What Is Demand Planning?
Demand planning uses data to forecast future customer demand. The foundation of effective inventory and supply chain management.
Key Takeaways
- Demand planning predicts future customer demand to drive procurement and production decisions
- Statistical forecasting combines historical sales with seasonal, trend, and event adjustments
- Forecast accuracy is measured by MAPE (Mean Absolute Percentage Error)
- Collaboration between sales, marketing, and operations improves forecast accuracy
What demand planning is
Demand planning is the process of forecasting how much of each product customers will buy in a future period, and using that forecast to drive procurement, production, and inventory decisions. Without demand planning, businesses carry too much inventory (tying up cash) or too little (causing stockouts and lost sales).
Inputs to a demand plan
A demand plan draws on: historical sales data by SKU, seasonal patterns, trend analysis (is the product growing or declining?), forward-looking events (upcoming promotions, new product launches, competitor activity), and external signals (market growth data, economic indicators). Statistical models combine these inputs to generate a baseline forecast.
Statistical methods
The most common methods are moving averages (simple but useful for stable demand), exponential smoothing (weights recent data more heavily — useful when trends are changing), and seasonal decomposition (separates trend from seasonal effects). More advanced methods include ARIMA and machine learning models. The right method depends on data volume and demand pattern complexity.
Forecast accuracy
Demand forecast accuracy is typically measured by MAPE — Mean Absolute Percentage Error. A MAPE below 20% for A items is achievable and represents good forecasting practice. The goal is not perfection — demand is inherently uncertain — but consistent reduction in forecast error through better data, better methods, and better collaboration.
S&OP: the collaborative process
Demand planning works best when it is not done in isolation. Sales and Operations Planning (S&OP) is a monthly cross-functional process aligning the demand plan with supply capacity and financial targets. Sales and marketing bring market intelligence. Operations brings supply constraints. Finance brings financial targets. The output is a single agreed plan all functions commit to executing.