How to Use Excel to Calculate a Confidence Interval

1. Enter the alpha value in cell A1. The alpha value equals 1 minus the confidence level. For example, if your confidence level equals 96 percent, you would enter 0.04 in cell A1.
2. Enter the standard deviation in cell A2. For example, if your standard deviation equals 1.1, enter '1.1' in cell A2.
3. Enter the sample size in cell A3. For example, if your sample size equals 3,000, enter '3,000' in cell A3.
4. Enter 'CONFIDENCE(A1,A2,A3)' in cell A4 and Excel will display the confidence interval. In this example, Excel will display '0.041245769' meaning your confidence interval equals plus or minus 4.12 percent.