Predictions are inputs, not verdicts. These guides show how forecasting models work, where they hold up, and how to check one against outcomes before you rely on it.
What the public benchmarks show
| Benchmark | What was forecast | Best entry | Simple reference | Source |
|---|---|---|---|---|
| M4 Competition (2018) | 100,000 time series, yearly to hourly | Smyl (hybrid): OWA 0.821, sMAPE 11.37 | Naive2: OWA 1.000, sMAPE 13.56; Comb (average of three exponential smoothing methods): OWA 0.898 | Official M4 scores |
| M5 Accuracy (2020) | 42,840 Walmart unit sales series, 28 days ahead | YJ_STU: WRMSSE 0.520 | Best benchmark (ES_bu, exponential smoothing): 0.671; seasonal naive: 0.847 | Official M5 scores |
| ForecastBench paper (2024) | 200 questions about future events | Superforecaster median: Brier 0.096 | Public median: 0.121; best LLM (Claude 3.5 Sonnet): 0.122 | Karger et al. |
| ForecastBench tournament (updated 11 November 2026) | Rolling questions about future events | Top AI entry: Brier Index 69.5% (95% CI 68.1 to 71.1) | Superforecaster median: 68.2% (66.8 to 69.8); public median: 63.0%; always 50%: 50.0% | ForecastBench leaderboard |
All checked 13 November 2026. Lower is better for OWA, sMAPE, WRMSSE and the Brier score; higher is better for the Brier Index, which ForecastBench scales so that 100% is perfect and 50% is always forecasting 50%. OWA is the M4's overall weighted average of sMAPE and MASE relative to Naive2, so 0.821 means about 18% better than Naive2. More results, by data level and frequency: where forecasts are reliable.
Score a forecast in your browser
The forecast score calculator takes actuals and forecasts, or probabilities and outcomes, and returns MAE, RMSE, MAPE, bias, a naive-forecast comparison, interval coverage with the Winkler score and the Brier score. The formulas and the cases where each metric misleads are listed under the tool.