Calculators
Symmetric Mean Absolute Percentage Error Calculator
Calculate sMAPE from actual and predicted pairs using the 0–200% convention, entirely in your browser.
Compare forecast errors with a symmetric denominator.
sMAPE = (100 / n) × Σ[2 × |predicted − actual| / (|actual| + |predicted|)]. This calculator uses the 0–200% convention; other definitions can use a 0–100% scale, so compare formulas before comparing results. Both-zero pairs contribute 0% and are included in n. Exactly one zero or opposite signs give 200%. For actual 100 and predicted 90 the result is approximately 10.5263157895%; swapping the values gives the same result. Lower values indicate smaller errors; sMAPE is not an accuracy percentage. Near-zero pairs can still dominate interpretation, and signed values may be difficult to interpret. Use consistent units and the same observations when comparing forecasts. Enter up to 10000 pairs, one per line, with a comma, semicolon, or space separating actual and predicted. Scientific notation is supported; omit thousands separators. Nonzero magnitudes must be between 1e-100 and 1e100. Scaled ratios and compensated summation reduce rounding error. Results show up to 12 significant digits. All data stays in your browser.
Frequently Asked Questions
Everything you need to know about this tool, how it works, and privacy.
How is sMAPE calculated?
Average 200 × |predicted − actual| / (|actual| + |predicted|) across all pairs. Actual 100 and predicted 90 give approximately 10.5263157895%.
How are zeros handled?
A both-zero pair contributes 0% and remains in the average. Exactly one zero contributes 200%. This explicit convention avoids undefined division for both-zero pairs.
Why do some tools report half this value?
Some sMAPE definitions omit the factor of two and use a 0–100% range. This calculator uses 0–200%; compare the formulas before comparing scores.
Is sMAPE an accuracy score?
No. Lower is better, but subtracting sMAPE from 100 does not give a general accuracy score. Near-zero values and signed data can make percentage errors difficult to interpret.
Are my observations uploaded?
No. All calculations run locally in your browser with up to 10000 pairs.