Demand Forecast Calculator
Next period's demand from trend and seasonality.
1.0 is average. 1.8 means 80% above the annual average.
Next period forecast
648
540 before the seasonal index
The deviation figure is the useful part — its standard deviation is the correct input to safety stock. A forecast whose error you have measured beats a more accurate one you have not.
How the Demand Forecast Calculator works
A forecast is a structured guess, and its value lies in being consistently structured rather than occasionally right. A moving average with a trend adjustment and a seasonal index beats intuition reliably, and — more usefully — its error can be measured and improved.
Not financial advice. Marketplace fees change, and they vary by country, plan and seller status. Every rate here is an editable default, not a quoted price — check the platform's current fee schedule before you price a product against it. This is not tax or business advice.
Frequently asked questions
What forecasting method should a small business use?
A moving average of recent periods, adjusted for trend and multiplied by a seasonal index. It is simple enough to maintain in a spreadsheet and captures most of the predictable variation. Sophisticated models rarely justify their overhead below significant scale.
How do I build a seasonal index?
Divide each period's actual demand by the average for the year, over two or three years. A December index of 1.8 means December runs 80% above average. Apply the index to the base forecast for the corresponding period.
How accurate should a forecast be?
Mean absolute percentage error of 10-20% is respectable for retail at product level, better in aggregate. Chasing single-digit accuracy at SKU level is usually wasted effort — safety stock exists precisely to absorb what the forecast cannot see.
What should I do about forecast error?
Measure it and use it. The standard deviation of forecast error is the correct input to safety stock. A forecast whose error you have quantified is far more useful than a more accurate one you have not.