What this calculator does
The coefficient of determination, R-squared (R²), shows how much of the variation in your actual values is explained by a model’s predictions. It is commonly used to judge how well a regression line or forecasting model fits real data.
How the calculation works
The calculator computes the sum of squared residuals (the squared differences between actual and predicted values) and the total sum of squares (the squared differences between actual values and their own mean). R² = 1 – (sum of squared residuals / total sum of squares). An R² of 1 means the model predicts the actual values perfectly, while an R² of 0 means it explains none of the variation beyond simply guessing the average.
Enter at least 2 complete actual/predicted pairs. This tool is for general and educational statistical use.