Demand planning
Demand planning is the process of turning a demand forecast into an agreed plan for what to buy, when to buy it and how much cash it will tie up. It takes the forecast number and applies the real constraints: supplier lead times, minimum order quantities, planned promotions, safety stock and the cash available. An ecommerce operator uses it so marketing, operations and finance commit to one plan instead of three.
| Variable | What it covers |
|---|---|
| Forecast demand | Expected units per day from the demand forecast, adjusted for any promotion marketing has planned. |
| Lead time + review period | Days until the order lands, plus days until you next get to reorder. The order has to cover both. |
| Safety stock | A buffer against the forecast being wrong or the supplier being late. |
| Stock on hand and on order | What you already have or have already bought, so it is not bought twice. |
The formula gives the unconstrained answer. Demand planning is the step that checks it against minimum order quantities, cash and the promo calendar, then agrees a final number.
Worked example
Worked example / demonstrative numbers. Without the promo in the plan, the order would have been 800 units, below the supplier minimum, and the promotion would have run into a stockout.
Demand planning vs demand forecasting
The two are often used as synonyms, and they should not be. Demand forecasting is an estimate: how many units customers are likely to want, per SKU, per period. It should be as unbiased as possible, which means it ignores what you would like to happen. Demand planning is a decision process built on that estimate. It adds the things a forecast leaves out on purpose: promotions marketing intends to run, the supplier's minimums and lead times, how much working capital the business can spare, and whether a slow SKU should be bought at all. The forecast answers "what will happen?"; the plan answers "what are we going to do about it?"
What does good demand planning look like?
There is no single accuracy score for a plan, because a plan is judged by outcomes: few stockouts on the SKUs that matter, little stock drifting toward dead stock, and cash tied up in inventory that turns. In practice, good planning has a fixed cadence (often monthly), one shared forecast rather than a marketing number and an ops number, a promo calendar that feeds the forecast before purchase orders go out, and a written record of why each override was made. It also spends effort unevenly: ABC analysis says which SKUs deserve careful planning and which can run on simple rules. For testing the plan before committing to it, see forecasting and testing the plan.
Demand planning vs related terms
| Term | What it is | How it relates to demand planning |
|---|---|---|
| Demand forecasting | The unit estimate per SKU per period. | The main input. Planning adds constraints and decisions on top. |
| Reorder point | The stock level that triggers a new order. | The day-to-day trigger that carries out the plan between reviews. |
| Open-to-buy | The budget left for new inventory in a period. | The cash ceiling the plan has to fit under. |
| Days of cover | How long current stock lasts at forecast demand. | The check that shows where the plan is running thin. |
| Sales forecast | Expected revenue for a period. | The dollar view; demand planning works in units first. |
Common mistakes
- Planning on the forecast alone. A promotion that marketing knows about and operations does not will empty the shelf in week one.
- Letting the plan edit the forecast. If the forecast is nudged up to justify a bigger order, nobody can later tell whether demand or ambition was wrong.
- Ignoring cash. A plan that is right on units can still be wrong on timing if the purchase orders land before the cash from the last batch comes back. Check the cash conversion cycle.
- Rounding every order up to the minimum. Meeting a supplier minimum on a slow SKU can buy months of excess cover. Sometimes the right answer is to skip the SKU or renegotiate.
- Never reviewing overrides. Planners adjust numbers for good reasons. Record why, then check later which adjustments helped.
Demand planning FAQ
Related
Inside Blufire, S11 Planning & Forecasting projects demand and cash as forecast fans and lets you stress a COGS, AOV or discount change in the what-if lab, while S7 Products / Inventory watches days-of-cover so you reorder before the stockout, not after.
Updated September 2026