Free Linear Regression Calculator — Equation, R

What Is a Regression Calculator?

A regression calculator is a statistical tool that finds the best-fit line through a set of paired data points using the least squares method. It computes the slope and intercept of the regression line, the R² (coefficient of determination), the correlation coefficient (r), and a full predictions table with residuals — all from your raw x and y values.

Whether you're analyzing sales trends, scientific measurements, or academic data, linear regression is one of the most widely used statistical techniques. This calculator handles every step of the process — from the summation formulas to the final equation — so you can focus on interpreting your results rather than crunching numbers.

Common Use Cases

• Line of best fit - Find the equation y = mx + b that minimizes the total squared error across all your data points
• R-squared (R²) - Measure how much of the variation in y is explained by x, expressed as a value between 0 and 1
• Correlation coefficient (r) - Determine the strength and direction of the linear relationship between your variables
• Predictions table - See the predicted y-value for every x in your dataset, laid out in an easy-to-read table
• Residuals analysis - Review the difference between each observed and predicted value to assess model fit
• Formula breakdown - Follow every summation and substitution so you understand exactly how the results were derived

Why Regression Is Challenging by Hand

• Multiple summations required - You need Σx, Σy, Σxy, Σx², and Σy² before you can even start computing slope or intercept
• Complex slope formula - The least squares slope involves a fraction with products of sums in both numerator and denominator, making arithmetic errors extremely common
• R² adds more work - After finding the regression line, computing the coefficient of determination requires additional summations and squared terms
• Residuals for every point - Checking model fit means calculating ŷ and the residual (y − ŷ) for each data point individually, which is tedious for large datasets

How It Works

Enter your paired data as x-values and y-values. The calculator computes all the intermediate summations, applies the least squares formulas to find the slope (m) and intercept (b), and returns the full regression equation. It then calculates R², the correlation coefficient r, and builds a predictions table showing observed values, predicted values, and residuals for every data point.

The step-by-step breakdown shows each summation, the substitution into the slope and intercept formulas, and the derivation of R² — so you can follow along or verify against your own work.

Example

Given x: 1, 2, 3, 4, 5 and y: 2.1, 3.9, 6.2, 7.8, 10.1, the calculator computes Σx = 15, Σy = 30.1, Σxy = 112.3, Σx² = 55, then derives the slope m = 1.98 and intercept b = 0.04. The result is y = 1.98x + 0.04 with an R² = 0.998, indicating an extremely strong linear fit.

Key Examples

• Science lab data - Plot temperature vs. reaction rate and find the regression equation to predict rates at new temperatures
• Sales forecasting - Fit a line to monthly revenue figures and project future months
• Academic grading - Correlate study hours with exam scores to quantify the relationship
• Engineering calibration - Use regression to calibrate sensor readings against known reference values
• Economic analysis - Model the relationship between advertising spend and conversion rates

Benefits of Using This Calculator

• Instant results - Paste your data and get the regression equation, R², correlation, and residuals in seconds
• Step-by-step formulas - Every summation and substitution is shown so you can learn or verify the math
• Full predictions table - See observed vs. predicted values and residuals for every data point at a glance
• No software needed - Skip spreadsheets and statistical packages for straightforward linear regression tasks
• Free and private - Your data is processed in your browser and never stored on our servers

Frequently Asked Questions

What type of regression does this calculator perform?

This calculator performs simple linear regression (ordinary least squares), which fits a straight line y = mx + b to your data. It's designed for two-variable datasets where you want to model a linear relationship between x and y.

How do I enter my data?

Type or paste your x-values and y-values as comma-separated lists. The calculator matches them by position — the first x pairs with the first y, and so on. Both lists must have the same number of values.

What does R² actually tell me?

R² (the coefficient of determination) tells you what fraction of the variation in y is explained by the linear model. An R² of 0.95 means 95% of the variability in your y-values can be accounted for by the regression line. Higher values indicate a better fit.

What is the correlation coefficient?

The correlation coefficient r measures the strength and direction of the linear relationship. It ranges from −1 (perfect negative correlation) to +1 (perfect positive correlation). An r near 0 means little to no linear association.

What are residuals and why do they matter?

A residual is the difference between an observed y-value and the predicted y-value from the regression line. Examining residuals helps you spot outliers, check whether a linear model is appropriate, and assess overall model accuracy.

Is my data kept private?

Yes. All calculations run directly in your browser. Your data is never uploaded to or stored on any server, so you can work with sensitive or proprietary datasets with confidence.

More Calculators