What sell-through rate means in FBA
Sell-through rate (STR) measures how fast your inventory moves relative to how much you keep on hand. In Amazon’s FBA ecosystem, it is one of the four metrics that directly feeds your Inventory Performance Index (IPI) score. A low sell-through rate signals to Amazon that you are using warehouse space inefficiently.
The concept is straightforward: if you shipped 500 units over 90 days and held an average of 1,000 units during that time, your sell-through rate is 50%. The higher the ratio, the more efficiently you are converting stored inventory into sales.
For FBA sellers, sell-through rate is the clearest signal of inventory health at the SKU level. A SKU with a declining sell-through rate is either losing demand, overstocked, or both. Either way, it needs attention before it drags down your IPI and triggers storage capacity restrictions.
Sell-through rate formula
Example: a $3.2M private label seller
A private label seller running 30 SKUs at $3.2M annual revenue (average selling price $42). Take a mid-range SKU:
- Units shipped in last 90 days: 1,260
- Average daily on-hand inventory over 90 days: 850 units
Sell-through rate = 1,260 ÷ 850 = 1.48
This means the seller turned over roughly 1.5x their average inventory in 90 days. Expressed as a weekly rate: 1,260 ÷ ~13 weeks = about 97 units/week shipped, well above Amazon’s 3-unit/week threshold.
Now compare two SKUs side by side:
| Metric | SKU A (healthy) | SKU B (problem) |
|---|---|---|
| Units shipped (90 days) | 1,260 | 180 |
| Avg on-hand (90 days) | 850 | 1,400 |
| Sell-through rate | 1.48 | 0.13 |
| Weekly units | ~97/week | ~14/week |
SKU B has a sell-through rate of 0.13, meaning it would take over 7 periods (630+ days) to sell through at the current pace. This SKU is dragging down the account’s IPI.
FBA-specific considerations
Sell-through rate in Amazon’s FBA context has important differences from the generic retail definition:
Amazon uses a rolling 90-day window. Unlike retail where sell-through is often calculated over the product’s lifetime or a buying season, Amazon’s version resets continuously. A spike in sales 91 days ago drops out of the calculation. This means your sell-through rate can decline even if total sales are growing, simply because you recently received a large shipment that raised your average on-hand.
Sell-through rate directly affects your IPI score. Of the four IPI inputs (sell-through, excess inventory, stranded inventory, in-stock rate), sell-through rate is the one most within your daily control. You cannot instantly fix stranded inventory or change your in-stock history, but you can run a promotion or create a removal order to move slow units and improve sell-through within weeks.
Shipping to FBA temporarily lowers your rate. When a large inbound shipment checks in, your average on-hand jumps immediately but the sales impact takes weeks to materialize. This creates a predictable dip in sell-through rate after every restock. Plan for it and avoid over-reacting by running unnecessary promotions during the first 2 to 3 weeks after a large check-in.
Common mistakes
- Confusing sell-through rate with inventory turnover ratio. Sell-through rate uses unit volume over a fixed period. Inventory turnover uses cost of goods sold divided by average inventory value over a year. A high sell-through rate does not guarantee high turnover if your COGS is low relative to inventory value.
- Panicking after a restock. A large inbound shipment immediately raises your average on-hand, which drops your sell-through ratio. This is normal and temporary. Wait 3 to 4 weeks for the ratio to stabilize before making adjustments.
- Ignoring the denominator. Many sellers focus only on increasing sales (the numerator) to improve sell-through. But reducing excess on-hand inventory through removal orders or promotion is often faster. Cutting your average on-hand from 1,400 to 700 units doubles your sell-through rate overnight.