Confidence Interval Calculator
x̄ ± critical × SE. Choose z or t based on whether σ is truly known.
95% confidence interval
[39.0128, 44.9872]
- Critical value used
- 2.0452
- Margin of error
- ±2.9872
How the Confidence Interval Calculator works
The calculation follows the standard method used across the US — no shortcuts, no hidden assumptions. Here is exactly what happens behind the scenes:
Frequently Asked Questions
How does the Confidence Interval Calculator work?
Enter your numbers above and results update instantly using standard formulas, computed entirely on your device.
Is the Confidence Interval Calculator free to use?
Yes — completely free with no signup required, and it works on phones, tablets, and desktops.
Related Calculators
Sample Size Calculator
How many survey responses do you need? Compute n from confidence level, margin, and population.
Math
P-value Calculator
Convert test statistics to p-values: normal z, Student t, chi-square, and F distributions with tail choice.
Math
Statistics Calculator
Complete descriptive statistics: quartiles, IQR, skewness hints, variance, SD, SEM.
Math