How to use the odds calculator
- Convert & payout: type a price in any format (American, decimal, fractional or implied probability) and the other three follow, with the payout and profit for your stake.
- Parlay: enter each leg's odds and, once games finish, mark legs won, pushed or lost. You get the combined odds, the payout and the implied chance of every leg winning.
- Each way & Lucky 15: settle an each way single or multiple, or a full-cover bet such as a Yankee or Lucky 15, with each selection marked won, placed, lost or a non-runner and the place terms of the race.
- Vig & fair odds: enter every outcome of one market to see the bookmaker's margin and the fair, no-vig odds.
- Arbitrage & hedge: split a stake across outcomes at different books, or work out how much to bet on the other side of an open bet.
- Kalshi & Polymarket: turn a prediction-market contract price into odds with the platform's trading fee taken off, and compare it with a sportsbook price. The Kalshi and Polymarket converter explains the fees.
Choose how you type odds for the lists under Enter odds as; switching format rewrites what you've typed. Share result saves everything in the link, and nothing is sent anywhere.
American, decimal and fractional odds
They are three ways of writing the same price. Decimal odds (common in Europe, Canada and Australia) are the total return for each 1 staked, stake included: 2.50 returns 25 on 10. American odds are based on 100: +150 means a 100 stake wins 150; −110 means you stake 110 to win 100. Fractional odds (UK and Ireland) are profit over stake: 3/2 wins 3 for every 2, and evens is 1/1.
- American to decimal:
+A → 1 + A/100,−A → 1 + 100/A. - Decimal to American: at 2.00 or more
+(d − 1) × 100, below 2.00−100 / (d − 1). - Fractional to decimal:
n/d → 1 + n/d. A decimal price quoted to two places is an exact fraction of 100, so 4.33 shows as 333/100, with the traditional price a bookmaker would print next to it (≈ 10/3).
Implied probability and the break-even rate
Implied probability is 1 ÷ decimal odds: 2.50 implies 40% and −110 implies 52.38%. It is also the share of bets you'd need to win just to break even at that price, which is why −110 on both sides of a game is hard to beat over time: you have to win 52.4% of your picks, not 50%.
The vig and fair odds
Add up the implied probabilities of every outcome in a market and you get more than 100%. The extra is the overround; the bookmaker's margin (the vig or juice) is 1 − 1 / total, what the book keeps from a balanced set of bets. Dividing each implied chance by the total spreads the margin back out and gives fair, no-vig odds, a better estimate of the true chances. That is the proportional method; the power and Shin methods assume longshots carry more of the margin and give slightly different fair prices.
Parlays
A parlay (an accumulator in the UK) multiplies the decimal odds of its legs, so the payout grows fast, and so does the margin: each leg's vig compounds. With a 4.55% margin on every leg, a 3-leg parlay pays about 87% of what fair odds would, and a 6-leg one about 76%. Parlays with a push usually drop that leg and pay on the rest.
Arbitrage and hedging
If different books price the same game so that the best odds on each side add up to less than 100% implied, staking every side in proportion to its implied chance wins the same amount whichever outcome happens, if every bet is accepted and stands. Prices move quickly and books may cancel bets or limit accounts, so the edge is often smaller in practice. A hedge is the same idea for a bet you've already made: bet the other side to lock in a profit or cap a loss.
Keep it a game
Betting is entertainment with a built-in cost: the margin means the average bettor loses over time. Set a budget you can afford to lose, don't chase losses, and check that betting is legal where you are. If it stops being fun, free and confidential help is available:
- United States: National Problem Gambling Helpline, 1-800-MY-RESET (1-800-697-3738), call, text or chat. ncpgambling.org
- United Kingdom: National Gambling Helpline (GamCare), 0808 8020 133, 24 hours. gamcare.org.uk
- Australia: Gambling Help Online, 1800 858 858, 24 hours. gamblinghelponline.org.au
- Canada: Responsible Gambling Council, helplines for each province. responsiblegambling.org
- Any country: Gambling Therapy (Gordon Moody), free online support in many languages. gamblingtherapy.org
For games of pure chance, the dice roller shows exact probabilities for any dice, and Super Bowl squares sets up a friendly pool for the game.
Helplines checked September 2026. This calculator does maths only; it is not betting advice and has no links to sportsbooks.