Paired T-Test Calculator
Before-and-after comparison with t, df, p-value and effect size.
Enter your values
ⓘ Live results
Results
- t statistic
- 7
- p-value (two-tailed)
- 0.0009
- Verdict
- p < 0.001 — very strong evidence
- Mean difference
- 2.3333
- SD of differences
- 0.8165
- Degrees of freedom
- 5
- Cohen's d
- 2.858
Quick answer
A paired t-test analyses the differences within each pair: t = mean difference ÷ (SD of differences ÷ √n), with n − 1 degrees of freedom.
t = d̄ ÷ (s_d ÷ √n)
How to use the Paired T-Test Calculator
- 1Enter the before measurements in order.
- 2Enter the after measurements for the same subjects in the same order.
- 3Read t and the p-value, then check Cohen's d for how big the change actually is.
Worked example
Using the values the calculator loads with:
Inputs
- Before values12, 15, 11, 14, 13, 16
- After values14, 18, 12, 17, 15, 19
Results
- t statistic7
- p-value (two-tailed)0.0009
- Verdictp < 0.001 — very strong evidence
- Mean difference2.3333
- SD of differences0.8165
- Degrees of freedom5
- Cohen's d2.858
Frequently asked questions
When do I use a paired test instead of an independent one?
When each pair of numbers comes from the same person, item or matched unit — pairing removes between-subject variation and gives far more power.
What if my lists are different lengths?
The test cannot run: every observation needs a partner. Use an independent two-sample t-test instead.
About this calculator
- Built and reviewed by James Whitfield · How we build and test calculators
- Report an error
Results are estimates for general information. For medical, legal, structural or financial decisions, confirm with a qualified professional.