How to find the upper and lower limits of a confidence interval in excel

This formula creates an interval with a lower bound and an upper bound, which likely contains a population parameter with a certain level of confidence:

Confidence Interval  = [lower bound, upper bound]

This tutorial explains how to calculate the following confidence intervals in Excel:

1. Confidence Interval for a Mean

2. Confidence Interval for a Difference in Means

3. Confidence Interval for a Proportion

4. Confidence Interval for a Difference in Proportions

Let’s jump in!

Example 1: Confidence Interval for a Mean

We use the following formula to calculate a confidence interval for a mean:

Confidence Interval = x  +/-  z*(s/√n)

where:

• x: sample mean
• z: the chosen z-value
• s: sample standard deviation
• n: sample size

Example: Suppose we collect a random sample of turtles with the following information:

• Sample size n = 25
• Sample mean weight x = 300
• Sample standard deviation s = 18.5

The following screenshot shows how to calculate a 95% confidence interval for

how to do 95 confidence interval in excel

how to do a 99 confidence interval in excel