Loading the page…
Probability, combinatorics, paradox simulators, and confusion-matrix metrics for the data-curious.
Tap any card to open its calculator page.
Calculate the probability of an event given favorable and total outcomes
Apply Bayes' theorem to find conditional probabilities
Calculate accuracy, precision, and recall from a confusion matrix
Calculate sample proportion and confidence interval for proportions
Calculate the number of combinations C(n, r) from n items choose r
Calculate the number of ordered permutations P(n, r)
Calculate the expected value (mean) of a probability distribution
Calculate P(A|B) from the joint probability P(A∩B) and P(B)
Convert decimal betting odds to implied probability percentage
Calculate the jackpot odds and match probabilities for a lottery draw
Convert probability to fractional, decimal, and American odds formats
Calculate the number of possible passwords and entropy bits for a given charset and length
Calculate relative risk and odds ratio from a 2×2 contingency table
Calculate sensitivity, specificity, PPV, and NPV from a confusion matrix
Apply Chebyshev's theorem to find the minimum proportion within k standard deviations
Calculate the probability of getting exactly k heads in n coin flips
Calculate the probability of rolling a specific sum with n dice
Calculate the average, min, max, and variance for rolling n dice
Calculate the union and intersection probabilities of three independent events
Calculate absolute risk, relative risk reduction, and number needed to treat
Calculate post-test probability using sensitivity, specificity, and prevalence
Calculate the probability that at least two people in a group share a birthday
Calculate roulette bet payouts and house edge for different bet types
Calculate the probability of getting a streak of k heads in n coin flips
Roll any number and type of dice and see the results instantly
Flip multiple coins and track heads and tails results
Generate random numbers within a custom range
Compute all classification metrics from a 2×2 confusion matrix
Simulate the Monty Hall problem and compare switch vs stay win rates
Explore how rare conditions lead to high false-positive rates in testing
Explore how two losing games can combine to produce a winning strategy
Explore Bertrand's box paradox and conditional probability
Explore Bertrand's paradox about the probability of a random chord
Explore the boy-or-girl paradox and how context changes probability
Explore the two envelopes paradox and why switching seems to always win
All 570 calculators in your pocket. Offline-ready, no ads, no trackers. iOS and Android apps land soon — get notified when they ship.