ACoS, Advertising Cost of Sale, is the number every Amazon seller watches most closely. It is the percentage of ad-attributed revenue that went to ad spend. A 30 percent ACoS means you spent $30 in ads for every $100 in sales those ads drove.
High ACoS is not always a problem. A new product launch may justify 60 percent ACoS to build sales velocity and organic rank. But for most established products, a persistently high ACoS means your campaigns are leaking money somewhere. Here is how to find it and fix it.
What "high" actually means
ACoS targets depend on your margins. A product with 60 percent gross margin can tolerate much higher ACoS than a product at 20 percent. Before optimizing anything, calculate your break-even ACoS: if your gross margin is 40 percent, your break-even ACoS is 40 percent. Anything above that means advertising is costing you money on a per-sale basis.
Target ACoS is typically set 10-15 points below break-even, leaving room for returns, fees, and margin protection. If your target is 25 percent and your actual ACoS is 45 percent, you have a 20-point gap to close.
The five most common causes of high ACoS
1. Broad match keywords attracting irrelevant traffic
Auto campaigns and broad match keywords generate impressions and clicks from searches that have nothing to do with your product. These clicks cost money and rarely convert, which pushes ACoS up directly.
The fix: pull your search term report weekly and add irrelevant terms as negative keywords. This is not a one-time task. New irrelevant terms appear constantly, especially after Amazon changes its matching algorithms.
2. Campaigns running during low-conversion hours
Most Amazon categories see dramatically different conversion rates by time of day. Late-night and early-morning hours often generate clicks, people browse, but conversions happen during shopping hours when buyers are ready to purchase.
If your campaigns run flat across all 24 hours, you are collecting low-intent clicks overnight and paying the same CPC for them as you pay for high-intent afternoon clicks. Dayparting solves this by concentrating your budget on hours with demonstrated conversion rates. The cost of running campaigns overnight is often larger than sellers realize until they actually measure it.
3. Budget exhausting before peak hours
A campaign that runs out of budget at 11am has zero opportunity to capture afternoon and evening conversions. The ACoS on that campaign will look artificially high because it spent all its budget during low-conversion morning hours and then went dark.
Budget rules that pace spend across the day prevent this. If your campaigns regularly exhaust budget before 3pm, your ACoS problem may be a budget timing problem, not a bid or keyword problem.
4. Bids set too high for placement performance
Top-of-search placements are expensive. They also do not always convert better than product page placements. Many sellers set aggressive bids to win top-of-search positions and find their ACoS is worse than when they ranked lower at lower CPCs.
Audit your placement performance in the campaign manager. If product page placements are generating lower ACoS than top-of-search at a fraction of the cost, your bid modifiers should reflect that.
5. Campaign structure mixing high and low margin products
When multiple products with different margins share a campaign, the campaign's ACoS becomes an average that hides what is actually happening. A high-margin product subsidizing a low-margin one looks fine at the campaign level until you break it down by ASIN.
Separate products with meaningfully different margins into their own campaigns so you can set accurate ACoS targets per product, not per campaign.
A systematic approach to fixing ACoS
Do not try to fix everything at once. Pick the lever with the most impact and work through it completely before moving to the next.
Week 1: Audit search terms. Add 20-30 high-spend, zero-conversion terms as negatives across your top-spending campaigns. Run the search term report filtered by spend descending, look for anything with more than 3 clicks and zero orders.
Week 2: Check budget pacing. For any campaign regularly hitting budget cap before 5pm, set a budget rule or dayparting schedule that reserves more budget for afternoon hours. Off Hours budget rules let you set this automatically.
Week 3: Review placement performance. For any campaign with top-of-search ACoS more than 15 points higher than product page ACoS, reduce the top-of-search bid modifier and reallocate to campaigns performing well at product pages.
Week 4: Review campaign structure. Identify any campaign mixing products with more than 20 points of margin difference. Split them into separate campaigns with accurate ACoS targets.
After four weeks, pull the full-period comparison. Most sellers running this process see 10-20 point ACoS reductions on their worst-performing campaigns within the first 30 days.
What ACoS optimization cannot fix
ACoS is an advertising metric. If your listing quality is poor, weak images, thin bullet points, no reviews, advertising will surface your product to more shoppers and most of them will not convert. High ACoS caused by poor listing quality looks identical to high ACoS caused by bad keyword targeting until you investigate.
Before cutting bids aggressively, confirm your conversion rate on the best-performing keywords is within a normal range for your category. If conversion rate is below 5 percent for a category where 10-15 percent is normal, the listing is the problem, not the campaigns.
ACoS optimization is a continuous process, not a one-time fix. The sellers with consistently strong ACoS are the ones who treat it as a weekly practice: review search terms, check budget pacing, verify placement performance, confirm campaign structure is still logical. Each of those tasks takes 20-30 minutes with the right tools. Done consistently, they compound into a meaningfully more efficient account.
Off Hours helps Amazon sellers and agencies control when their campaigns run and how their budgets are paced. Start a 14-day free trial, no credit card required.