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Arbitrage Calculator: Calculate Sports Betting Arb Opportunities

Last Updated: March 4, 2026

Arbitrage betting captures guaranteed profit by exploiting odds differences between sportsbooks. Enter odds from two books into the calculator above, and it computes whether an arb exists, the exact stake to place on each side, and your guaranteed profit regardless of the outcome.

How Do You Use the Arbitrage Calculator?

The calculator requires three inputs: the odds for Outcome A from one sportsbook, the odds for Outcome B from another sportsbook, and your total investment amount. It accepts American, decimal, and fractional formats.

Step-by-step:

  1. Enter the best odds you found for Outcome A (e.g., Lakers +165 from Book A)
  2. Enter the best odds for Outcome B (e.g., Celtics -150 from Book B)
  3. Enter your total investment amount
  4. The calculator returns whether an arb exists, the margin percentage, the exact dollar amount to place on each side, and the guaranteed profit for both outcomes

The tool converts everything to decimal odds internally before running the arb formula. If you need to manually convert between formats first, use the odds converter.

How Do You Understand the Arbitrage Results?

The core output is the arb percentage — the sum of implied probabilities across both sides. Below 100% means profit. Above 100% means the vig exceeds the price discrepancy, and no arb exists.

Result FieldWhat It MeansExample
Arb PercentageSum of implied probabilities97.73%
Arb MarginGuaranteed profit percentage2.27% (100% - 97.73%)
Stake AAmount to place on Outcome A$386.10
Stake BAmount to place on Outcome B$613.90
Profit (A wins)Net if Outcome A wins$23.17
Profit (B wins)Net if Outcome B wins$23.37

The slight difference between profit scenarios is due to rounding. Both outcomes yield approximately the same return — that is the defining feature of an arb.

How Does an Arbitrage Calculation Work in Practice?

Consider an NBA moneyline where Book A offers Lakers at +165 (decimal 2.65) and Book B has Celtics at -150 (decimal 1.667).

Implied probabilities:

  • Lakers: 1 / 2.65 = 37.74%
  • Celtics: 1 / 1.667 = 59.99%
  • Combined: 97.73%

Since 97.73% is below 100%, the arb margin is 2.27%. On a $1,000 total investment, the calculator allocates $386.10 to the Lakers and $613.90 to the Celtics. If the Lakers win, you collect $1,023.17. If the Celtics win, you collect $1,023.37. Either way, you profit roughly $23.

This is identical to the math covered in our full arbitrage betting guide, but the calculator eliminates the manual arithmetic. The key skill is finding the odds discrepancy — the calculator handles the rest.

Why Does Arbitrage Matter for Prediction Markets?

Prediction markets create arb opportunities when the same event trades at different prices across platforms. The Odds Reference dashboard tracks contract prices across Polymarket, Kalshi, and other platforms. When a YES contract costs $0.44 on one exchange and the corresponding NO contract costs $0.53 on another, the combined cost of $0.97 guarantees a $0.03 profit per contract pair.

Prediction market arbs differ from sportsbook arbs in two important ways. First, platforms generally do not limit accounts for arbing — there is no equivalent of the sportsbook account restriction that makes traditional arbing unsustainable. Second, you can exit positions before settlement by selling contracts back to the market, adding flexibility that sportsbook bets do not offer.

Our data shows that cross-platform prediction market arbs appear more frequently than sportsbook arbs because prices are set by individual traders rather than professional bookmakers. The tradeoffs are thinner liquidity and platform fees that reduce net margin. Compare fee structures across platforms on our sportsbook and platform comparison page.

Key Takeaways

  • An arb exists when combined implied probabilities across books total less than 100% — the calculator checks this instantly
  • Stake allocation must be proportional to the inverse of each side’s odds to equalize profit across outcomes
  • Most real arbs are 1-4% and close within minutes, so speed from identification to execution is critical
  • The same arb math applies to prediction markets, where cross-platform price differences create similar guaranteed-profit windows
  • Always verify that both lines are still available before placing stakes — if one side moves, the arb may vanish

Frequently Asked Questions

How do you calculate arbitrage in sports betting?
Convert both sides' odds to decimal format, then add the reciprocals: (1/Odds A) + (1/Odds B). If the total is less than 1.00, an arbitrage opportunity exists. Your guaranteed profit margin equals 1 minus that total. The calculator above handles the conversion and stake math automatically for any odds format.
How do I know if an arbitrage opportunity exists?
An arb exists when the combined implied probability across two or more sportsbooks totals less than 100%. This means the books disagree enough on the pricing that you can back all outcomes and still profit. The wider the gap below 100%, the larger your guaranteed margin. Most real arbs fall in the 1-4% range.
Can you arb prediction markets?
Yes. When the same event is listed on multiple prediction market platforms at different contract prices, you can buy opposing positions whose combined cost is less than the guaranteed $1 payout. For example, YES at $0.44 on one platform and NO at $0.53 on another costs $0.97 for a guaranteed $1 return — a 3.1% risk-free profit.
What is a realistic arb margin?
Most actionable arbs in legal U.S. sportsbooks range from 1% to 4% and close within minutes. Larger margins (5%+) are rare and often indicate stale lines or pricing errors that books may void. In prediction markets, cross-platform arbs of 2-5% appear more frequently because prices are set by traders, not bookmakers.