Flow Rate: Definition, Calculation, and Thresholds

The sell-through rate is the percentage of inventory received that has been sold over a given period. It is calculated by dividing the number of units sold by the number of units received, then multiplying by 100: 240 units sold out of 400 received results in a rate of 60%. It is the key metric for products with a short shelf life, such as a clothing collection or a seasonal product, because it indicates whether the purchased inventory is selling at the rate needed to be sold out before the end of the season.

The basic formula is: turnover rate = units sold during the period ÷ units received × 100. This can be tracked on a weekly basis or as a cumulative total since the start of the season. There is also a value-based version, which compares sales revenue to the value of inventory received at the initial selling price: this figure decreases as soon as markdowns are applied. Some retailers divide sales by available inventory (opening inventory plus new arrivals). All these methods are equally valid, provided the same method is used when comparing two products or two seasons.

There is no universal threshold. A good sales rate depends on the product’s shelf life, the time of year, and the cost of unsold inventory. A fashion item with a twenty-week season must be almost entirely sold by the deadline; a permanent item that is restocked weekly should not be evaluated using this metric. Best practice is to set a target sales curve by seasonal milestone at the time of purchase, and then compare the actual rate to this target each week rather than to a market average.

The sales rate assesses a specific batch: what percentage of what was received has been sold. Inventory turnover assesses inventory over time: how many times it is replenished over a period, calculated by dividing the cost of goods sold by the average inventory. The first is used primarily for collections and seasonal products, which are purchased in a single batch and must be sold by a deadline. The latter is used for the permanent product line and cash flow management. Both are complemented by inventory coverage, which estimates how many weeks the current inventory will last.

"Sell-through" is the English term for sales volume: the sell-through rate is the rate at which products are sold. It should not be confused with "sell-in," which refers to sales from the supplier to the distributor, nor with "sell-out," which refers to sales from the distributor to the end consumer. Sell-through bridges the two: it measures what percentage of the merchandise delivered to the retail location has actually been sold. Brands monitor it closely, because high sell-in combined with low sell-through signals returns, markdowns, or reduced orders for the following season.

Start by identifying the cause before lowering the price. The product may be poorly displayed, out of stock in some stores, too expensive compared to competitors, or simply oversold. If the price is the issue, a moderate initial price reduction, applied early on, generally moves inventory more effectively and costs less in terms of profit margin than a steep discount at the end of the season. Next, measure the effect of this price reduction at the next milestone and make adjustments. Simulating the impact of a price cut on sales volume—based on the product’s price elasticity—helps avoid marking down more than necessary.

A very high sales rate early in the season often indicates that a product was under-purchased. Inventory runs out before the expected date; the out-of-stock situation deprives the retailer of sales that aren’t recorded in any report, and customers turn to a competitor. It also suggests that the price may have been too low: some of the units could have been sold at a higher price. The right course of action is to check whether restocking is possible, adjust the quantities ordered for the following season, and, if necessary, revise the selling price of the most popular items.

For seasonal products, weekly monitoring is standard practice: this is the frequency at which adjustments can still be made to pricing, display, or transfers between stores. The first few weeks after a product is placed on the shelves are the most informative, as they quickly reveal which items were over- or under-purchased. An end-of-season review complements this monitoring: it is used to adjust purchase quantities and the target sales curve for the following season. For permanent products, monthly monitoring of turnover and inventory levels is more appropriate.