Free Statistics & Probability Calculators

Standard Deviation Calculator

Calculate standard deviation, variance, and other statistics for a dataset.

Z-Score Calculator — Standard Score & Percentile

Calculate z-score, percentile rank, and p-values from any data point, mean, and standard deviation. Includes reverse calculation and step-by-step solutions.

Probability Calculator — Events

Calculate single event, multiple event, conditional, and complementary probabilities.

Correlation Coefficient Calculator

Calculate Pearson r and Spearman ρ between two datasets with p-value, R², regression line, and scatter plot.

Linear Regression Calculator

Find the best-fit line (y = mx + b) using least squares regression.

Binomial Distribution Calculator

Calculate binomial probability P(X=k), CDF, mean, variance, and distribution statistics for any n and p. Includes bar chart and full probability table.

Poisson Distribution Calculator

Calculate Poisson probabilities for rare event modeling.

Chi-Square Calculator

Perform chi-square goodness-of-fit and independence tests with p-value, critical value, effect size (Cramér's V, Cohen's w), Yates' correction, standardised residuals, and chi-square distribution curve. Supports 2–5×2–5 contingency tables with real-world presets.

Confidence Interval Calculator — Mean & Proportion

Calculate confidence intervals for means (z and t-test) and proportions (Wald and Wilson). Shows margin of error, critical value, SE, step-by-step working, and a visual bell curve diagram.

Sample Size Calculator

Calculate the required sample size for surveys and experiments.

Percentile Calculator — Rank & Value

Find percentile ranks and values from a dataset.

ANOVA Calculator — One-Way with p-value & Effect Size

Perform one-way ANOVA with up to 6 groups. Shows the full ANOVA table, exact p-value, effect size η², group statistics, and a significance verdict — no F-table look-up needed.

Bayes' Theorem Calculator

Calculate posterior probability P(A|B) from prior, sensitivity, and false positive rate. Includes natural frequencies, Bayes factor, and step-by-step derivation.

T-Test Calculator — One-Sample

Perform a one-sample t-test to determine if a sample mean differs significantly from a known value.

Variance Calculator — Population & Sample

Calculate population variance and sample variance from a dataset with step-by-step workings.

Quartile Calculator — Q1, Q2, Q3 & IQR

Calculate Q1, Q2 (median), Q3, interquartile range (IQR), and detect outliers from data.

Frequency Distribution Calculator — Tables & Charts

Build grouped or ungrouped frequency distribution tables from raw data. Shows relative and cumulative frequencies, modal class, estimated mean and standard deviation, and a bar chart.

Geometric Mean Calculator — CAGR & Rates

Calculate geometric mean for growth rates, investment CAGR, and multiplicative data. Compare AM, GM, and HM with warnings for zeros and negatives.

Moving Average Calculator — SMA & EMA

Calculate simple moving average (SMA) and exponential moving average (EMA) for time series data.

Effect Size Calculator — Cohen's d, η² & r

Calculate Cohen's d, Hedges' g, Glass's Δ, r, and η² effect sizes from means, t-statistics, F-statistics, or correlation r. Includes 95% CI, power, and required sample size.

P-Value Calculator — Z, T, Chi-Square & F

Calculate the exact p-value from a z-score, t-statistic, chi-square statistic, or F-statistic. Supports one-tailed and two-tailed tests with significance interpretation.

Mean, Median & Mode Calculator

Calculate the mean, median, mode, range, variance, standard deviation, quartiles, and IQR for any dataset. Detects outliers, shows sorted data, and supports both population and sample statistics.

Normal Distribution Calculator — PDF, CDF & Inverse

Compute exact probabilities for any normal distribution: P(X < a), P(X > a), P(a ≤ X ≤ b), inverse CDF (quantile), and PDF at a point. Works with standard normal (μ=0, σ=1) and custom parameters. Bell curve visualization included.