Probability Calculator

  • Confidence Interval for a Proportion Calculator
    Compute a confidence interval for a population proportion from successes and sample size at 90%, 95%, or 99% confidence using the normal (Wald) approximation.
  • One-Sample t-Test Calculator
    Compute the one-sample t-test statistic from the sample mean, population mean, standard deviation, and size. Get t, degrees of freedom, and standard error.
  • Standard Error of the Mean (SEM) Calculator
    Calculate the standard error of the mean (SEM) instantly from the sample standard deviation and sample size using SEM = s / √n.
  • Probability Calculator
    Calculate single-event probability P(A)=favorable/total, plus combined P(A and B), P(A or B), and complement P(not A) for independent events.
  • Normal Distribution Probability Calculator
    Calculate normal distribution probabilities P(X<x) and P(X>x) from a value, mean and standard deviation using the standard normal CDF.
  • Binomial Probability Calculator
    Calculate binomial probability P(X=k) for n trials with success probability p. Get exact, cumulative probabilities, mean, variance and standard deviation.
  • Normal CDF — Probability Less Than Z Calculator
    Compute P(Z < z) = Φ(z), the standard normal cumulative probability below a z-score, plus upper tail and percentile. Optional μ and σ to standardize.
  • Permutations and Combinations Calculator
    Calculate permutations (nPr) and combinations (nCr) instantly. Enter n and r to find how many ways to arrange or choose items, with formulas and examples.
  • Odds to Probability Calculator
    Convert odds (a:b) into a probability and percentage instantly. Supports odds in favor and odds against using P = a/(a+b). Free and accurate.
  • Poisson Probability Calculator
    Calculate Poisson probability P(X=k) from a mean rate λ. Get exact, less-than, cumulative, and at-least probabilities instantly with this free tool.
  • Variance of a Probability Distribution Calculator
    Compute the variance and standard deviation of a discrete probability distribution from outcomes xᵢ and probabilities pᵢ using Var(X)=Σpᵢxᵢ²−(Σpᵢxᵢ)².
  • Probability of At Least One Calculator
    Calculate the probability of at least one success in n independent trials using P = 1 - (1-p)^n. Free, instant, with worked examples.
  • Z-Score Calculator
    Free z-score calculator: find the standardized value of a data point, a sample mean, or a data sample using the population mean and standard deviation.
  • Random Playing Card Generator
    Draw random playing cards from a shuffled deck. Choose with or without replacement, customize ranks, suits and jokers, and pick how many cards to deal.
  • Percentile Calculator (Linear Interpolation Method)
    Find any percentile of a data set using linear interpolation (the same R-7 method as Excel and Google Sheets PERCENTILE / PERCENTILE.INC), with an optional percentile table.
  • Random Number Generator (1 to 100)
    Free random number generator from 1 to 100. Click Pick for a uniform random integer (each number 1% likely), with a running pick counter and Reset.
  • Random Number Generator 1-10
    Generate a random integer from 1 to 10 instantly. Each pick is fair and independent with a 10% chance per number, plus a pick counter and probability breakdown.
  • Random Number and Letter Set Generator
    Generate a random set of numbers or letters from any inclusive range. Control sample size, duplicates, and comma separators. Great for PINs, sampling, and lots.
  • Coin Flipper (Heads or Tails Simulator)
    Free online coin flipper. Simulate 1 to 100,000 fair coin tosses, see each Heads or Tails result, and get exact totals and percentages.
  • Lottery Number Generator
    Generate random quick-pick lottery numbers for Powerball, Mega Millions, EuroMillions, Lotto 6/49, Pick games and more. Force in your favorite numbers.
  • 5-Card Draw Poker Dealer Calculator
    Free 5-card draw poker dealer: shuffle a 52-card deck, deal 1-5 players random hands, auto-rank each hand and pick the winner. No betting.
  • Poker Hand Rankings Evaluator
    Enter any 5 cards and instantly see which poker hand they make, from Royal Flush to High Card, with its rank (1-10) and the key cards explained.
  • Bingo Number Generator
    Free online Bingo caller and number generator. Draw random balls without replacement from 1-75 or 1-90, with B-I-N-G-O letters and a live call board.
  • Odds to Probability Calculator
    Convert "A to B" odds into probability, percent chance, and fractional odds for winning and losing. Supports odds for or against winning.

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