Sell-through rate: formula, Amazon's FBA version and common mistakes

Sell-through rate answers a blunt question: of the stock you brought in, how much did customers buy? It shows whether a purchase order matched demand.

How do you calculate sell-through rate?

Amazon's seller guidance and SPS Commerce use the same formula:

Sell-through rate = units sold ÷ units received × 100

Keep both numbers on the same SKU, location and period. Shopify notes the rate is often calculated monthly, and SPS Commerce recommends tracking it monthly; weekly or quarterly also works if it matches how you buy.

Shopify's formula divides by stock on hand, which it describes as all the stock available for sale that month, although its definition and worked example use units received. Read literally, for a SKU that carries stock from month to month, that denominator is opening stock plus receipts, and the answer changes. Take one SKU in one month with 200 units of opening stock, 800 received and 700 sold:

Version	Calculation	Result
Units received only (Amazon, SPS Commerce)	700 ÷ 800	87.5%
All stock available for sale (opening + received)	700 ÷ 1,000	70%

Pick one version and use it for every SKU.

How does Amazon measure FBA sell-through?

Amazon presents FBA sell-through as a gauge of how well your FBA stock is balanced and refreshes it daily on a Seller Central dashboard. Its FBA Inventory guide divides the units that sold and reached customers in the last 90 days by the sellable stock you held in its warehouses, averaged across that window. SPS Commerce and Aura describe the same rolling 90-day ratio. It is one of the drivers of the IPI score.

Read it as turns, not a percentage. A SKU that shipped 900 units in 90 days with 450 on hand on average scores 2.0, about 45 days of average cover. By the same arithmetic, 1.0 is about 90 days of average cover. That sits close to the 90 days of supply Amazon's guidance calls excess, but it is a rule of thumb, not Amazon's test. Amazon measures supply against customer demand and also flags any unit aged over 90 days, so a SKU can count as excess with sell-through above 1.0. Amazon suggests holding about two months of supply.

The SP-API also returns a sell-through column in the FBA Manage Inventory Health report (GET_FBA_INVENTORY_PLANNING_DATA), next to units shipped over 7, 30, 60 and 90 days and inventory age buckets. The report can be requested but not scheduled, and it is not offered in the Netherlands, Poland, Sweden or Belgium stores.

Why does sell-through rate matter for operations and growth?

Low sell-through is cash sitting in a warehouse. In the US, FBA units that stay in Amazon's fulfillment centers for 181 days or longer pick up a monthly aged inventory surcharge as well as the monthly storage fee, the gap covered in long-term storage fees. Excess stock and weak sell-through also pull down the IPI score.

High is not automatically good. SPS Commerce and Wall Street Prep both warn that a rate close to 100% can mean you under-ordered and missed sales. On a best seller, that ends as a stockout.

The trend per SKU is the signal. Falling sell-through with steady receipts means the next purchase order should shrink. Rising sell-through with thin days of cover means reorder now or ease off ads.

What mistakes make sell-through misleading?

• Mixing formulas. An 80% monthly retail rate and a 2.0 Amazon 90-day ratio are different units. Never compare them directly.
• Blending channels. One number across Amazon, Shopify and Walmart hides where stock is stuck. Measure per SKU per location.
• Dating receipts wrong. Count units when they become sellable, not when the PO ships, or one late container distorts two months.
• Ignoring stockout days. A SKU that sat at zero for two weeks shows high sell-through because nothing was left to sell.

How does Growth OS track sell-through?

Ecomsellertool Growth OS is built to compute sell-through one consistent way per SKU, location and channel, from data on your own accounts. During deployment, its inventory and reporting modules can be set up for four jobs:

1. Units sold from marketplace order data and units received from FBA, 3PL and warehouse receipts, dated when stock became sellable. A transfer between your own locations counts as a receipt at the location that gets it but stays out of brand-level totals, so no unit is counted twice.
2. Amazon's view from the Manage Inventory Health report, with a fallback calculation from orders and inventory snapshots in stores where the report is not offered.
3. Flags when sell-through falls while units age toward a surcharge band, with price, deal, ad and removal options costed side by side.
4. Purchasing tied to measured sell-through, so replenishment follows real demand.

You own the custom modules we build and your data; the Growth OS base is licensed to you.

Where should you start?

If sell-through lives in a spreadsheet, or nobody can say which SKUs will age into surcharges next month, start with the free Quick Scan in the Ops Gap Diagnostic. It works from five standard Amazon reports you upload and returns your top three operations gaps, each with a yearly dollar estimate. To see the base system first, look at Growth OS.