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Arbitrage Betting Calculator

Enter the best odds on each outcome, from bookmakers, exchanges or Polymarket. The calculator checks whether they add up to a guaranteed profit after commission and fees, and how to split your stake so every outcome pays the same.

$
Outcome 1
Outcome 2
$
Implied total
98.70%
Guaranteed profit
$13.15
Return on stake
1.31%

Arbitrage: whichever outcome wins, you get the same payout.

Odds after feesStakePayout if it wins
Outcome 12.200$460.52$1,013.15
Outcome 21.878$539.481013 shares$1,013.15

Odds after fees: bookmaker odds stay as they are; exchange odds become 1 + (odds − 1) × (1 − commission); a Polymarket price p becomes 1 ÷ (p + feeRate × p × (1 − p)), the taker fee on a market buy. An arbitrage exists when the sum of 1 ÷ odds after fees is below 100%. Each stake = total stake × (1 ÷ its odds) ÷ that sum, so every outcome pays total stake ÷ sum.

How to Use the Arbitrage Calculator

  1. Choose 2 outcomes (tennis, basketball, a Yes/No market) or 3 outcomes (home, draw, away).
  2. For each outcome, choose where the best price is. Enter bookmaker odds (commission 0), exchange odds with the commission rate, or a Polymarket price (the best offer) and its fee.
  3. Enter your total stake. The calculator shows whether there’s an arbitrage, the guaranteed profit, and the stake for each outcome.

How Arbitrage Works

Each price implies a probability. Bookmakers build a margin in, so one bookmaker’s prices always add up to more than 100%. But different venues disagree. Take the best price on every outcome from different places, and sometimes the total drops below 100%. Back every outcome in the right proportions and you’re paid the same whichever wins.

Example. A bookmaker offers 2.20 on Player A. Polymarket’s best offer on Player B is $0.52, and the taker fee on most sports adds 0.05 × 0.52 × 0.48 ≈ $0.0125 a share, an effective price of $0.5325.

  • Implied total: 1 ÷ 2.20 + 0.5325 = 45.45% + 53.25% = 98.70%
  • On $1,000: $460.52 on Player A at the bookmaker, $539.48 on Player B on Polymarket (1,013 shares)
  • Either result pays about $1,013.15: a guaranteed $13.15 (1.3%)

Things That Break an Arbitrage

  • Different rules. Both legs must settle on exactly the same thing. Check extra time, retirements in tennis, void rules and dead heats.
  • Prices move. Place the leg most likely to move first. On Polymarket, the best offer may only cover a few hundred dollars; a bigger order fills at worse prices.
  • Fees and commission. Polymarket’s taker fee is included above. A limit order that rests on the book pays no fee, but it may not fill before the price moves.
  • Account limits. Bookmakers routinely limit customers who arb. I’ve been limited or banned by 40 to 50 sites, mostly for value betting and arbing. Banned for winning explains why, and why an exchange like Polymarket doesn’t do it.

Frequently Asked Questions

How do you calculate an arbitrage bet?
Convert each outcome's best odds to an implied probability (1 ÷ decimal odds) and add them up. If the total is below 100%, there's an arbitrage. Stake each outcome in proportion to its implied probability: stake = total stake × (1 ÷ odds) ÷ the total. Every outcome then pays total stake ÷ the total.
Is arbitrage betting legal?
Arbitrage betting is generally legal, since you're just placing ordinary bets. But bookmakers dislike it and often limit or close the accounts of customers they identify as arbers. Polymarket isn't the house, so it has no reason to limit winning traders.
Can you arb between Polymarket and a sportsbook?
Yes. Polymarket's prices have no built-in vig, so its price on one side is often better than a bookmaker's. When a bookmaker's odds on the other side are out of line, the two together can add up to less than 100%. Include Polymarket's taker fee, which the calculator does.
Why does my arbitrage disappear when I place the bets?
Odds move, and the best price may only be good for a small amount. Bookmakers can cut your maximum stake or void a bet placed at an obvious mistake price. Place the leg most likely to move first, and on Polymarket check that the order book has enough depth at your price.
What is a good arbitrage percentage?
Most real arbitrages lock in 1% to 3% of the total stake. Bigger numbers usually mean a mistake price, a stale line, or two markets with different rules (for example, one settles on 90 minutes and the other includes extra time).