A fast, private toolkit for converting odds, sizing bets with the Kelly criterion, computing expected value and modelling variance. Every result comes with the formula and a chart — and nothing you type ever leaves your device.
No setup, no spreadsheets. Pick a tool, type your own figures, and read the result alongside the working.
Choose from odds conversion, Kelly staking, probability and more — grouped by what you're trying to work out.
Type your odds, probabilities or bankroll. Everything updates instantly, right in the page, as you type.
See the answer, the formula behind it and a chart that makes the maths visual — then check or copy it.
All tools run client-side in your browser. Three are live now; the rest are on the way.
Convert between decimal, fractional, American (moneyline) and implied probability instantly.
Single and combined event probability, odds and complements with step-by-step output.
Compute the EV of a bet or decision from probabilities and payoffs.
Combine multiple selections and see the total odds and payout.
Find the mathematically optimal stake as a fraction of your bankroll.
Estimate the probability of losing your bankroll over a series of bets.
Translate return-to-player into house edge and expected loss per stake.
Model swing ranges and standard deviation across a number of rounds.
nCr, nPr and factorial calculations with the working shown.
Probabilities for dice sums, coin runs and simple random experiments.
Staking the “optimal” Kelly fraction maximises long-run growth, but the ride is brutal. Our calculators don't just hand you a number — they show what it does over time, so you can decide how much variance you can stomach.
“Return to player” sounds generous until you turn it into the edge the house keeps on every wager. These are exact figures for specific bets under standard rules — the same maths that powers our game-math tools.
Blackjack: basic strategy, 6 decks, dealer stands on soft 17, 3:2 payouts. Baccarat: Banker bet, 5% commission. Craps: Pass-line bet. Roulette: single-zero (EU) vs double-zero (US).
French La Partage returns half your even-money stake when the ball lands on zero, halving the edge to exactly 1.35%. Each extra zero pocket is pure house margin.
Good decisions under uncertainty aren't about being certain — they're about being roughly right, again and again. ProbabilityKit turns a gut feeling into an explicit probability, an edge and a stake, so you can see exactly what the maths says before you commit.
Start with a calculator
Most odds calculators are buried in ads, hide the formula and quietly send your numbers to a server. We wanted the opposite: fast, transparent and completely private.
ProbabilityKit is a small set of honest tools. The maths is the product — so we show it, run it entirely in your browser, and never ask you to sign up. If a result looks wrong, you can check the working yourself.
Every calculation happens in your browser. Nothing you type is uploaded, logged or shared — there's no server to send it to.
No loading spinners, no round-trips. Once the page loads, the tools keep working even without a connection.
We show the maths behind every result and chart, so you can check the working — not just trust a black box.
Short, plain-English explainers on how the tools work and who's behind them.
The exact formulas behind each tool — odds conversion, implied probability, Kelly staking and more — written out in full.
Read the methodologyWhy ProbabilityKit exists, what we will and won't do with your data, and the principles behind every tool we build.
About the projectFound a result that looks off, or want a calculator we haven't built yet? Tell us — we read every message.
Get in touchYes. Every tool on ProbabilityKit is free to use, with no account or sign-up required.
No. All calculations run locally in your browser using JavaScript. Nothing you type is sent to a server, stored or shared.
Yes. Every page is responsive and works on mobile, tablet and desktop. Because the maths runs in your browser, the tools also keep working offline once a page has loaded.
No. ProbabilityKit provides neutral mathematical tools for understanding probability and odds. The calculators are educational and make no recommendation to bet or gamble.