For bettors · 5

Betting calculators

The maths behind odds, staking and value — laid out plainly. Every tool shows its formula and assumptions and predicts nothing.

Odds converter Decimal, fractional, American and implied probability — edit one, the rest follow. Plus payout for your stake. Parlay calculator Combine selections into an accumulator: total odds, payout, profit and the odds it all lands. Expected value (EV) calculator Enter the price and your own probability — see whether the bet is +EV, your edge and the fair odds. Kelly criterion calculator The stake size for long-run bankroll growth at a given edge, with half- and quarter-Kelly options. Arbitrage calculator Best odds per outcome from different books — is there a sure bet, and how to split the stakes.

The other side · for the business Running an operator or affiliate business? A separate set of B2B tools — licence picker and cost, GGR→NGR and margin, commission, LTV, ROI, PSP fees and more. Open B2B tools

What these betting calculators do — and what they don't

Every price a bookmaker offers is a probability with a margin added on top. These five tools take that price apart. The odds converter moves a number between decimal, fractional, American and implied-probability form and shows the payout on your stake. The parlay calculator multiplies legs into a combined price and the rough chance the whole ticket lands. The EV calculator compares the price to your own probability estimate and tells you whether the bet is positive expected value. The Kelly calculator turns an edge into a stake size for long-run bankroll growth. The arbitrage calculator checks whether prices from different books cover every outcome for a locked-in profit, and splits the stakes.

The margin is always there

Add up the implied probabilities of every outcome in a market and the total comes to more than 100%. That excess — the overround, or vig — is the bookmaker's built-in edge, typically 2–7% on a two-way market and much higher on accumulators and exotic bets. None of these calculators remove it; they make it visible so you can judge whether a price is beatable before you stake anything.

They compute, they do not predict

Every result here follows from the numbers you type in. The EV and Kelly tools depend entirely on your own probability estimate — if that estimate is wrong, a confident-looking output is wrong with it. There are no tips, no model picks and no guarantee of profit. Gambling carries risk; only stake what you can afford to lose, and check the rules in your jurisdiction.

Frequently asked questions

Which betting calculator should I start with?

The odds converter, to get comfortable moving a price between formats and reading its implied probability. Once a price means something to you, the EV calculator is the one that answers the real question — is this bet worth making.

What is implied probability?

The win rate at which a price breaks even: 1 ÷ decimal odds. A price of 2.00 implies 50%, 1.50 implies 66.7%, 5.00 implies 20%. It is not the bookmaker's true estimate — it includes their margin — but it is the bar your own estimate has to clear to have an edge.

Do these tools tell me what to bet on?

No. They have no data feed, no model and no tips. They take the odds and the probabilities you enter and do the arithmetic — conversion, combined price, expected value, stake size, arbitrage split. The judgement about probability stays with you.

Why do accumulator odds get so big so fast?

Legs multiply. Four selections at 1.80 each combine to 1.80⁴ ≈ 10.5, but the chance all four land is roughly 1 ÷ 10.5 ≈ 9.5%. The margin also compounds with every leg, so a long accumulator is one of the worst-value bets on the board even though the payout looks large.

Is arbitrage betting realistic?

The maths is simple; the execution is not. Arbs are small (often under 2%), last seconds, and books actively defend against them — odds move while you place the second leg, stake limits get cut, and accounts that arb consistently get restricted or have bets voided. The calculator shows whether an arb exists and how to split it; whether you can actually get both bets on at those prices is another matter.

What edge do I need for the Kelly stake to be positive?

Your estimated win probability has to be higher than the price's implied probability. If a price implies 45% and you think the real chance is 50%, you have a 5-point edge and Kelly suggests a stake; if you think it is 44%, Kelly says bet nothing. Most people use half or quarter Kelly because a small error in the estimate has a large effect on the recommended stake.

Do the calculators account for bet limits, tax or withdrawal fees?

No. They work with clean stake and odds figures. Betting duty in some countries, a stake cap on a boosted price, or a withdrawal fee all reduce the real return — subtract those yourself when a result looks marginal.

Is anything I enter here saved or shared?

No. Every calculator on this page runs entirely in your browser. Nothing you type is sent to a server or stored, and there are no accounts.