Probability Calculator

  • Binomial Probability Calculator P(X=k)
    Calculate the exact binomial probability P(X=k) for n trials with success probability p. Free online tool using the binomial formula with worked examples.
  • Binomial Confidence Interval Calculator
    Compute a Wilson score confidence interval for a binomial proportion. Enter successes, trials and a confidence level to get the lower and upper bounds.
  • Critical t Value Calculator
    Find the critical t value for any significance level (α) and degrees of freedom. Supports one-tailed and two-tailed tests using the t distribution.
  • Critical Z Value Calculator
    Find the critical z value (z*) from any confidence level using the inverse normal CDF. Supports two-tailed and one-tailed tests. Free and instant.
  • Spearman's Rank Correlation Calculator
    Calculate Spearman's rank correlation coefficient (ρ) from paired X and Y data. Handles ties, shows Σd² and n. Free statistics tool.
  • Sample Size Calculator for a Mean
    Calculate the required sample size to estimate a population mean within a target margin of error and confidence level using n = (z·σ/E)².
  • P-Value from t-Score Calculator
    Convert a Student's t-score and degrees of freedom into a p-value. Supports one-tailed and two-tailed tests with exact incomplete-beta computation.
  • Sample Size Calculator (Proportion)
    Calculate the required survey sample size for estimating a proportion at a given confidence level and margin of error using n = z²·p(1−p)/E².
  • Cohen's d Effect Size Calculator
    Calculate Cohen's d effect size from two group means, standard deviations and sample sizes, with pooled SD and a small/medium/large interpretation.
  • Chi-Square Test of Independence Calculator (2x2)
    Run a 2x2 chi-square test of independence online. Enter your contingency table cells to get χ², degrees of freedom, p-value, and significance at α = 0.05.
  • Five-Number Summary Calculator
    Find the five-number summary (minimum, Q1, median, Q3, maximum) plus IQR for any data set. Free online statistics calculator with worked examples.
  • Complement Probability Calculator
    Calculate the complement probability P(A') = 1 − P(A) instantly. Enter the probability of an event and find the chance it does NOT happen.
  • P-Value from Z-Score Calculator
    Convert a Z-score to a P-value for one-tailed or two-tailed hypothesis tests. Uses the standard normal distribution to compute statistical significance.
  • Weighted Mean Calculator
    Calculate the weighted mean (weighted average) from a set of values and their weights. Enter comma-separated values and weights to get the result instantly.
  • Percentile to Z-Score Calculator
    Convert any percentile (0–100) into a standard normal z-score using the inverse normal CDF, z = Φ⁻¹(p). Fast, accurate, and free.
  • Chi-Square Test Statistic Calculator
    Calculate the chi-square (χ²) test statistic from observed and expected frequencies. Free goodness-of-fit calculator with degrees of freedom.
  • One-Sample t-Test Calculator
    Calculate the one-sample t-test statistic from sample mean, hypothesized mean, standard deviation and sample size. Get t, standard error and degrees of freedom.
  • Z-Score to Probability Calculator
    Convert a z-score to a probability using the standard normal CDF. Get left-tail, right-tail, and two-tailed p-values from any z value instantly.
  • Probability Calculator
    Free probability calculator for two independent events. Compute P(A and B), P(A or B), P(neither) and P(not both) instantly from decimal inputs.
  • F1 Score Calculator
    Calculate the F1 score, precision, and recall from True Positives, False Positives, and False Negatives. Free machine-learning classification metric tool.
  • Probability of At Least k Successes (Binomial)
    Calculate P(X ≥ k) for a binomial distribution — the probability of at least k successes in n trials with success probability p. Free, instant, exact.
  • Poker Hand Probability Calculator
    Calculate the probability and odds of being dealt any 5-card poker hand from a standard 52-card deck, from royal flush to high card.
  • Confidence Interval for a Mean Calculator
    Compute a confidence interval for a population mean using the Student-t distribution. Enter sample mean, standard deviation, size, and confidence level.
  • Monty Hall Problem Probability Calculator
    Calculate the Monty Hall problem odds for any number of doors. See why switching wins (d−1)/d of the time and staying only 1/d.

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