LinReg(ax+b) on TI-84: Linear Regression Made Simple

Linear regression finds the line of best fit for your data — and LinReg on TI-84 does it in about 30 seconds. This guide walks through the exact buttons, explains what a, b, r, and r² mean, and shows how to graph your regression line.

Step 1: Turn On Diagnostics (So You Get r and r²)

By default, the TI-84 hides the correlation coefficient. Fix that first:

1. Press 2ND → 0 (CATALOG).
2. Scroll down to DiagnosticOn (press D to jump there faster).
3. Press ENTER twice. The screen confirms Done.

You only need to do this once — it stays on.

Step 2: Enter Your Data

1. Press STAT → 1 (Edit).
2. Clear L1 and L2 if needed: highlight each list name, press CLEAR, then ENTER.
3. Enter your x-values in L1 and the matching y-values in L2.

Both lists must have the same number of entries, or you’ll get an ERR: DIM MISMATCH.

Step 3: Run the Regression

1. Press STAT, arrow right to CALC.
2. Select 4: LinReg(ax+b) and press ENTER.
3. Make sure Xlist is L1 and Ylist is L2 (they are by default), then press ENTER on Calculate.

The output shows:

• a = the slope of the regression line.
• b = the y-intercept.
• r² = the coefficient of determination — the fraction of variation in y explained by x.
• r = the correlation coefficient — strength and direction of the linear relationship (thanks to DiagnosticOn).

Step 4: Graph the Regression Line

To see your line drawn over a scatterplot:

1. Turn on a stat plot: 2ND → Y=, select Plot1, turn it On, set Type to scatterplot, Xlist L1, Ylist L2.
2. Re-run the regression, but this time store the equation: after selecting LinReg(ax+b), press VARS → Y-VARS → 1 (Function) → 1 (Y1) before pressing Calculate. You’ll see LinReg(ax+b) L1, L2, Y1.
3. Press ZOOM → 9 (ZoomStat) to fit the window to your data, then GRAPH.

You’ll see your data points with the line of best fit through them.

What the Numbers Mean

• Slope (a): for each 1-unit increase in x, y changes by a units. Always interpret it in context (“for each additional hour studied, predicted score rises by 4.2 points”).
• Intercept (b): the predicted y when x = 0. Often not meaningful in context — say so if it isn’t.
• r: between -1 and 1. Near ±1 means a strong linear relationship; near 0 means weak. The sign tells you the direction.
• r²: as a percent, it’s the proportion of variation in y explained by the linear model. r² = 0.87 means 87% of the variation is explained.

Common Mistakes to Avoid

• DiagnosticOn forgotten: without it, r and r² never appear and students think the calculator is broken. Do Step 1 first.
• Lists of different lengths: double-check L1 and L2 have matching counts — ERR: DIM MISMATCH always means this.
• x and y swapped: the regression of y on x is not the same as x on y. Keep explanatory (x) in L1 and response (y) in L2.
• ZoomStat skipped: after storing to Y1, the default window rarely shows your data. ZOOM → 9 fixes it instantly.

Frequently Asked Questions

How do I do linear regression on TI-84? Enter x-values in L1 and y-values in L2 (STAT → Edit), then press STAT → CALC → 4: LinReg(ax+b) → Calculate.

How do I get r and r² on my TI-84? Press 2ND → 0, find DiagnosticOn, and press ENTER twice — before running the regression. Then r and r² appear in the output.

What’s the difference between LinReg(ax+b) and LinReg(a+bx)? Just notation: ax+b writes slope first, a+bx writes intercept first. AP Statistics uses the ax+b form, so stick with option 4.

Why do I get ERR: DIM MISMATCH? Your L1 and L2 lists have different numbers of entries. Count both lists and fix the mismatch.

Try It With Sample Data

Enter any paired data and run the steps above on our free online TI-84 Plus CE at https://freeti84calculator.com/ — no download needed. More statistics tutorials are waiting in the guides hub at https://freeti84calculator.com/guides/.