How to Do Linear Regression on TI-84 — Complete Step-by-Step Guide (2026)
Linear regression on a TI-84 involves four main steps: enter your x-values in L1 and y-values in L2, run LinReg(ax+b) from the STAT CALC menu, read the slope (a), intercept (b), and correlation coefficient (r) from the output, and optionally graph the regression line over your scatter plot. The whole process takes under two minutes once you know the path. This guide walks through each step with a worked example, explains what every output value means, and covers the common mistakes that cause wrong answers or missing r values.
Enter x-values in L1 and y-values in L2 via STAT → Edit. Then press STAT → CALC → 4: LinReg(ax+b) → set Xlist: L1, Ylist: L2, Store RegEQ: Y₁ → Calculate. Read a (slope), b (y-intercept), r (correlation), and r² (coefficient of determination). Press GRAPH to see the line on your scatter plot.
- The regression equation is ŷ = ax + b where a is the slope and b is the y-intercept.
- r measures strength and direction of the linear relationship (−1 to +1).
- r² tells you what percentage of variation in y is explained by x.
- If r and r² are not showing, you need to enable DiagnosticOn first.
- Store the equation in Y₁ to graph the regression line with one button press.
- Always check your list data before running regression — leftover values from a previous session will corrupt results.
- No TI-84 handy? The free online TI-84 simulator supports full regression workflows.
Before You Start — Enable DiagnosticOn
By default, the TI-84 hides the correlation coefficient (r) and coefficient of determination (r²) from the regression output. You need to turn on DiagnosticOn once — it stays enabled even after the calculator is turned off.
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Press 2nd → 0 (CATALOG) The full function catalog opens in alphabetical order.
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Press D to jump to the D section On TI-84 Plus CE, press the ALPHA key first, then D (the x⁻¹ key). Scroll down until you see DiagnosticOn.
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Press ENTER twice First ENTER pastes
DiagnosticOnto the home screen. Second ENTER executes it. The screen shows Done.
Step 1 — Enter Data into L1 and L2
Regression requires two matched lists: L1 for x-values (the independent variable) and L2 for y-values (the dependent variable). Every x-value must have a corresponding y-value at the same row position.
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Press STAT → 1: Edit The list editor opens showing L1, L2, and L3 columns.
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Clear any existing data first Highlight the L1 header (not a cell below it), press CLEAR → ENTER. Repeat for L2. This prevents old data from mixing with your new input.
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Enter your x-values in L1, pressing ENTER after each Example: 1, 2, 3, 4, 5 — one per row, cursor moves down automatically.
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Move to L2 using the right arrow key and enter your y-values Example: 3.2, 5.1, 6.8, 9.0, 11.3 — matching each x in the same row.
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Press 2nd → MODE (QUIT) to exit the list editor Returns to the home screen. Data is saved automatically.
Step 2 — Create a Scatter Plot (Optional but Useful)
Viewing a scatter plot before running regression lets you visually confirm the data looks linear — not curved or U-shaped — which makes the linear model appropriate. It also lets you spot any obvious outliers before they influence the equation.
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Press 2nd → Y= (STAT PLOT) The STAT PLOT menu opens with three plot options (Plot1, Plot2, Plot3).
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Press 1: Plot1 and set it to On Select the first icon (scatter plot). Set Xlist to L1 and Ylist to L2. Choose a Mark style.
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Press ZOOM → 9: ZoomStat The calculator automatically scales the window to fit your data and plots all points. This is the fastest way to see a properly sized scatter plot.
Step 3 — Run LinReg(ax+b)
With data in your lists, you're ready to run the linear regression calculation. The function is LinReg(ax+b) — option 4 in the STAT CALC menu.
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Press STAT → right arrow to CALC tab The statistical calculation menu opens.
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Press 4: LinReg(ax+b) On newer TI-84 Plus CE firmware, a dialog box appears. On older firmware, the function pastes to the home screen.
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Set Xlist = L1 and Ylist = L2 In the dialog: navigate to Xlist and press 2nd 1 for L1; navigate to Ylist and press 2nd 2 for L2. On the home screen, type:
LinReg(ax+b) L1, L2 -
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Store the equation in Y₁ (strongly recommended) In the dialog, navigate to Store RegEQ and press VARS → 1: Function → 1: Y₁. On the home screen, type the full command:
LinReg(ax+b) L1, L2, Y₁. This lets you graph the line with one press of GRAPH afterward. -
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Press ENTER (or select Calculate in the dialog) The regression output appears instantly.
