Free Demand Forecast Calculator
Predict inventory needs accurately
Enter up to 12 months of historical demand data and instantly forecast next period demand using Simple Moving Average (SMA) or Weighted Moving Average (WMA).
What Is a Demand Forecast Calculator?
A Demand Forecast Calculator uses your historical sales or usage data to estimate how much of a product you will need in a future period. By applying statistical methods like Simple Moving Average (SMA) or Weighted Moving Average (WMA), it smooths out random fluctuations and identifies the underlying demand trend. Accurate demand forecasting helps you plan purchase orders, allocate warehouse space, and avoid the twin costs of stockouts (lost sales) and overstock (tied-up capital and storage costs).
How to Forecast Demand in 3 Steps
Step 1 — Enter Historical Demand
Add your monthly demand (units sold or consumed) for each past period. You can enter 3 to 12 months of data. The more data you add, the more accurate the forecast.
Step 2 — Choose Method & Period
Select Simple Moving Average (SMA) or Weighted Moving Average (WMA), then pick a 3-period or 6-period window. WMA gives more weight to recent data, making it better when demand is shifting.
Step 3 — Read the Forecast
The calculator shows your predicted demand for the next period, the trend direction based on the last 3 months, and Mean Absolute Error (MAE) so you can judge forecast accuracy.
Who Uses This Demand Forecast Calculator?
Inventory Managers
Predict next month's stock requirements based on historical consumption to plan purchase orders in advance.
Retail Business Owners
Forecast seasonal demand so you stock enough inventory before peak periods without over-buying slow-moving items.
E-commerce Sellers
Avoid stockouts and excess stock by forecasting demand for each SKU using real sales history.
Supply Chain Teams
Build data-driven procurement schedules by comparing SMA and WMA forecasts for different product categories.
Frequently Asked Questions
What is a demand forecast calculator?
A demand forecast calculator uses past sales or usage data to estimate how much of a product you will need in a future period. This helps you plan inventory purchases to avoid stockouts or overstock.
What is Simple Moving Average (SMA)?
SMA averages the demand over the last N periods equally. For a 3-period SMA: Forecast = (Month1 + Month2 + Month3) / 3. It works best when demand is relatively stable.
What is Weighted Moving Average (WMA)?
WMA assigns higher weights to more recent periods. For a 3-period WMA the weights are 0.5 (most recent), 0.3, and 0.2. This makes WMA more responsive to recent demand changes than SMA.
What is Mean Absolute Error (MAE)?
MAE measures how far off your forecasts were from actual demand on average, in units. A lower MAE means a more accurate forecast. It is shown when you have more data than the period length.
How many months of data do I need?
You need at least as many months as your chosen period (3 or 6). More historical data gives better accuracy and also lets the tool calculate MAE to measure forecast quality.
Is this demand forecast calculator free?
Yes, completely free. No login or account required.