Latest APE
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S&P 500 Forecast Error
This chart tracks the absolute percent error of the prior S&P 500 forecast and its rolling mean absolute percent error.
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12-month MAPE
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Latest 12 observations
5-year MAPE
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Latest 60 observations
Full-history MAPE
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Understanding APE and MAPE
Both measures describe the size of a forecast miss as a percentage of the actual S&P 500 value. Because the error is absolute, it is positive whether the forecast was too high or too low.
APE: one month’s forecast error
Absolute Percent Error measures how far the prior forecast was from the actual value for a single month.
APE = |Actual − Forecast| ÷ Actual × 100An APE of 2% means the forecast missed the actual value by 2%, regardless of direction.
MAPE: average error over time
Mean Absolute Percent Error is the average of the individual APE readings across a selected period.
MAPE = (APE₁ + APE₂ + … + APEₙ) ÷ nThe chart’s line uses a rolling 12-month MAPE, which smooths month-to-month swings in forecast accuracy.
How to read the chart: lower APE and MAPE values indicate more accurate forecasts; 0% represents a perfect forecast.
Absolute Percent Error and MAPE
Monthly absolute percent error with a rolling 12-month mean.
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Monthly S&P 500 absolute percent errors with a rolling 12-month mean absolute percent error line.
Monthly APE
12-month MAPE
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What the history shows
Monthly bars show APE; the line shows the rolling 12-month MAPE. Source: Financial Forecast Center's internal tracking data.
Recent monthly readings
| Month | APE | 12-month MAPE |
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