Step 4 — Reading and Interpreting the Output
The LinReg output screen shows four values. Here's what each one means and how to use it:
a = 2.01 ← slope
b = 1.18 ← y-intercept
r² = 0.9971 ← coefficient of determination
r = 0.9985 ← correlation coefficient
| Symbol | Name | What It Tells You |
|---|---|---|
| a | Slope | For each 1-unit increase in x, y increases by a units. Negative a = inverse relationship. |
| b | Y-intercept | Predicted value of y when x = 0. May not have real-world meaning depending on context. |
| r² | Coefficient of Determination | Proportion of variation in y explained by x. r² = 0.997 means 99.7% of y's variation is explained by the linear model — an excellent fit. |
| r | Correlation Coefficient | Strength and direction of the linear relationship. Ranges from −1 to +1. Values near ±1 indicate strong linearity; near 0 indicates weak or no linear relationship. |
How to Write the Regression Equation
Using the sample output above, the regression equation is:
To predict y for a specific x-value, substitute the x into the equation. For x = 6: ŷ = 2.01(6) + 1.18 = 13.24. You can also use the TRACE function on the graph to read predicted values directly — covered in the next section.
Step 5 — Graphing the Regression Line
If you stored the equation in Y₁ during step 3, graphing the line alongside your scatter plot takes two button presses.
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Confirm STAT PLOT 1 is still On with L1/L2 selected Press 2nd → Y= → Plot1 and verify it's enabled. The scatter plot dots will show alongside the regression line.
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Confirm Y₁ contains the regression equation Press Y= and check that Y₁ shows the equation (not blank). If it's blank, re-run LinReg with Store RegEQ: Y₁.
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Press ZOOM → 9: ZoomStat The window auto-scales to your data and draws both the scatter plot and the regression line together.
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Press TRACE and use arrow keys to read predicted values While on the Y₁ line (press ↑ or ↓ to switch between the scatter dots and the line), type any x-value and press ENTER — the corresponding predicted ŷ appears at the bottom of the screen.
Full Worked Example with Real Data
Let's apply every step to a concrete problem.
Scenario: A student records hours studied and exam scores for 6 classmates.
| Hours Studied (x) | Exam Score (y) |
|---|---|
| 1 | 52 |
| 2 | 58 |
| 3 | 65 |
| 4 | 71 |
| 5 | 78 |
| 6 | 85 |
Entering Data
- Press STAT → Edit → clear L1 and L2
- Enter 1, 2, 3, 4, 5, 6 in L1
- Enter 52, 58, 65, 71, 78, 85 in L2
- Quit to home screen
Running LinReg
- Press STAT → CALC → 4: LinReg(ax+b)
- Set Xlist: L1, Ylist: L2, Store RegEQ: Y₁
- Press ENTER / Calculate
Results
a = 6.6286 ← score increases ~6.6 pts per hour
b = 45.667 ← predicted score at 0 hours
r² = 0.9983 ← 99.8% of score variation explained
r = 0.9991 ← very strong positive correlation
Regression equation: ŷ = 6.63x + 45.67
Interpretation: Each additional hour of study predicts about 6.6 more points on the exam. The correlation of 0.999 indicates an almost perfectly linear relationship in this data set.
Prediction: For a student who studies 7 hours: ŷ = 6.63(7) + 45.67 = 92.1
Other Regression Types Available on TI-84
Linear regression is the most common, but the TI-84's STAT CALC menu includes several other regression models. Use these when a scatter plot suggests a non-linear pattern.
All regression types follow the same workflow: enter data in lists, select the appropriate function from STAT → CALC, specify L1 and L2, optionally store in Y₁, and press Calculate. The output format varies slightly but always includes the equation coefficients.
Common Mistakes and How to Fix Them
| Problem | Cause | Fix |
|---|---|---|
| r and r² not showing in output | DiagnosticOn not enabled | Press 2nd → CATALOG → scroll to DiagnosticOn → ENTER → ENTER. Now re-run LinReg. |
| ERR: DIM MISMATCH | L1 and L2 have different numbers of entries | Go to STAT → Edit and count rows. Delete extra values or add missing ones so both lists match. |
| Wrong regression equation — impossible slope | Old data still in L1 or L2 from previous session | Clear lists before entering new data: highlight the list header in STAT Edit → CLEAR → ENTER. Or see the reset guide for ClrAllLists. |
| Regression line not appearing on graph | Equation was not stored in Y₁, or Y₁ is disabled | Re-run LinReg and include Y₁ as the Store RegEQ destination. Check that Y₁'s = sign is highlighted in the Y= menu. |
| Scatter plot not visible with regression line | STAT PLOT is turned off | Press 2nd → Y= → Plot1 → On. Then press ZOOM → ZoomStat to redraw. |
| r is negative when relationship looks positive | X and Y lists entered in wrong order (swapped) | Check that your x-values are in L1 and y-values are in L2 — not the other way around. The sign of r matches the sign of the slope a. |
| TRACE not showing ŷ values on the regression line | Cursor is on the scatter plot dots, not the Y₁ line | While in TRACE mode, press ↑ or ↓ to switch between the scatter plot and the stored regression equation. The top-left shows which function is active. |
Practice Linear Regression Right Now — Free
Open the free TI-84 online simulator, enter your data in L1 and L2, and run LinReg — no physical calculator needed.
