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Confidence Interval Calculator
Confidence interval for a mean (t or z).
49.7095 … 54.8905
Interval
± 2.5905
Margin of error
1.2807
Standard error
2.0227
t (df = 39)
Runs entirely in your browser. Nothing is sent anywhere.
How it works
- 1Enter your values.
- 2See the result update instantly as you type.
- 3Change any value to compare scenarios.
About this tool
Confidence Interval Calculator: Confidence interval for a mean (t or z). Type your numbers and the result is calculated instantly — no button to press, nothing to install. All math runs locally in your browser, so the values you enter are never sent anywhere.
Example
| Input | |
|---|---|
| Mean | 52.3 |
| Standard deviation | 8.1 |
| Sample size n | 40 |
| Confidence level | 95 % |
| Population standard deviation is known (z) | No |
| Result | |
| Interval | 49.7095 … 54.8905 |
| Margin of error | ± 2.5905 |
| Standard error | 1.2807 |
| t (df = 39) | 2.0227 |
How do I use the Confidence Interval Calculator?
Enter your values. See the result update instantly as you type. Change any value to compare scenarios.
Is the Confidence Interval Calculator free?
Yes. It is completely free with no sign-up, no usage limits and no watermark.
Is my data sent to a server?
No. Everything is calculated locally in your browser. Nothing you enter is uploaded, logged or stored.
Does it work on my phone?
Yes. It works in any modern browser on Android, iPhone, iPad, Windows, Mac and Linux — no app needed.