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Anyone running an FBA business knows the inventory problem: too much stock creates storage costs and aged inventory pressure, while too little creates stockouts and missed sales.
That tension hasn't changed since 2018. What changed is how Amazon measures it.
Today's FBA sellers need to read four signals at once: sell-through rate, historical days of supply, days of cover, and aging risk. Amazon added the low-inventory-level fee in 2024. The Inventory Performance Index ties your storage capacity to how well you balance those metrics. And parent-level tracking matters for variation families in ways that weren't true before.
Same problem. New scoreboard.
This guide explains what Amazon sell-through rate is, how the 90-day FBA formula works, where to find it in Seller Central, what a good number looks like, and what to do when the numbers say restock, sell down, or something in between.
What Is Amazon Sell-Through Rate?
Sell-through rate is the ratio of units sold to inventory available over a period.
Retail businesses use it to measure how fast inventory moves. A store with 100 units that sells 50 in a month has a 50% sell-through rate.
Amazon's FBA sell-through rate uses a different formula. Instead of a percentage, Amazon calculates a ratio: units shipped over the past 90 days divided by average FBA inventory on hand during that same period.
Example: A product shipped 270 units over 90 days. Average inventory on hand during that period was 90 units.
FBA sell-through rate: 270 ÷ 90 = 3.0
That 3.0 tells you that for every unit sitting in FBA inventory, you shipped three units over the past 90 days.
Amazon uses this number inside the Inventory Performance Dashboard and the FBA Inventory tool. It's one of the four factors that affect your Inventory Performance Index (IPI) score.
Sell-through rate is not the same as sales velocity. Sales velocity is units sold per day or per week. Sell-through rate is a ratio of sales to stock on hand.
Sell-through rate is not the same as days of cover. Days of cover tells you how many days of inventory you have left at current sales velocity. Sell-through rate tells you how many times your inventory turned over relative to what you kept in stock.
Sell-through rate is not the same as inventory turnover. Inventory turnover (COGS ÷ average inventory value) is an annual financial metric. Sell-through rate is a 90-day operational metric Amazon uses to decide whether your inventory balance is healthy.
They're related. They're not interchangeable.
Where to Find FBA Sell-Through Rate in Seller Central
Go to Inventory → Inventory Performance.
Scroll to the FBA Inventory section.
Click View Details to open the FBA Inventory tool.
Look for the Sell-through rate column.
You'll also see historical days of supply in the same view. That metric matters for the low-inventory-level fee (more on that below).
Amazon's FBA Inventory tool replaced older workflows centered on the "Inventory In Stock" report. If you're still using that older report, the navigation and metric names have changed.
What Amazon Considers a Good Sell-Through Rate
Amazon's FBA education materials describe a benchmark scale:
| Sell-Through Rate | Rating |
|---|---|
| 3 to 7 | Good |
| 1 to 2 | Fair |
| Below 1 | Poor |
A rate above 3 means you're moving inventory faster than you're holding it. That's what Amazon wants to see.
A rate below 1 means you're holding more inventory than you're moving. That creates excess inventory, increases storage costs, and drags down your IPI score.
But context matters.
A high sell-through rate looks good on the dashboard, but if you only have 10 days of cover left and your supplier lead time is 30 days, you're heading toward a stockout.
A low sell-through rate looks bad, but if the product is seasonal and you're stocking ahead of Q4, the number might be fine for now.
The benchmark gives you a starting point. The rest of your inventory data tells you whether the number is actually a problem.
Sell-Through Rate and Your IPI Score
Your Inventory Performance Index (IPI) is a 0–1,000 score that Amazon uses to decide how much FBA storage capacity you get.
IPI is based on four factors:
- Excess inventory (more than 90 days of supply)
- Sell-through rate
- Stranded inventory (listings with stock but no active offer)
- In-stock rate (how often you have inventory available on FBA-eligible ASINs)
A poor sell-through rate drags your IPI score down. A low IPI score (below 400 in recent years) can result in reduced FBA storage capacity and restock limits.
Low sell-through rate → low IPI → reduced capacity → stockouts.
