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What is WAPE and when should I use it instead of MAPE?
WAPE is weighted absolute percentage error: the sum of absolute errors across all items and periods divided by the sum of actual values. It weights errors by volume, so big sellers matter more, and it avoids division by zero for individual items. Use it when you forecast many products with uneven sales.
Compare with MAPE, which treats a 50 percent miss on a tiny item the same as a 50 percent miss on your best seller. WAPE instead answers: of all the volume we sold, what share did we miss by?
It is simple to explain to managers. Still:
- It can hide poor performance on small but important items.
- Report it alongside bias.
- Pick one consistent aggregation level, because WAPE changes with it.
Some teams call this metric the volume-weighted MAPE.
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