A forecast is only as steady as the top of your funnel
The short answer
Forecast by applying stage-to-stage conversion rates to what is currently in the pipeline. It only works with clean data and a steady flow of new opportunities. An irregular top of funnel makes any forecast fiction.
Forecasts are usually wrong for one of two boring reasons: the data is dirty, or the pipeline arrives in bursts.

The basic method
Take how many opportunities sit at each stage, apply the rate at which each stage historically converts to the next, and you have an expectation. That is the whole mechanism; the difficulty is entirely in the inputs.
What has to be true first
Three conditions, and forecasts fail when any is missing:
- Stages mean something, and everyone applies them the same way.
- Records are current, so the pipeline reflects reality.
- Enough volume, that conversion rates are not noise.
Why forecasts swing
The usual culprit is a pipeline filled in bursts. A month of heavy prospecting followed by a month of none produces a forecast that lurches, and no amount of spreadsheet sophistication fixes it.
A steady flow of new conversations is what makes a forecast stable, which is the least exciting and most important part of the answer.
Stale deals distort everything
A deal sitting untouched in a late stage inflates the forecast while being, in practice, already lost. Regular cleanup is not tidiness, it is what stops the number from lying. This is where CRM hygiene pays for itself.
What a bad forecast tells you
If the number is consistently wrong in one direction, that is information. Consistently high usually means dead deals are not being closed out. Consistently low usually means stage criteria are too strict. Either way it points at the process rather than the spreadsheet.
Frequently asked
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