That's the loop FBA sellers need to avoid.
The Real Cost of Slow-Moving Inventory
Slow-moving inventory creates three cost layers:
1. Monthly storage fees
Amazon charges per cubic foot per month. As of 2026, standard-size storage fees range from $0.78 to $2.40 per cubic foot depending on time of year.
2. Aged inventory surcharge
Amazon charges escalating surcharges on inventory stored longer than 181 days:
- 181–270 days: first tier
- 271–365 days: second tier
- 12–15 months: $0.30/unit or $6.90/ft³
- 15+ months: $0.35/unit or $7.90/ft³
The longer inventory sits, the more those fees stack.
3. Opportunity cost
Inventory that doesn't move ties up cash you could use to restock faster sellers or test new products.
Industry estimates put annual carrying cost at 20% to 30% of inventory value. That includes storage, insurance, obsolescence, and capital cost.
For FBA sellers, aged inventory surcharges and IPI penalties make that number worse.
The Two-Sided Risk: Too Much vs. Too Little Inventory
The 2018 version of this article focused on overstock risk. That's only half the story now.
Too much inventory creates:
- Monthly storage fees
- Aged inventory surcharges
- Excess inventory flags that lower IPI
- Cash-flow pressure
Too little inventory creates:
- Stockouts
- Lost sales
- Lower in-stock performance (which also affects IPI)
- Potential low-inventory-level fee exposure
Amazon added the low-inventory-level fee in 2024. It applies to standard-size products when both the short-term (30-day) and long-term (90-day) historical days of supply metrics fall below 28 days.
Amazon calculates historical days of supply at the parent-product level for variation families. That means one slow-moving child ASIN can't offset the fee if the parent-level aggregate is below the threshold.
The fee structure varies by size tier and shipping weight. Check Amazon's current rate card for your specific products.
The balancing act: You need enough inventory to avoid stockouts and low-inventory-level fees, but not so much that you create aging risk and excess-inventory flags.
Sell-through rate alone doesn't tell you which side of that line you're on. You need to read it alongside historical days of supply, days of cover, and current inventory levels.
How to Improve Your Amazon Sell-Through Rate
If your sell-through rate is below Amazon's "good" range, here's what to check:
1. Tighten demand forecasting and replenishment cycles
Review your sales velocity over 30, 60, and 90 days. If you're overstocking based on outdated sales assumptions, adjust your reorder quantities and safety stock calculations.
2. Improve listings to increase conversion
Better images, tighter copy, A+ content, and updated product details can lift conversion rates without changing inventory levels. Higher conversion means faster sell-through.
3. Use advertising to accelerate slow movers
Sponsored Products and Sponsored Brands can move inventory faster. If a product has decent margin and you need to clear stock before aging fees hit, advertising can pay for itself.
4. Adjust pricing strategically
A 5% to 10% price reduction on slow-moving inventory can increase velocity enough to avoid aged inventory surcharges. Run the math: does the margin loss beat the fee exposure?
5. Create removal orders or use Amazon's liquidation program
If inventory won't move at any reasonable price, removing it before aging fees stack is the better choice. Amazon offers a liquidation program that recovers some value instead of paying removal fees.
6. Bundle slow-moving products with faster sellers
If you have multiple SKUs, bundling a slow mover with a hero product can increase velocity on both. This works best when the bundle makes sense to the customer.
Using Amazon's Inventory Reports for Proactive Management
Amazon's FBA Inventory tool gives you product-level visibility into:
- Sell-through rate
- Historical days of supply (30-day and 90-day)
- Excess inventory flags
- Aging risk
- Restock recommendations
Set up a weekly cadence to review:
Low sell-through + high days of cover: Sell down or cut exposure.
High sell-through + low days of supply: Replenish faster or adjust inbound timing.
Decent sell-through + aging inventory: Clear old units before surcharges stack.
Parent-level low days of supply: Check variation families for low-inventory-level fee risk.
The Inventory Performance Dashboard gives you account-level health at a glance. Use it to track your IPI score, excess inventory percentage, and in-stock performance.
