Mean Absolute Percent Error (MAPE)
Mean Absolute Percent Error (MAPE) is the most common measure of forecast error. MAPE functions best when there are no extremes to the data (including zeros).
With zeros or near-zeros, MAPE can give a distorted picture of error. The error on a near-zero item can be infinitely high, causing a distortion to the overall error rate when it is averaged in. For forecasts of items that are near or at zero volume, Symmetric Mean Absolute Percent Error (SMAPE) is a better measure.
MAPE is the average absolute percent error for each time period or forecast minus actuals divided by actuals:
Additional forecast error methods include: