Paired T-Test Calculator
Before-and-after comparison with t, df, p-value and effect size.
Enter your values
Enter the before values you are working with.
Enter the after values you are working with.
Results update instantly as you type — no submit needed. Your values are remembered on this device, and the shareable link reopens the calculator with exactly these numbers.
- 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)
At a glance
| What it does | Before-and-after comparison with t, df, p-value and effect size. |
|---|---|
| Category | Statistics |
| Inputs needed | Before values, After values |
| Main output | t statistic |
| Formula | t = d̄ ÷ (s_d ÷ √n) |
| Cost | Free — no sign-up, no download |
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.
Inputs explained
- Before values
- Enter the before values you are working with.
- After values
- Enter the after values you are working with.
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.
What do I need to enter into the Paired T-Test Calculator?
Just 2 values: before values, after values. Every field starts with a realistic example, so you can change one number at a time and watch the result update instantly.
How does the Paired T-Test Calculator work out the answer?
A paired t-test analyses the differences within each pair: t = mean difference ÷ (SD of differences ÷ √n), with n − 1 degrees of freedom. It applies the formula t = d̄ ÷ (s_d ÷ √n) and shows the working so you can check each step by hand.
Is the Paired T-Test Calculator free, and do I need an account?
It is completely free with no sign-up, no download and no usage limit. Everything is calculated in your browser, so the numbers you type never leave your device.
Results are estimates for general information. For medical, legal, structural or financial decisions, confirm with a qualified professional.