The model stock plan: your category's baseline, written down before you buy

Search for "model stock plan" and you'll land on retail buying textbooks from decades ago, not software features. That's the first thing to know about it: this is buying-desk vocabulary — a written document, not a module, and no Shopify admin screen is named after it. The second thing to know: it fills the exact gap between the two decisions every store makes anyway. Assortment planning decides what you carry. Open to buy decides how much money you can spend this month. Neither decides how many of each SKU should be on the shelf — and that missing middle layer is the model stock plan.

The definition, once, in plain English

A model stock plan is a written list of the quantity you intend to hold for each SKU in a category — your planned baseline — built from two inputs: how fast you expect each SKU to sell, and how many weeks of cover you want on the shelf. That's the whole definition. For the rest of this article we'll just call it the baseline.

A related term from the same textbooks: the basic stock list, which some writers reserve for the never-out staples subset — the items you'd hold extra cover on no matter what. In practice, small stores write one document: higher cover targets on staples, lower on seasonal and test items. Whether you label the file "model stock plan" or "stock baseline" matters less than that it exists, dated, before the buying decisions it's meant to referee.

Where it sits: range → baseline → budget

The three documents chain together like this:

1. Range: assortment planning decides the width and depth of what you carry — 12 notebook SKUs, not 9, and no leather covers this season.
2. Baseline: the model stock plan converts that range into quantities — how many units of each of the 12 you aim to hold.
3. Budget: open to buy caps the dollars this month's purchases can consume, given what you already own and have on order.

Without the middle document, the budget conversation happens in the dark: "we can spend $600" has no meaning until you know whether $600 covers the baseline for a category or double-fills it.

The calculation, worked on real numbers

Paper & Co. is a stationery store with 12 notebook SKUs. Staples get a 42-day (six-week) cover target; the limited-run collab notebook gets 21 days because it's a trend item with a short runway. Four representative rows:

The arithmetic, shown once: dot-grid A5 sells 36 a month, so 36 ÷ 30 = 1.2 per day; 1.2 × 42 days = 50.4, rounded up to a baseline of 51 units. Do that per SKU and the five rows above plan $514.80 at cost; run all 12 SKUs and the category baseline lands around $1,240 at cost (illustrative — it depends entirely on your costs and mix).

Two refinements worth adopting early. Use expected sales, not last month's raw number, when you know a season is turning — the baseline is a plan, and the retail buying calendar tells you when expectations should outrun history. And set cover targets by role, not universally: a common starting point is 6–8 weeks for staples, 4–6 for seasonal core, 2–3 for tests and trends. Those are starting points to adjust against your supplier lead times, not rules with an authority behind them.

What the baseline does at the buying desk

The baseline's job is to be the referee for every PO. Example: a purchase order arrives for 120 dot-grid A5 notebooks. Your baseline says 51; you're holding 44. That order implies ending at 164 units — 3.2× the baseline. Either demand has genuinely changed (in which case, update the baseline first and order against the new number) or the order is wrong (a rep's volume suggestion, a miscounted case pack, an old quantity pasted forward). Without a baseline, that PO reads as "a normal order." With one, it reads as an anomaly in five seconds.

It also converts cash questions into unit questions. When money feels tight, the baseline tells you which categories are simply holding more than planned — the overbuy shows up as "23% over baseline" instead of a vague sense of fullness — and the open to buy calculation consumes it directly: baseline value minus on hand minus on order gives the dollars actually available to spend (the OTB mechanics live in the open-to-buy guide; the baseline is an input to them, not a substitute).

Keeping it honest

Baselines rot quietly, so give the document three habits:

• Rewrite it quarterly, alongside the range review. The same session that adds or retires SKUs should re-run the baseline math — a range decision without a quantity update is half a decision.
• Read reality against it weekly. The days-of-cover math is the natural bridge: a SKU at 120 days of cover against a 42-day baseline is overstocked by exactly three baselines' worth, and the number explains itself.
• Park it as a column, not a separate shrine. Most stores keep the baseline as a column in the reorder spreadsheet — target holding next to on hand next to trigger. The reorder sheet's structure is already built for this; the baseline column is what turns "reorder now" into "reorder up to here."

One piece of honesty about tooling: nothing in the Shopify admin is named a model stock plan, and native analysis can rank SKUs for you but won't decide your cover targets. That's not a gap in your stack — it's the nature of the document. It's a judgment layer, and the spreadsheet remains the right home for it longer than most people expect.

Why bother, in the spreadsheet era

Because the baseline is what makes every other inventory number interpretable. "We're at 18 days of cover" is trivia until you know the plan says 42. "This PO looks big" is a feeling until the baseline says it's 3.2× target holding. The classic term survived fifty years of buying desks for one reason: a quantity written down before the buying decision is the only referee that shows up on time. Nothing about that has changed with software.

Common questions

What is a model stock plan in retail? A written list of the quantity you intend to hold for each SKU in a category — the planned baseline — calculated from expected sales rate and a target weeks-of-cover. It's the middle document between assortment planning (what you carry) and open to buy (what you can spend). Classic buying-desk vocabulary, kept in a spreadsheet, not a software feature.

What's the difference between a model stock plan and open to buy? Units versus dollars. The model stock plan states the quantity baseline per SKU; open to buy states how many dollars of purchasing remain this month after subtracting on hand and on order from the planned level. The baseline feeds the OTB calculation — plan minus holdings minus commitments — but neither replaces the other.

How do you calculate model stock? Average daily sales × target cover days, per SKU: a notebook selling 36 a month runs 1.2/day, so a 42-day cover target gives a baseline of about 51 units. Repeat per SKU, sum the values at cost, and the category total is your planned holding. Rerun it when sales expectations or cover targets change, not on a fixed annual schedule.

How many weeks of cover should I plan for? Start from the SKU's role: 6–8 weeks for never-out staples, 4–6 for seasonal core, 2–3 for tests and trends. These are practice starting points, not benchmarks — adjust against your actual supplier lead times and cash position. A SKU whose lead time runs 5 weeks needs a higher baseline than the same seller with a 10-day domestic supplier.

Is a model stock plan the same as a reorder point? No — one is the target, the other is the trigger. The reorder point fires an order when stock falls to demand-during-lead-time plus buffer; the baseline states where you want holding to sit overall. A SKU can trigger a reorder while sitting above baseline, or sit below baseline with no trigger yet. Both columns belong in the same sheet.

Next step

Write the baseline for one category this week — your ten fastest staples at a six-week cover target is enough to start — and park it as a column in your reorder sheet next to on hand. Then book the quarterly session where the range review and the baseline rewrite happen together, so what you carry and how many you hold always come from the same decision.