Symmetric Mean Absolute Percent Error (SMAPE)
Symmetric Mean Absolute Percent Error (SMAPE) is an alternative to Mean Absolute Percent Error (MAPE) when there are zero or near-zero demand for items. SMAPE self-limits to an error rate of 200%, reducing the influence of these low volume items. Low volume items are problematic because they could otherwise have infinitely high error rates that skew the overall error rate.
SMAPE is the forecast minus actuals divided by the sum of forecasts and actuals as expressed in this formula: