Project a linear trend forward and quantify its fit.
Linear projection is simple but its uncertainty widens the further ahead you go. Bounds that widen with horizon are what distinguish an honest forecast from a point estimate. Extrapolating a linear trend far beyond the observed range is the most common forecasting error, because real series eventually saturate or turn.
Trend Projection
Projection = start + slope × periods; prediction bounds widen with distance from the data
Projection = start + slope × periods; prediction bounds widen with distance from the data Linear projection is simple but its uncertainty widens the further ahead you go. Bounds that widen with horizon are what distinguish an honest forecast from a point estimate.
Extrapolating a linear trend far beyond the observed range is the most common forecasting error, because real series eventually saturate or turn.
This calculator takes 4 inputs: Value at the start of the series, Trend slope per period, Periods ahead to project, Residual standard error. The pre-filled defaults are a realistic starting point — replace them with figures from your own environment for a result you can act on.