Confidence Interval Calculator

Estimate the true population parameter with confidence. Select what you are trying to measure (a mean or a proportion), enter your data, and calculate your margin of error and confidence bounds.

How to use this calculator

1. Choose your metric: Select whether you want to calculate the confidence interval for a Mean (an average, like height or test scores) or a Proportion (a percentage, like the win rate or voting preference).
2. Enter your data:
   • For Means: You can either paste your raw data directly, or enter your summary statistics (sample mean, standard deviation, and sample size) if you already calculated them.
   • For Proportions: Enter the total number of trials/observations ($n$) and the number of “successes” ($x$).
3. Select your Confidence Level: 95% is the gold standard for most scientific and business research.

Understanding Your Results

A confidence interval gives you a range of values that is likely to contain the true, unknown population parameter you are trying to measure.

• Point Estimate: Your best guess for the population parameter, based purely on your sample (e.g., your sample mean or sample proportion).
• Margin of Error: The amount of random sampling error around your point estimate. A larger sample size ($n$) will decrease your margin of error, making your estimate more precise.
• Lower & Upper Bounds: The actual range of your interval.
• Interpretation: If you calculate a 95% confidence interval for a mean, it means that if you were to repeat this exact experiment 100 times, you would expect 95 of the calculated intervals to contain the true population mean.