Independent Samples t-Test Calculator
Compare the means of two independent groups without installing SPSS or wrestling with syntax: paste your raw data (or just enter n, mean and standard deviation for each group) and get the t statistic, degrees of freedom, exact p-value, mean difference with its 95% confidence interval, and effect sizes (Cohen's d, Hedges' g) instantly. Welch's correction — the recommended default when variances differ — is applied unless you choose the classic pooled (Student) test. Unlike most online calculators, assumption checks run automatically: Shapiro-Wilk tests normality in each group and Levene's test checks equality of variances, with a plain-language warning when something looks off. Verified against R's t.test() to at least six significant digits.
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Frequently asked questions
How do I report independent t-test results in APA 7 format?
Report the t statistic with degrees of freedom, the p-value, and an effect size, e.g.: "Group A scored significantly higher than Group B, t(19.43) = 4.33, p < .001, d = 1.79, 95% CI [1.47, 4.23]." The AI Report button generates a complete APA 7 results paragraph as a Word document from your numbers.
Should I use Welch's t-test or Student's (pooled) t-test?
Welch's t-test is the safer default: it does not assume equal variances and loses almost no power when variances are in fact equal. Use the pooled test only when you have good reason to assume equal variances — this calculator runs Levene's test automatically to help you decide.
Can I run the test with only means and standard deviations?
Yes. Switch to summary input and enter n, mean and SD for each group — exactly what you find in published papers. The results are identical to those computed from raw data.
What does Cohen's d mean here?
Cohen's d expresses the mean difference in pooled standard deviation units. As a rule of thumb: 0.2 is small, 0.5 medium, 0.8 large. Hedges' g is the small-sample-corrected version reported alongside it.