How to arbitrage bet, step by step

In short: Find two books pricing opposite sides of a market so far apart that their implied probabilities add up to less than 100%. Stake each side in proportion so both results pay the same — the payout is then larger than your total stake whichever side wins.

Step by step

  1. 1

    Find the two prices

    Compare the best price on each side across books. Convert each to implied probability (1 ÷ decimal odds).

  2. 2

    Check the sum

    If the two implied probabilities add up to under 100%, it is an arbitrage. 100% minus the sum, roughly, is the margin.

  3. 3

    Split the stake

    Stake on each side = total × that side's implied probability ÷ the sum. Both sides then return the same amount.

  4. 4

    Confirm both prices on the betslips

    Open both books. If either price has moved, recompute.

  5. 5

    Place the likelier-to-move leg first

    Usually the softer book's price — the reason the arbitrage exists — then the other leg straight away.

  6. 6

    Check settlement rules

    Make sure both books settle overtime, voids and player withdrawals the same way.

Worked example: a two-book arbitrage

Book A offers Team X at +105 (decimal 2.05). Book B offers Team Y at +102 (decimal 2.02).

Implied: 1 ÷ 2.05 = 48.78% and 1 ÷ 2.02 = 49.50%. Sum: 98.29%.

With $1,000: $496.31 on Team X and $503.69 on Team Y.

Either result returns $1,017.44 — a locked $17.44, or 1.74%, if both bets stand at those prices.

Arbitrage with Kalshi or Polymarket as one leg

Prediction markets price a contract in cents that pays $1 if it wins. A YES at 45¢ is an implied 45%, the same as decimal odds of 2.22 — before fees.

Both charge a taker fee that depends on the price: Kalshi 0.07 × contracts × price × (1 − price), rounded up to the cent, and Polymarket US 0.06 × contracts × price × (1 − price), per each venue's published schedule. Kalshi charges half on MLB. Always include the fee before you call it an arbitrage.

Example: buy 400 Team X YES contracts on Kalshi at 45¢ = $180.00. Fee: 0.07 × 400 × 0.45 × 0.55 = $6.93. At a sportsbook, bet $209.52 on Team Y at -110 (decimal 1.9091), which returns about $400. Total outlay $396.45; either result returns about $400 — about $3.55 locked. Without the fee it would have looked like $10.48: the fee took two-thirds of the margin.

Exchanges and prediction markets match you against other traders, so there is no house limiting winning customers. Liquidity is the limit instead: check there are enough contracts at your price.

How sportsbooks limit arbitrage bettors — and how to live with it

Sportsbooks may cut the maximum stake of an account they see winning from price differences. That is allowed by their terms, and it is the main practical limit on arbitrage.

  • Use exchanges and prediction markets for one leg where you can; they do not limit winners the same way.
  • Spread your volume across many books rather than concentrating it.
  • Take the promotions books offer — that is ordinary use of an account.
  • Never use someone else's account or open a second one at the same book; that breaks the terms and can cost you your balance.
  • Only bet where you are legally allowed to, from where you are.

Tools for this

Frequently asked questions

How do you arbitrage bet?

Find two books whose prices on opposite sides add up to under 100% implied probability, then stake each side in proportion so both results pay the same amount.

How do you arbitrage bet on Kalshi?

Buy the contract for one side on Kalshi and bet the other side at a sportsbook, sized so both results pay the same. Include Kalshi's fee, which can remove most of a thin margin.

How do you arbitrage bet on Polymarket?

The same way: one side on Polymarket, the other at a sportsbook or another venue. Polymarket US charges 0.06 × contracts × price × (1 − price) as a taker fee, so price it in first.

How do you arbitrage bet without getting limited?

You cannot rule it out at sportsbooks. Using exchanges and prediction markets for one leg, spreading volume across books and taking promotions all help. Never use another person's account.

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