If you expect the data trend to continue uniformly, then extrapolation is usually acceptable. The problem rises when the data no longer fits the model you use to make your predictions. An example is the data for HIV and AIDS.

Should extrapolation ever be used?

Extrapolation is using the regression line to make predictions beyond the range of x-values in the data. Extrapolation is always appropriate to use. ... Extrapolation is using the regression line to make predictions beyond the range of x-values in the data. Extrapolation should not be used.

Is it okay to extrapolate?

In general, it is dangerous to extrapolate beyond the scope of model. The following example illustrates why this is not a good thing to do. The moral of the story is that the trend in the data as summarized by the estimated regression equation does not necessarily hold outside the scope of the model.