Forecast Accuracy Calculator

About this calculator

Forecast accuracy compares what actually happened to what was predicted, most commonly expressed as the percentage error, (Actual − Forecast) / Actual × 100, or averaged across many periods and SKUs as the Mean Absolute Percentage Error (MAPE). A low error means the forecasting model or planner is reliably close to reality; a persistently high or biased error signals a demand-planning process that needs recalibration.

Demand planners, supply chain analysts and retail/FMCG merchandisers track this figure to size inventory and production runs correctly — overforecasting ties up cash in unsold stock, while underforecasting causes stockouts — and it's a standard KPI reported up to S&OP (sales and operations planning) leadership.