Two stores can have the same budget and the same brand, and one sells out at full price while the other drowns in markdowns. The difference is usually the assortment: what was on the rails, in what breadth and depth, for that store's customers.
Assortment planning is the discipline behind that mix. This guide covers what it is, the breadth-versus-depth trade-off at its heart, how the process works, and why it is unusually hard, and unusually valuable, in fashion. It is the product-level companion to merchandise planning.
What is assortment planning?
Assortment planning is the process of deciding which products to offer, and in what quantities of variety, for each store, channel, and season. Where merchandise planning sets the financial plan, the budget, the sales and margin targets, assortment planning turns that money into an actual range of styles, colors, and sizes.
Put simply: merchandise planning decides how much you can spend; assortment planning decides what you buy with it. A plan can be financially perfect and still fail if the assortment is wrong, too broad, too shallow, or badly matched to the customer in front of it.
It is also where most of a season's margin is won or lost. The assortment sets the ceiling on full-price sales and the floor on markdowns before a single item is even bought, which is why it deserves at least as much rigor and attention as the financial plan sitting above it.
Breadth vs depth: the trade-off at the heart of assortment
Every assortment decision comes back to one tension: breadth versus depth. It is the first thing to get right and the easiest to get wrong.
- Breadth (or width): how many different categories or product types you carry. A department store is broad: many categories, fewer choices in each.
- Depth: how many options you offer within a category, the styles, colors, and sizes. A specialist sneaker shop is deep: one category, dozens of variations.
Neither is right in the absolute; the balance depends on the customer and the format. A broad, shallow assortment covers many needs but risks feeling generic and holding little of anything. A narrow, deep assortment signals authority in its category but bets heavily on that category staying in demand. Most retailers sit somewhere between, and the skill is knowing where.
The assortment planning process
However it is dressed up, the process follows a consistent sequence, working from the financial plan down to individual options.
- Analyze last season: which categories, styles, and price points sold through, and which were marked down.
- Cluster stores and channels by demand, so the plan can flex rather than treat every location the same.
- Set the category structure: the breadth of categories and the target share of the budget for each.
- Plan the depth: the number of options, and the size and color breakdown, within each category.
- Reconcile with the budget and open-to-buy, so the range fits the money available.
- Track sell-through in-season and adjust: repeat winners, exit slow options before they need markdown.
Store clustering and localization
A national assortment sent identically to every store is the most common and most expensive assortment mistake. Demand is local; the plan should be too.
Clustering groups stores by shared characteristics, sales volume, climate, demographics, or space, so each cluster gets an assortment sized and shaped to its demand. A flagship in a major city and a small regional store should not carry the same breadth or depth, and a warm-climate store should not receive the same seasonal mix as a cold one.
The same logic now extends across channels. Online can carry a far broader assortment than any physical store, because it is not constrained by shelf space, which reshapes what each channel should hold.
Core, fashion, and seasonal: the fashion mix
Fashion assortments carry a mix of very different products, and treating them the same is a recipe for markdowns. The fashion cycle moves each part at a different speed.
- Core (or carryover): the reliable basics that sell year-round. They can be planned deep and replenished, with low trend risk.
- Fashion: the trend-led pieces that define a season but date fast. They are planned shallower and bought closer to season, because the downside of over-buying is severe.
- Seasonal: products tied to a specific window, from coats to swimwear, where timing the entry and exit is everything.
- The newness ratio: the split between new options and repeated carryover each season. Too much newness raises trend risk and cost; too little makes the range feel stale.
On top of this sits price architecture, often called good-better-best: a deliberate spread of entry, mid, and premium price points so the assortment has an opening price to pull customers in and a top price to trade them up. The number of options at each level is a core assortment decision.
The metrics of a good assortment
Assortment quality is measured, not guessed. These are the numbers, the fashion analytics that tell you whether the mix is working.
- Option count: the number of distinct choices in the range; too many dilutes focus and inventory, too few loses sales.
- Sell-through by option: which specific styles, colors, and sizes actually sold, the sharpest read on assortment quality.
- SKU productivity: sales and margin per option, so weak options can be cut and strong ones extended.
- Size and color effectiveness: whether the depth was spread across the right sizes and colors, or wasted on the wrong ones.
Common assortment planning mistakes
The same errors recur, and most come from planning the mix in a spreadsheet detached from real demand.
- One assortment for every store: ignoring local demand and clustering, so some stores starve while others overstock.
- Too broad, too thin: chasing variety until the range holds a little of everything and not enough of anything.
- Over-depth on fashion: buying trend pieces as if they were core, then discounting the excess.
- Ignoring returns: planning on gross demand and being caught out when poor fit or wrong color drives products back.
- Planning off history alone: building next season's mix from last season's sales, in a market that has already moved.
From mix to signal: better assortments need better demand data
Every technique here depends on one input: a view of what customers will actually want, by product, by location, next season. That demand signal is where most assortment plans are weakest.
Traditional assortment planning leans on last season's sales and a buyer's instinct. But demand is shaped by forces that never show up in a sales report, weather, culture, the economy, and emerging trends. Reading those signals is what turns raw fashion analytics into fashion intelligence you can plan an assortment against.
This is the layer apshan builds: a connected, sourced signal layer that helps you shape the mix, which categories to widen, which options to deepen, which trends to back, on more than history and instinct. Request access or see the plans and pricing.
The payoff is concrete: a mix shaped by a richer view of demand widens the categories that will actually sell, deepens the options customers will actually want, and quietly shrinks the markdowns that quietly eat away the whole season's margin.