What is WSSI? Weekly sales, stock & intake planning

Anyone who's worked in fashion or apparel merchandise planning knows the WSSI. It's often pronounced "wizzy" and treated as the single source of truth for whether a category is on plan. It's the spreadsheet (or system) everyone opens on a Monday to see where sales, stock, and buying stand. And outside that world, almost nobody has heard of it.

This article explains what WSSI is, the components that make it up, what it's actually used for, and — the part that matters most — where it stops. Because WSSI is an excellent planning frame, and a planning frame is not the same thing as the decisions that fill it.

What WSSI is

WSSI stands for Weekly Sales, Stock and Intake. It's a merchandise planning report that forecasts and tracks a category's inventory, week by week, across a season. At its simplest, it answers one question on a weekly cadence: given the sales plan, how much stock should we hold, and how much can we still buy?

It's typically built by category, department, or division — not by SKU — and expressed in value (at cost or retail) as often as in units. It runs across a season (spring/summer, autumn/winter) at weekly granularity, which is where the "weekly" in the name comes from. The merchandiser or planner owns it, updates it, and re-plans it as actual sales come in.

In short, WSSI is the top-down financial heartbeat of merchandise planning. It sits alongside the broader discipline of merchandise financial planning — WSSI is the weekly, operational face of it.

The components of a WSSI

A WSSI is a small set of lines that connect into one weekly balance. Five make up the core.

Opening stock is what a category holds at the start of the week. Sales are the week's planned, then actual, sales, at value or units. Markdown is the value taken out of stock through price reductions.

Intake is the goods received into stock that week — deliveries and receipts. And closing stock is what's left at the end: opening stock plus intake, minus sales and markdown.

From these, a WSSI derives two numbers that make it powerful. Weeks' cover — closing stock divided by the rate of sale, i.e. how many weeks the current stock would last. And open-to-buy (OTB) — how much budget is left to spend on future intake, given the sales and stock plan. OTB is the guardrail: it stops a category from over-buying into overstock or under-buying into stockouts.

The lines are simple; the value is in the loop. Each week, actuals replace the plan, the merchandiser re-plans the rest of the season, and the OTB updates. A WSSI is a living document, not a static budget — which is exactly why it's the report merchandisers live in.

What WSSI is used for

A WSSI exists to control inventory investment against the sales plan — and it does three jobs to get there.

Managing open-to-buy. This is the headline use. WSSI tells a merchandiser how much they can still commit to buy without breaking the stock plan, week by week. It's the financial discipline that keeps a season from ending in either overstock or empty shelves.

In-season control and re-planning. As actual sales diverge from plan — and they always do — the WSSI is where a category is re-steered. Sell ahead of plan and cover drops, so you bring intake forward; sell behind and cover balloons, bringing markdown or reduced intake into view. This is the same tension that plays out in inventory planning more broadly.

A shared source of truth. Because finance, buying, and merchandising all read the same WSSI, it aligns them on one set of numbers — the plan everyone is steering toward. That alignment is worth a lot on its own.

Done well, WSSI keeps a category financially healthy through a season. But notice what all three jobs have in common: they operate on aggregates — category, value, week. And that's where the limit begins.

Where WSSI stops: the plan vs the decisions

Here's the honest boundary. A WSSI is a top-down plan at the level of category, value, and week. The business, however, runs on bottom-up decisions at the level of SKU, store, and day.

WSSI tells you a category should hold four weeks' cover and has £80k of open-to-buy left. It does not tell you which SKUs to reorder, to which stores, in what quantity, or which slow lines to transfer or mark down first. Those are thousands of decisions the plan frames but doesn't make — and in most retailers they're still made by hand, in separate spreadsheets, or in the weekly trade meeting. A forecast carrying 30% error at the SKU/store level doesn't get more decidable because the category-level WSSI is on plan.

This is the same gap that sits under replenishment, under allocation, under a retail ERP versus a decision layer. The planning system sets the frame, and something else has to make the granular calls inside it. WSSI is a superb frame. It was never designed to be the decision engine — and treating it as one is why so much merchandise data stays a plan nobody can execute at scale.

The Solya angle

This is the layer Solya adds beneath the WSSI: not a replacement for the plan, but the engine that executes the decisions inside it.

Solya connects to your ERP, POS, and supply chain systems and rebuilds a live SKU/store view of the network on the data layer. The WSSI sets the frame — the sales plan, the cover targets, the open-to-buy. The intelligence layer makes the granular calls that respect it: which SKUs to reorder to which stores, what to transfer, what to mark down, all against your business rules. The orchestration layer then pushes those cleared decisions into execution, so the WSSI's intent becomes purchase orders and transfers without a planner keying them SKU by SKU. That's continuous replenishment operating inside the financial guardrails the WSSI defines.

The point is complementarity, not replacement. Keep your WSSI — it's the right tool for planning the money. Add the decision layer that turns that weekly plan into thousands of executed SKU/store moves, so the plan and the reality finally match.

The bottom line

WSSI — weekly sales, stock and intake — is the weekly heartbeat of merchandise planning: the report that controls inventory investment and open-to-buy against a category's sales plan. Every serious merchandise operation needs one, and a good WSSI is genuinely valuable.

But a WSSI plans; it doesn't decide. It sets the category-level frame in value and weeks, and leaves the SKU/store/day decisions to be made underneath it. The retailers that pull ahead keep the WSSI for what it's great at. And they add the decision layer that executes inside it, at the granularity the business actually runs at.

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Is your WSSI ahead of the decisions that execute it?

At Solya, we offer retail merchandising and supply chain leaders a 30-minute diagnostic. It assesses, on your own categories, where your WSSI plan is sound but the SKU/store decisions underneath it lag. You'll walk away with:

• A read on where the plan is on track but the granular decisions aren't executed in time
• The SKU/store decision loops leaking margin inside a healthy-looking WSSI
• The first loops worth closing to make the weekly plan true on the floor