Sell-Through Rate: Formula and Worked Examples

A 600-unit autumn buy is 31.7% sold at four weeks and 88% sold at twelve. Same buy, same units, same store. Both are sell-through rates and both are correct, which is why a sell-through number quoted without its period is not a number at all.

Sell-through is the metric that grades a single buying decision. Turnover grades the store; sell-through grades what you ordered in March. That makes it the number a buyer actually watches during a season, and it is covered at summary depth in the Shopify inventory metrics guide, which this post sits underneath. Here is the calculation, the ambiguities in it, and how to run it week by week on a real buy.

What sell-through measures

Sell-through is the share of a defined quantity of stock that sold within a defined window. Both definitions have to be stated for the number to mean anything: which units, and over which weeks.

The reason it exists alongside turnover is that a buyer commits to a quantity once and then lives with it. The question during the season is not how fast the store as a whole is moving. It is whether this specific buy is on a pace that clears at full price, and if not, whether there is still time to do something about it.

The formula

Sell-through % = units sold in the period ÷ units available at the start of the period × 100

Shopify's own admin reports a version of this. Its "Products by percentage sold" metric is defined as the "percentage of the product variant sold during the selected period, out of the total starting quantity (values greater than 100%, lower than 0%, or N/A are possible)", per Shopify's inventory reports documentation.

That parenthetical is worth reading twice, because it is the honest part. Sell-through is not a tidy 0 to 100 measure:

Which leads to the competing convention. "Available" has two readings, and both are used in practice:

Starting quantity only. What Shopify's report uses. Correct when the whole buy is on the shelf on day one, and the version to use if you want your number to match the admin.

Starting quantity plus everything received during the period. What a buyer normally means when grading a buy that lands in two or three drops. It keeps the denominator equal to the size of the commitment rather than to whatever happened to be in the building on the first Monday.

If the buy arrives all at once, the two agree. If it does not, they can diverge wildly, and the receipts-inclusive version is the one that answers "did I buy the right amount". State which you used, every time.

Choosing the period

The period does more to the answer than the formula does. Two traps recur.

The first is length. A buy measured at four weeks and the same buy measured at twelve weeks produce numbers that look like they describe different products. Neither is wrong; a rate quoted without its window is just unfinished.

The second is subtler and flatters a stalling buy. Measure sell-through over a trailing window instead of over the life of the buy, and the denominator shrinks as the buy sells down. Weeks nine to twelve of the example below moved 103 units against 175 on hand at the start of week nine, which reads as 58.9%. The buy at that point was actually running out of steam, and the trailing window hid it because the units already sold had left the denominator.

Worked example

Illustrative figures throughout, built to be checkable rather than measured from any real store. A 600-unit autumn buy of "Cedar & Fig, 250g", ordered for a twelve-week season, all of it received before week one. Units sold by week ran 40, 45, 50, 55, 60, 65, 60, 50, 40, 30, 20 and 13.

The arithmetic: 190 ÷ 600 = 31.7%. 425 ÷ 600 = 70.8%. 528 ÷ 600 = 88.0%, leaving 72 units to clear or carry.

Sell-through vs. turnover

Same store, different questions, and the difference lives entirely in the denominator.

Sell-through divides by the units you committed to at the start of a window. It counts one decision. Inventory turnover divides cost of goods sold by average inventory across a period, so every reorder inside that period lands in the denominator. It counts a policy.

The practical consequence: a SKU you reorder continuously will show a healthy turnover and a strange-looking sell-through, because the receipts keep resetting what "available" means. Sell-through earns its keep on buys with a start and an end. Seasonal ranges, launches, limited runs, anything you are not planning to reorder on a rolling basis.

Stock-to-sales ratio

The stock-to-sales ratio is the same relationship inverted, and it comes from department-store merchandise planning, where it feeds open-to-buy.

Stock-to-sales ratio = stock value at the beginning of the period ÷ sales value for the period

It is conventionally monthly. Cedar & Fig starting a month with 240 units at $18 retail is $4,320 of stock; a month of sales at 5 units a day is 150 units, or $2,700. That is a ratio of 1.6, meaning you held 1.6 months of stock going into the month.

Because it is the reciprocal of turnover for the same period, 1.6 implies roughly 7.5 turns a year (12 ÷ 1.6), not 1.6. Note also that it uses beginning-of-month stock rather than an average, which on a SKU that cycles between a reorder point and a target level sits above the average and therefore understates turns. That is the same denominator problem the turnover post works through in detail.

Using it on a seasonal buy

The point of tracking cumulative sell-through weekly is that it turns into a decision while the decision is still available. Two rules of thumb, both about slope rather than level:

If cumulative sell-through is running ahead of the pace needed to clear the buy by the end of the season, and there is enough season left for a reorder to arrive and sell, the number is telling you to place one. That depends on your lead time, not on the rate itself: a 12-day lead time in week eight of a twelve-week season leaves roughly two weeks of selling for whatever arrives.

If the curve is flattening below pace, you are choosing between a markdown now at a smaller discount or a bigger one later on fewer weeks. The 72 units left in the example are the size of that decision. How to run it without gutting margin is covered in selling excess inventory without margin loss, and calculating excess inventory gives you the unit count to work from. If a SKU flattens like this every season rather than once, it has stopped being a seasonal buy problem and become a slow-moving inventory problem.

Sizing the next season's buy is a different job again, and it starts from a seasonal index rather than from last season's sell-through alone. Seasonal inventory forecasting covers that.

None of this is hard to calculate once. It is hard to calculate every Monday for eleven weeks, which is where it usually stops. StockCue forecasts with seasonality on every plan including Free, reading up to 24 months of your order history, so the demand side of a seasonal buy is not a manual export each week.

Frequently Asked Questions

What is a good sell-through rate?

There is no published benchmark worth using, because sell-through depends on how long the season is, how deep the buy was, and when you plan to mark down. A twelve-week buy and a four-week drop cannot share a target. The comparison that works is against your own past buys at the same point in their life: week four of this buy against week four of the last three. The second useful comparison is across your own categories in the same period, which holds your pricing and marketing constant.

Is sell-through the same as inventory turnover?

No, and the difference is the denominator. Sell-through divides units sold by the units you had available at the start of a defined period, so it grades one buying decision. Turnover divides cost of goods sold by average inventory across a period, so it grades a whole store or category over time. A buy can show strong sell-through and still sit inside a store with poor turnover, because turnover counts every reorder you made and sell-through counts one.

What period should I measure sell-through over?

Match it to the life of the buy, then also track it at fixed checkpoints inside that life. A seasonal buy meant to clear in twelve weeks should be measured at twelve weeks, but the useful management number is the cumulative rate at week four and week eight, while there is still time to reorder or mark down. Quoting a rate without naming its period is the single most common way this metric gets misread.

What is the stock-to-sales ratio?

Stock-to-sales is the stock value at the beginning of a period divided by the sales value for that period, conventionally calculated monthly in retail merchandise planning. It is the reciprocal of turnover for the same period, so a monthly stock-to-sales ratio of 4 implies roughly three turns a year, not four. It answers the same question as sell-through from the other direction: how many months of stock you were holding rather than what share of it you sold.