If you see your IPI score dropping, sell-through rate is one of the four levers you can pull to fix it.
Real Scenarios and What to Do
Scenario 1: Runaway best-seller
Your product has a strong sell-through rate, but inbound lead time is 25 days and current historical days of supply is slipping under 28.
Risk: Stockout plus low-inventory-level fee exposure.
Fix: Expedite the next shipment or increase safety stock to keep days of supply above the threshold.
Scenario 2: Variation-family trap
One parent ASIN has fast-selling child variants and slow-moving child variants. Sell-through looks decent on the hero SKU, but parent-level historical days of supply is flagged.
Risk: Low-inventory-level fee at the parent level.
Fix: Increase stock on fast movers or reduce stock on slow movers to bring the parent-level aggregate above 28 days.
Scenario 3: False "healthy" STR
Your 90-day sell-through rate is 4.5 (good), but you only have 12 days of cover left.
Risk: Imminent stockout.
Fix: Reorder now. Strong sell-through doesn't remove replenishment risk.
Scenario 4: Slow-SKU margin drain
A product has a sell-through rate of 0.8 and more than 90 days of supply. Monthly storage fees and aged-inventory charges are eroding margin.
Risk: Fee exposure that turns a profitable SKU into a loss.
Fix: Advertise, discount, bundle, or remove before aging surcharges stack further.
Scenario 5: Seasonal demand spike
A seasonal item shows low days of supply in the short-term view but healthier numbers over 90 days.
Interpretation: Amazon checks both short-term and long-term demand windows for low-inventory-level fees. If both fall below 28 days, the fee applies.
Fix: Stock ahead of seasonal spikes or use Amazon Warehousing and Distribution (AWD) as reserve inventory.
Scenario 6: Reserve-stock strategy
You keep a tighter FBA position and hold reserve inventory in AWD or a 3PL.
Benefit: Lower FBA storage costs and aging risk.
Tradeoff: Tighter days of supply and more active inventory planning to avoid stockouts.
How SupplyKick Manages FBA Inventory for Brands
At SupplyKick, we manage FBA inventory as part of our full-service Amazon management. We run demand forecasting, set reorder points that balance cost and stockout risk, monitor IPI and sell-through metrics, and absorb FBA fees as part of the engagement.
That means we own the outcome: keeping your hero products in stock, avoiding aged inventory surcharges, and maintaining healthy IPI scores so your account keeps full storage capacity.
If you're managing inventory yourself and the balancing act is eating time you'd rather spend on product development or marketing, talk to us.
Let SupplyKick Handle Your Amazon Inventory
We manage sell-through, IPI scores, and storage costs so you can focus on growing your brand.
Connect With Our TeamFAQ
What is a good sell-through rate on Amazon?
Amazon considers a sell-through rate of 3 to 7 as "good." A rate of 1 to 2 is "fair," and anything below 1 is "poor." Higher rates indicate healthy inventory turnover and contribute to a stronger IPI score.
How does Amazon calculate FBA sell-through rate?
Amazon divides the total units shipped over the past 90 days by the average number of units available at fulfillment centers during that same period. This is different from a simple percentage calculation.
How does sell-through rate affect my IPI score?
Sell-through rate is one of four factors in Amazon's Inventory Performance Index. A poor sell-through rate drags down your IPI score, which can result in reduced FBA storage capacity and restock limits.
What is the aged inventory surcharge on Amazon?
Amazon charges escalating surcharges on FBA inventory stored longer than 181 days. Rates increase at 271 days, 365 days, and again at 15+ months. Maintaining a healthy sell-through rate is the primary way to avoid these fees.
What is historical days of supply and why does it matter?
Historical days of supply measures how many days of inventory you have on hand based on recent sales velocity. Amazon uses both 30-day and 90-day windows. If both fall below 28 days, standard-size products may be subject to the low-inventory-level fee.
Does Amazon calculate low-inventory-level fee exposure at the child-SKU level or parent level?
Amazon calculates it at the parent-product level for variation families. That means you need to look at the aggregate inventory position across all child ASINs, not individual SKUs.
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