Open Free TI-84 Simulator →Related TI-84 Statistics Guides
Linear regression sits at the intersection of several statistics skills. These guides cover the techniques that connect directly to it:
Frequently Asked Questions
How do I do linear regression on a TI-84 calculator?
Enter x-values in L1 and y-values in L2 via STAT → Edit. Then press STAT → CALC → 4: LinReg(ax+b). Set Xlist to L1 and Ylist to L2 — optionally store the equation in Y₁. Press Calculate. The output shows a (slope), b (y-intercept), r², and r.
Why is r not showing in my TI-84 regression output?
The TI-84 hides r and r² by default. You need to enable DiagnosticOn: press 2nd → 0 (CATALOG) → scroll to DiagnosticOn → press ENTER twice. The screen confirms with "Done." Now re-run your LinReg and r will appear. This setting persists until an All Memory reset.
What is the difference between a and b in TI-84 LinReg output?
In the equation ŷ = ax + b, a is the slope — it tells you how much y changes for each 1-unit increase in x. b is the y-intercept — the predicted value of y when x equals zero. For example, if a = 3.5 and b = 2.0, the equation is ŷ = 3.5x + 2.0, meaning each additional unit of x adds 3.5 to the predicted y.
How do I graph the regression line on TI-84?
When running LinReg, store the equation in Y₁ by selecting it in the Store RegEQ field (or append Y₁ to the command on the home screen). Then make sure STAT PLOT 1 is enabled with L1/L2 selected. Press ZOOM → 9: ZoomStat — the scatter plot and regression line both appear. Use TRACE and arrow keys to read predicted values along the line.
What does r² mean in linear regression on TI-84?
r² (the coefficient of determination) tells you what proportion of the variation in your y-values is explained by the linear relationship with x. An r² of 0.95 means 95% of the variation in y is accounted for by the model — only 5% is unexplained. Values closer to 1 indicate a better-fitting linear model. An r² below 0.5 generally suggests a weak linear fit.
What is ERR: DIM MISMATCH in TI-84 regression?
This error appears when L1 and L2 have different numbers of entries. Every x-value in L1 needs a matching y-value in L2 at the same row position. To fix it: go to STAT → Edit and count the rows in each list. Add the missing value or remove the extra one. If old data is causing confusion, clear both lists completely by highlighting each list header and pressing CLEAR → ENTER.
Can I do linear regression on the TI-84 online simulator?
Yes. The free TI-84 simulator at ti84calculato.com supports the full STAT menu including LinReg(ax+b), list editing, and scatter plots via STAT PLOT. Every step in this guide works identically on the online version — useful for practice or for verifying results when you don't have a physical calculator available.
How do I predict a y-value from my regression equation on TI-84?
There are two methods. First, substitute the x-value directly into the equation on the home screen: type a × x + b using your actual values from the LinReg output. Second (easier): after storing the equation in Y₁ and graphing, press TRACE, make sure the cursor is on the Y₁ line, type your x-value, and press ENTER. The calculator jumps to that point and displays the predicted ŷ at the bottom of the screen.
Linear Regression in Five Steps
The complete regression workflow on a TI-84 follows a consistent path: enable DiagnosticOn once, enter paired data in L1 and L2, run LinReg(ax+b) from STAT → CALC, read the slope and intercept from the output, and graph the line by storing the equation in Y₁. The r and r² values tell you immediately how well the linear model fits — values above 0.95 generally indicate a strong relationship worth using for predictions.
Regression connects naturally to other statistics skills on the TI-84. The same list workflow you use here applies to 1-Var Stats for standard deviation, and the correlation coefficient r links directly to Z-scores and normal distribution calculations. For the full collection of TI-84 tutorials covering every exam-relevant function, visit the Guides & Tutorials section.