The idea in one line. Sell-through tells you whether the buy was right. Weeks of cover tells you how long you can afford to wait to find out. Together they run the shop floor.
Definitions. SELL-THROUGH (ST%) = units sold ÷ units received, over a defined period — a week, a month, a season. FULL-PRICE ST% counts only units sold before the first markdown; this is the honest version, because it measures whether the customer wanted the product at the price you believed in. WEEKS OF COVER (WOC) = units on hand ÷ average weekly sales — how many weeks the current stock lasts at the current pace.
Why it matters. A buyer who looks only at revenue sees a shop that "sells". ST% shows what share of the risk you took has paid off; WOC shows where cash is trapped. A style at 80% full-price sell-through after eight weeks is a reorder candidate. A style at 20% with thirty weeks of cover is a markdown waiting to happen. Both can show the same revenue this week.
Reading the numbers. Benchmarks depend on category and business model — fast fashion expects high sell-through within weeks, luxury accepts lower sell-through over a long season and protects the price — so treat any single target as a rule to calibrate, never a law. What is universal: ST% is read by week of life, never in isolation. 40% in week three is strong; 40% in week fourteen is a problem.
The two mistakes. Counting sell-through after markdown as success — you cleared stock, you did not sell the product. And ignoring WOC because a style "is selling": five units a week with four hundred on hand is eighty weeks deep in a twenty-week season.
The bridge. Sell-through is the outcome side of your Source Card. The trend call said "this silhouette will land"; the full-price ST% eight weeks later is the verdict. Merchandisers who record both build their own forecasting skill — the only kind no bureau can sell you.
Practice. Take any style with units received, weekly sales and units on hand. Compute ST% (total and full-price) and WOC, then write one line: reorder, hold, or mark down — and why. If you cannot decide, you are missing the week of life.