Forecasting
Forecast Error: How a 30% Miss Sneaks In
Every optimistic pitch is a forecast, and every forecast carries a quiet number called percentage error: |actual − predicted| ÷ actual. It answers how wrong a projection really was — and whether "we hit 130% of plan" is a triumph or a rounding artifact. Run the math on an important number with the percent-change mode.
Where the 30% miss comes from
Say a sales forecast predicted $130,000 and the result was $100,000. Percentage error is:
|100,000 − 130,000| ÷ 100,000 = 30%
The denominator is the actual value, not the prediction. Forecasting errors compound fast because over-promising 30% and then "only" hitting $90,000 is a 44% error — the miss grows the further you undershoot.
Why optimism inflates the error
- Forecasters anchor to an ambitious target instead of a realistic midpoint.
- Errors stack when plans are read backwards — final number, no sensitivity check.
- Everyone wants the "achievable stretch," which quietly becomes the headline claim.
The result: real-world forecasts cluster around a low double-digit miss even when each individual estimate feels reasonable.
The sanity check that catches it
Before trusting any projection, compute the error you'd survive. Ask: if actuals land 30% below plan, is the business still fine? If the answer is no, the forecast was never a forecast — it was hope wearing a spreadsheet. The percent-change calculator turns that "if" into a concrete number in two seconds.
Present the range, not the point
Give a low, base and high scenario and show the percentage spread between them. A forecast that admits its own error is more useful than one that hides it — accuracy is a percentage, and percentages are exactly what this calculator settles.