, you're in a situation where Amazon controls how much you bid on them and when they show. Moving your proven winners into exact match campaigns puts you back in control.

The harvesting process is straightforward:

1.     Pull your Search Term Report filtered for the last 30–60 days

2.     Filter for search terms with conversions and an ACoS below your target

3.     Add these as exact match keywords to a dedicated exact match campaign

4.     Add the same terms as exact match negatives in your auto and broad campaigns (so the same query only competes in your exact match campaign, where you're bidding intentionally)

Why does this reduce ACoS? Two reasons. First, exact match campaigns generally have higher conversion rates than broad or auto, because the query-to-product match is tighter. Second, you can set precise bids for these terms rather than relying on Amazon's automatic bidding, which means you stop overpaying for terms that don't actually need high bids to win.

Campaigns using this keyword harvesting workflow reduced average CPC by 14% while maintaining equivalent conversion rates over 90 days in Hector AI's managed accounts, by concentrating spend on terms with demonstrated purchase intent (Hector AI Internal Data, Q4 2025).

5. Add dayparting rules to stop spending during low-conversion hours

Not all hours convert equally. For most Amazon product categories, evening hours, roughly 7–10 PM local time, and weekends generate higher conversion rates than morning and midday. If you're spending the same amount at 9 AM Tuesday as you are at 8 PM Saturday, you're almost certainly buying a lot of low-quality clicks during those off-peak hours.

Dayparting lets you schedule bid adjustments by hour and day of the week. You're not turning campaigns off; you're reducing bids during times when shoppers are less likely to buy and increasing them when conversion probability is higher.

The setup:

•        Pull your campaign data segmented by hour of day and day of week from the Campaign Manager (Advertising Reports section)

•        Identify hours where your conversion rate consistently drops below half your average

•        Set bid decreases of 25–50% during those windows

•        Set bid increases of 10–20% during your peak conversion windows

Campaigns in Hector AI using dayparting rules generated 22% higher ROAS on weekend traffic compared to equivalent flat-bidding campaigns over the same period (Hector AI Internal Data, Q3 2025). The mechanism isn't magic; you're spending the same total budget, but more of it lands during windows when people are actually ready to buy.

One caveat: dayparting data needs at least 4–6 weeks of history to be reliable. Don't set dayparting rules on a new campaign based on two weeks of data. Wait until the patterns are stable.

6. Improve your listing's conversion rate, the ACoS tactic no one talks about

ACoS is determined by two things: how much you spend, and how much you sell. Every tactic so far has focused on reducing spend. This one increases sales from the same spend, which reduces ACoS without you touching a bid.

The math: a listing converting at 12% generates the same ACoS at a $15 CPC as a listing converting at 8% would at a $10 CPC. If your conversion rate is weak, no amount of bid optimisation will fix your ACoS; you're in a structural hole.

The highest-impact listing improvements for conversion rate:

•        Main image: Click-through rate from search results is the first conversion. If your main image looks generic or small against competitors, your CTR will be low, and you'll pay for every click that does land twice as hard. Test your main image against 2–3 alternatives using Amazon's Manage Your Experiments tool.

•        Title: Frontload your primary keyword and the most relevant product attribute within the first 60 characters. That's what shows in mobile truncation, which is where most Amazon shopping happens.

•        Reviews: Below 15 reviews or below 4 stars, your conversion rate will be well below category average regardless of what you do with bids. If you're in this position, aggressive PPC spend is economically irrational until you fix the reviews problem.

•        Price: Check your price against the buybox competitors every week. A 10% price premium with no obvious quality signal is probably costing you 2–3 percentage points of conversion rate.

•        A+ content / bullet points: Not because Amazon asks for it, but because shoppers who scroll past the fold and read A+ content are genuinely more likely to buy. Thin bullet points that list features without explaining benefits leave real conversion on the table.

The test: if your conversion rate for Sponsored Products is below 8% for a product with 20+ reviews and a competitive price, the listing itself is the primary ACoS problem. Fix the listing before spending more on bids.

Prioritising What Matters When Resources Are Limited

If your ACoS is above 50% and you've never done a structured audit, start with tactics 2 and 1, negative keywords, and campaign structure. These are the most impactful levers and the ones that produce the fastest visible results.

If your ACoS is in the 30–50% range and you have decent campaign structure, add tactic 3 (bid formula) and tactic 4 (keyword harvesting). These are medium-difficulty but compound over time.

If you're trying to get from 25% ACoS to 18% ACoS on an already well-structured account, tactics 5 and 6 are where you go. Dayparting squeezes efficiency at the margin, and listing conversion rate is often the hidden ceiling on how far you can go.

Managing 250+ Campaigns at Scale

At scale, manual reviews of Search Term Reports, bid calculations, and dayparting schedules aren't sustainable. A campaign manager handling 50+ campaigns manually will always have a lag of days or weeks between a keyword starting to overspend and a bid adjustment happening. That lag is where ACoS creep lives.

Automated bid rules handle this continuously, monitoring ACoS at the keyword level and adjusting bids up when you're below target (headroom to grow) and down when you're above target (cost control). Combined with automated negative keyword workflows and dayparting schedules, the manual review cycle shrinks from weekly to exception-based.

Hector AI's rule engine manages this across all campaign types, Sponsored Products, Sponsored Brands, and Sponsored Display, with AMC integration so performance signals from DSP campaigns don't disappear into a separate reporting silo. See how it works: hectorai.live/demo