Demand Planning vs Inventory Planning: What's the Difference?

These two terms get used interchangeably. They shouldn't be — because confusing them leads brands to solve the wrong problem.

The short version: demand planning is about forecasting what you'll sell. Inventory planning is about deciding what to stock. One is an input. The other is the decision that input drives.

Here's how they're distinct, how they connect, and why most small brands are doing one without the other.

Demand Planning

Demand planning is the process of forecasting future customer demand — in units, by SKU, by channel, over time.

It answers the question: how much of this product are we going to sell, and when?

The output of demand planning is a forward-looking unit forecast. That forecast is built from historical sales data, adjusted for seasonality, promotions, new product launches, and any changes in the business. It gets updated monthly as actuals come in and assumptions evolve.

Good demand planning doesn't require perfect data or expensive software. It requires a consistent method, honest inputs, and a regular process for comparing the forecast to what actually happened.

A demand plan is wrong by definition — no forecast is perfectly accurate. The goal is to be wrong in a small, manageable way rather than a large, expensive one.

Inventory Planning

Inventory planning is the process of deciding how much stock to hold and when to reorder — given what your demand plan says you'll sell and the realities of your supply chain.

It answers the question: how much should we have on hand, and when do we need to order more?

The output of inventory planning is an ordering schedule: specific reorder dates and quantities for each SKU, calculated from your demand forecast, your lead times, your safety stock targets, and your supplier's minimum order quantities.

Inventory planning without a demand plan is guesswork. You're deciding how much to stock without knowing how much you'll sell. Most brands at $5M–$15M are in this position — they're managing their stock levels reactively (order more when it gets low, order less when the warehouse is full) without a forward-looking demand signal telling them what "low" and "full" actually mean given what's coming.

How They Work Together

Demand planning feeds inventory planning. In sequence:

Demand plan: You forecast 800 units of your hero SKU next month, based on historical velocity and a planned promotional event
Inventory plan: Given that forecast, your current on-hand inventory, your lead time of 6 weeks, and your safety stock target of 200 units, your inventory plan tells you to place a purchase order for 600 units today

Remove step one and step two becomes a guess. The reorder quantity isn't derived from anything — it's based on instinct, habit, or whatever the co-man's MOQ happens to be.

This is why brands that "just do inventory planning" — tracking stock levels and placing orders when things get low — consistently end up either overstocked or understocked. They're managing the present without modeling the future.

The Third Piece: Demand Forecasting

You'll also hear the term demand forecasting, which is sometimes used interchangeably with demand planning but refers specifically to the statistical or analytical process of generating the forecast itself.

If demand planning is the broader discipline — the process, the cadence, the cross-functional conversation — then demand forecasting is the technical engine inside it. The weighted moving average, the seasonality index, the regression model. Forecasting is what produces the number. Planning is what you do with it.

All three terms are related:

Which One Do Most Small Brands Actually Have?

Usually neither — at least not in a formal sense.

What most founder-led brands have is a purchasing habit: they order when stock gets low, they order more when they're nervous about a promotion, and they order less when the warehouse is full. That's not a plan. It's a reaction.

The most common gap we see is brands that have some version of inventory tracking (they know what's on hand) but no forward-looking demand model. They know where they are. They don't know where they're going.

That gap is where stockouts and overstock live. You can't know whether your current inventory is too high or too low without a view of what demand is coming. And you can't build that view without a demand plan.