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ANCOVA Calculator

Compare groups on an outcome after removing the effect of one or more covariates, such as a pre-test score. Results include adjusted means and the homogeneity-of-regression-slopes test.

Free · No sign-upReplaces SPSS GLMWorks with your data
Updated · By Bibin Xavier

Data 90 × 12

Paste from Excel, or drop a CSV, TSV or Excel file here.
Example data 90 rows, 12 variables. Data stays in this browser tab.
IDtext · 90 levelsGrouptext · 3 levelsGendertext · 2 levelsAgenumericHours_StudynumericAnxietynumericMotivationnumericPre_ScorenumericPost_ScorenumericExam_ScorenumericPassednumeric · codedSatisfactionnumeric · coded
S001ControlMale2311.2294.660626712
S002WorkshopFemale233.9283.554705402
S003OnlineFemale1810.132455576603
S004ControlMale2613.6413.552555903
S005WorkshopFemale229.7273.656636504
S006OnlineFemale207.9323.865826502
S007ControlFemale206.328372836103
S008WorkshopMale228293.164726213

Variables and options

Covariates 1 selected · min 1
Results update automatically when you change an option.

Results

90 rows · example data
Table 1

Homogeneity of regression slopes

InteractionFdfp
Group × Pre_Score1.262, 84.290

Note. Slopes are similar across groups, so the assumption holds.

Table 2

Tests of between-subjects effects

SourceType III SSdfMSFpPartial η²
Group601.832300.918.73< .001.169
Pre_Score7015.8317015.83203.64< .001.703
Error2962.918634.45

Note. R² = .727.

Table 3

Adjusted (estimated marginal) means

GroupnObserved MAdjusted MSE95% CI
Control3061.0361.961.07[59.83, 64.09]
Online3065.5365.001.07[62.87, 67.13]
Workshop3068.7068.301.07[66.17, 70.44]

Note. Evaluated at covariate mean: Pre_Score = 60.18.

Adjusted means with 95% CI

Interpretation

After controlling for Pre_Score, Group had a significant effect on Post_Score (partial η² = .169). Adjusted means ranged from 61.96 to 68.30.

Controlling for Pre_Score, there was a significant effect of Group, F(2, 86) = 8.73, p < .001, η²p = .169.

How to cite this tool

Using these results in a thesis, journal article, report or class assignment? Please cite this free tool so others can find it. It keeps the site free.

APA 7

Xavier, B. (2026). ANCOVA Calculator [Web application]. FreeStatisticalTools.com. https://freestatisticaltools.com/ancova-calculator/

BibTeX 

@software{xavier_ancova_2026,
  author = {Xavier, Bibin},
  title = {ANCOVA Calculator},
  publisher = {FreeStatisticalTools.com},
  year = {2026},
  url = {https://freestatisticaltools.com/ancova-calculator/},
  note = {Web application}
}

Suggested sentence for your methods section: “The analysis was carried out with the free ANCOVA Calculator tool on FreeStatisticalTools.com (Xavier, 2026).”

What is ANCOVA?

Analysis of covariance (ANCOVA) compares group means on an outcome after statistically removing the effect of one or more covariates, most often a baseline or pre-test score. It increases power and adjusts for group differences at the start.

When to use ANCOVA

Use ANCOVA to compare groups while adjusting for a continuous variable that also affects the outcome, most often a baseline or pre-test score.

Assumptions

  • A linear relationship between covariate and outcome.
  • Homogeneity of regression slopes (tested above).
  • Approximately normal residuals and equal variances.

How to use this tool

  1. Enter your data. Paste columns from Excel, Google Sheets or SPSS with variable names in the first row, or upload a CSV or Excel file. The example data shows the expected layout.
  2. Choose the variables. Select the dependent variable, factor (groups) and covariates.
  3. Read the results. Results update automatically. Read the plain-English interpretation, then use Copy table to paste APA-style tables into Word and Copy for the results sentence.

How to report ANCOVA in APA style

Report the group effect with F, df, p and partial η², then the adjusted means.

Frequently asked questions

What are adjusted means?

Adjusted (estimated marginal) means are the group means predicted when every group has the same covariate value, the overall covariate mean.

What is homogeneity of regression slopes?

ANCOVA assumes the covariate relates to the outcome in the same way in every group. A significant group × covariate interaction violates the assumption.

Can I use ANCOVA for pre-test and post-test data?

Yes. Using the pre-test as a covariate and the post-test as the outcome is usually more powerful than analysing change scores.

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