Probability Calculator

  • Permutations and Combinations (Sample Selection) Calculator
    Compute combinations, permutations, with/without replacement, factorial, even/odd and circular permutations. All four sample-selection cases in one calculator.
  • Permutations with Replacement Calculator
    Calculate permutations with replacement P^R(n,r) = n^r — the number of ordered sequences of r items drawn from n objects when order matters and repeats are allowed.
  • Combination with Replacement Calculator
    Compute combinations with replacement (multichoose): the number of ways to choose r items from n types, unordered, with repetition allowed. Free, instant.
  • Sample Variance Calculator
    Calculate sample variance (s²) and standard deviation from a data set. Uses the n−1 unbiased formula, with mean and sum of squared deviations.
  • Dating Theory (Optimal Stopping) Calculator
    Use the 37% rule (optimal stopping / secretary problem) to find how many dates to reject before committing. Enter your pool size and get the answer.
  • Poker Pot Odds Calculator
    Calculate poker pot odds and the minimum equity you need to call profitably. Enter the current pot and the bet you must call to get instant percentages.
  • Poker EV Calculator
    Calculate the expected value (EV) of a poker decision from your win probability, the amount you win, and the amount you lose. Free and instant.
  • Fisher's Exact Test Calculator (2x2)
    Compute the exact p-value for a 2x2 contingency table using Fisher exact test. Get the hypergeometric probability and two-sided p-value instantly.
  • Matched Betting Calculator
    Free matched betting calculator. Enter back odds, stake, lay odds and exchange commission to get your optimal lay stake, liability and locked-in profit.
  • Mean Absolute Deviation (MAD) Calculator
    Calculate the Mean Absolute Deviation (MAD) of any data set instantly. Enter your numbers to find the average distance from the mean, plus the mean and count.
  • Two Dice Probability Calculator
    Calculate the probability of rolling a given sum with two six-sided dice. Find exact, less-than, or greater-than odds out of 36 outcomes instantly.
  • Possible Combinations Calculator
    Calculate the number of possible combinations C(n,r) = n!/(r!(n-r)!). Find how many ways to choose r items from n, plus permutations P(n,r).
  • Specificity Calculator
    Calculate specificity (true negative rate) from TN and FP counts. Free, instant Specificity = TN / (TN + FP) calculator with worked example.
  • Sensitivity Calculator
    Calculate sensitivity (true positive rate) from true positives and false negatives. Free online tool for diagnostic tests and ML classifiers.
  • Probability Fraction Calculator
    Calculate probability from favorable and total outcomes. Get the decimal probability, percentage, and odds in favor instantly with this free tool.
  • Permutation with Repetition Calculator
    Calculate permutations with repetition using P = n^r. Enter the number of items (n) and selections (r) to find total ordered arrangements instantly.
  • OR Probability Calculator
    Calculate P(A or B) using the addition rule: P(A) + P(B) − P(A and B). Find the probability that at least one of two events occurs.
  • Permutation without Repetition Calculator
    Calculate permutations without repetition P(n,r) = n!/(n−r)!. Find the number of ordered arrangements when selecting r items from n distinct items.
  • Moneyline Odds Calculator
    Convert American moneyline odds into payout, profit, decimal odds and implied probability. Enter your stake and odds (e.g. +150 or -200) instantly.
  • Fractional Odds Calculator
    Convert UK fractional betting odds (e.g. 5/2) into total payout, profit, implied probability and decimal odds for any stake.
  • False Positive Rate Calculator
    Calculate the false positive rate (FPR) from false positives and true negatives. FPR = FP / (FP + TN) = 1 - specificity. Free online tool.
  • DnD Dice Roller Calculator
    Roll any DnD dice combination (XdY) plus a modifier. Get your total, the dice sum, averages, and min/max possible outcomes instantly.
  • Decimal Odds Calculator
    Convert decimal odds to payout, profit and implied probability. Enter your stake and the decimal odds to see your potential winnings instantly.
  • D20 Dice Roller Calculator
    Roll one or more 20-sided dice (d20) online with an optional modifier. Instant random results for D&D, RPGs, and tabletop games.

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