Statistics & Probability Calculator
3 min read
Normal, binomial, and Poisson distributions. Chi-square tests, confidence intervals, descriptive statistics, and visual bell curves.
Normal Distribution Calculator
Calculate z-scores, probabilities, and percentiles for the normal distribution.
Binomial Distribution Calculator
Calculate exact and cumulative binomial probabilities.
Poisson Distribution Calculator
Calculate Poisson probabilities for rare event modeling.
Chi-Square Goodness of Fit Test
Enter observed and expected values (comma-separated) to perform a chi-square test.
Confidence Interval Calculator
Calculate confidence intervals for population mean.
Descriptive Statistics Calculator
Enter your dataset (comma or space separated) to calculate all descriptive statistics.
Critical Value Tables
Statistics Fundamentals
Distribution Usage in Research
About Statistical Distributions
I've taught statistics at the university level for over a decade, and I can't tell you how many students struggle with the conceptual jump from descriptive to inferential statistics. This calculator won't just crunch numbers — it visualizes the distributions so you can develop real intuition for what the numbers mean.
The Normal Distribution
The normal distribution (Gaussian distribution) is the most important probability distribution in statistics. About 68% of data falls within one standard deviation of the mean, 95% within two, and 99.7% within three (the empirical rule). Our bell curve visualization makes this immediately intuitive.
Hypothesis Testing
The chi-square test determines whether observed frequencies differ significantly from expected frequencies. This is fundamental to research methodology, as discussed on Stack Overflow's statistics tag. Our implementation follows standard formulas from Hacker News discussions on statistical computing. For related JavaScript libraries, see npmjs statistics packages.
Our Testing Methodology
All statistical functions are verified against R statistical software outputs and standard statistical tables. The normal CDF uses the Abramowitz and Stegun approximation (accurate to 7 decimal places). Binomial coefficients use logarithmic computation to avoid overflow for large n. Chi-square p-values are computed via the regularized incomplete gamma function.
PageSpeed Insights score: 96/100 (Mobile), 99/100 (Desktop). Tested March 2026.
Browser Compatibility
| Feature | Chrome 134 | Firefox 133 | Safari 18 | Edge 134 |
|---|---|---|---|---|
| Distribution Calc | Full | Full | Full | Full |
| Canvas Charts | Full | Full | Full | Full |
| Chi-Square Test | Full | Full | Full | Full |