ProbaLab hosts 22 calculators you can actually use: dice matrices, Bayesian diagnostics, Monte Carlo portfolios, PERT critical paths, blackjack bust advisors, VaR, Kelly sizing, queue waits and more. Each one ships a chart, a method note, and a "limitations" section so you know when not to trust the answer.
Every tool ships with a full method note, a chart and a "limitations" section. No black boxes, no "Try our premium" paywalls.
All computation runs in your browser. The server only serves HTML and CSS. We do not log inputs.
Every calculator ends with "When not to trust this" so you stop misusing statistical toys.
Pick the closest match to your decision — each tool documents its assumptions in plain English before you start.
Roll any number of dice, get the full probability mass table, distribution curve and skewness.
Streak math, Martingale ruin simulator, and the St. Petersburg paradox explained.
Beyond the classic "23 people" trick: collision curve, near-miss and recommended action thresholds.
Full enumeration for 5/6/7-card hands — strength score, hand-rank histogram, "out" calculator.
PPV / NPV / likelihood ratios with a slider that visualises the base-rate fallacy live.
Compare banners, simulate pity counters, and convert expected drops to dollar cost per pull.
Powerball, Mega Millions, EuroMillions: hypergeometric probabilities with EV vs annuity.
Sample size, MDE, frequentist significance and Bayesian posterior — same data, four lenses.
Dealer bust probability by upcard, basic-strategy suggestion and counter-friendly EV estimate.
Urn problems, MTG deck draw, quality-control sampling, and inventory depletion probability.
Effective APR including fees, early-payoff savings, refinance break-even month.
Geometric Brownian motion with correlation, rebalancing and withdrawal sequence risk.
Historical / parametric Value at Risk, CVaR, and rolling drawdown visualisation.
Full / fractional Kelly, multi-bet correlation, and bankroll-growth path simulator.
Finds the stack order that maximizes effective discount and warns about minimum-spend traps.
Win / draw / loss from ELO ratings with best-of-N series probability and upset curves.
Surface-adjusted Elo → set-by-set probability, tiebreaks and live game-state updates.
Critical-path visualisation with optimistic / most-likely / pessimistic estimates.
Series / parallel systems, redundant components, MTBF and steady-state availability.
Erlang-C for call centers, clinics, and checkouts; server-count optimizer for SL targets.
Historical probability of rain / temperature thresholds for any date — wedding, race day, hike.
Sample size for a given margin of error, finite-population correction and stratified samples.
Every ProbaLab tool shares three rules. They are the difference between a calculator and a toy.
For the classic "roll 3d6 and guess the most likely sum", the answer is 10 or 11 at 12.5% each — not the naive mean of 10.5. The full mass function makes the symmetry visible.
| Sum | Counts | P |
|---|---|---|
| 3 | 1 | 0.46% |
| 7 | 15 | 6.94% |
| 10 | 27 | 12.50% |
| 11 | 27 | 12.50% |
| 14 | 1 | 0.46% |
Counted via stars-and-bars; 216 equally-likely ordered triples.
ProbaLab is a small, ad-funded calculator lab run by an independent author with a background in statistics and operations research. The aim is to give you tools that are at least one notch deeper than the ones you find on the first page of a search result. Each calculator includes its math, its limits, and a chart — so you can defend the result to a colleague.
Suitable for: students of statistics, traders sizing positions, PMs scoping experiments, boardgame designers playtesting, operations teams sizing headcount, and curious laypeople sanity-checking a viral claim. Not suitable for: regulated financial, medical or structural decisions — see the disclaimer below.
Effective date: 2026-09-17. Last updated: 2026-09-17.
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All calculators on ProbaLab are provided for educational and informational purposes only. The math is correct under the assumptions stated on each page, but real decisions depend on inputs the calculator does not see.
By using this site you agree that the author bears no liability for losses arising from use of the calculators.