Sales forecasting: what it can and cannot tell you
A good forecasting model doesn't predict the future, but it helps you plan better. How to use it without expecting miracles.
A forecast isn't a prophecy
No model knows what you'll sell next month. What it does is describe the patterns in your past (trend, seasonality, the effect of promotions) and project them forward. If something changes tomorrow that has never happened before, the model won't know.
That's why a useful forecast always comes with a range: not "you'll sell 1,000 units", but "most likely between 900 and 1,100".
What it can tell you
How much stock to order so you neither run out nor overfill the warehouse. How many people you'll need in peak season. Whether this year's growth is real or down to seasonality. Which months will be slow, so you can plan cash flow in time.
What it can't tell you
What isn't in your data: a new competitor, a change in regulation, a crisis. Nor the why: a model detects that sales rise in December, but doesn't know whether it's the holidays or your campaign. Your team supplies that interpretation.
What a model needs to work
Enough history: seeing yearly seasonality takes at least two years of data, and the more the better. Clean, consistent data: if you switched systems halfway and the numbers don't line up, that has to be fixed first. And context: flag promotions, stock-outs or closures so the model doesn't mistake them for normal demand.
How to use it well
Compare the forecast with what actually happened every month: that tells you how far to trust it, and the model improves. Plan with the range, not the central figure: prepare operations for the high scenario and cash for the low one. And revisit the assumptions when something important changes in the business.