Demand forecasting

WAPE (Weighted Absolute Percentage Error)

By the Supply Chain Manager team · Updated October 16, 2026

WAPE (weighted absolute percentage error) is total absolute forecast error divided by total actual demand, so high-volume periods and SKUs carry more weight.

Because it divides the sum of errors by the sum of actuals, a single low-volume week cannot blow it up the way it does MAPE. It also works across a group of SKUs: the result reads as 'our forecast was off by X% of what we sold'.

How to calculate WAPE

WAPE = Σ |Actual − Forecast| ÷ Σ Actual × 100

WAPE example

Illustrative numbers: the same actuals of 100, 50 and 10 against forecasts of 90, 60 and 20 give absolute errors of 10, 10 and 10. WAPE = 30 ÷ 160 = 18.75%, compared with a MAPE of 43%.

Why WAPE matters for distributors

WAPE tracks the units you actually got wrong, which maps directly to excess stock or shortages. That makes it a practical headline measure for a purchasing team.

Common WAPE mistakes

Reading a low portfolio WAPE as proof that every SKU is well forecast.
Forgetting that WAPE says nothing about direction; check bias separately.

WAPE in Supply Chain Manager

Supply Chain Manager backtests several forecasting methods per SKU and picks the one with the lowest WAPE, preferring the simpler model when results are close.

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Examples on this page use made-up round numbers to show the calculation. They are not benchmarks or results from real businesses.