Confidence Interval Calculator
Last updated: July 2026
Estimate a mean confidence interval from a sample mean, standard deviation, sample size and critical value.
Margin of error
—
- Lower confidence limit: —
- Upper confidence limit: —
- Standard error: —
- Interval width: —
On this page
Quick summary: Estimate a mean confidence interval from a sample mean, standard deviation, sample size and critical value. Enter the requested values, calculate, review the result, and compare more than one realistic scenario before making a decision.
Read the complete guide
What this calculator estimates
Estimate a mean confidence interval from a sample mean, standard deviation, sample size and critical value. It is designed for fast planning and comparison in the United States. The output is an estimate, not a binding quote, approval, tax determination, insurance offer, legal conclusion, medical recommendation or professional advice.
How to use it
Enter the requested values using a single consistent time period and currency. Select Calculate, review the headline result and supporting figures, then change one assumption at a time to compare another scenario.
How the calculation works
The margin of error equals the critical value multiplied by the sample standard deviation divided by the square root of sample size.
Important limitations
This normal-approximation interval may be unsuitable for small or nonrepresentative samples.
Frequently asked questions
Is the result exact?
No. It is a planning estimate based on the assumptions entered.
Can I compare different scenarios?
Yes. Change one input at a time so you can see which assumption changes the result.
Does the calculator store my inputs?
The calculation runs in the browser and does not require an account. Avoid entering unnecessary confidential information.