What this calculator does
A residual measures how far a model’s prediction is from the actual observed value. Residuals are a core building block of regression analysis, used to judge how well a model fits the data.
How the calculation works
The residual is simply the observed value minus the predicted value: residual = observed – predicted. A positive residual means the actual value was higher than predicted (the model underestimated), while a negative residual means the actual value was lower than predicted (the model overestimated). The calculator also reports the squared residual, which is used in methods like least-squares regression, and the percent error relative to the observed value.
A good-fitting model tends to have residuals close to zero and randomly scattered, without an obvious pattern. This tool is for general statistics and educational use.