Free MLB Arbitrage Finder | Cross-Book Arb Scanner | Mongoose Bets
Arbitrage Calculator
Check whether two sportsbooks' lines form a locked-profit arbitrage. MLB-focused.
Manual arbitrage calculator
Enter American odds from two different sportsbooks for opposite sides of the same market (e.g. Yankees ML at Book A, Red Sox ML at Book B).
Today's live MLB arbs
Live cross-book scanning is temporarily unavailable. The Mongoose Bets frontend currently reads pre-aggregated best-odds for moneyline markets, without the per-book breakdown needed to detect arbs. Use the manual calculator above by entering the best price you see at each of your books.
Future work: expose per-book moneyline odds in the Mongoose Bets Supabase schema so this section can populate automatically.
What is arbitrage betting?
Arbitrage betting (or "arbing") is placing bets on every possible outcome of a market across different sportsbooks so that, regardless of which side wins, you lock in a guaranteed profit. The math works when the sum of the best implied probabilities across books is less than 100%. The gap below 100% is your guaranteed return.
How the math works
Take a moneyline where Book A lists Yankees at +120 (implied 45.45%) and Book B lists Red Sox at +110 (implied 47.62%). Total implied: 93.07%. That's 6.93% below 100%, so betting both sides with the right stake split guarantees a ~6.93% return on your total bankroll.
To lock equal payouts, stake each side in proportion to 1/decimal-odds. For a $100 bankroll at +120/+110:
- Side A stake: $100 × (1/2.20) / (1/2.20 + 1/2.10) = ~$48.84
- Side B stake: $100 × (1/2.10) / (1/2.20 + 1/2.10) = ~$51.16
- Whichever side hits, payout ≈ $107.45 → locked $7.45 profit (7.45% return)
Why most published arbs are tiny (and why you should care anyway)
Sharp markets (Pinnacle, Circa) usually price within 1-2% of the true fair line. Arbs that show up in public tools are typically 0.5-3% — the edge is small, but it's risk-free (in theory). Volume is what turns thin arbs into real income. A 2% arb on $10,000 total stake earns $200 per placement; a half-dozen per day is not unusual.
The risks arbers actually worry about
Arb betting isn't actually risk-free in practice. Top risks, in rough order of frequency:
- Line movement. You place Side A, and before you can place Side B, the line moves and the arb closes. You're now exposed to a one-sided bet, not an arb.
- Book limits. Most retail books cap your stake on individual bets (often $50-$500 for retail, higher for sharper books). Kelly-large arb positions are often impossible.
- Stake limiting / account closure. Books detect arbers via betting patterns and limit stakes or close accounts. This is the biggest long-term arbing risk — your usable books shrink over time.
- Suspended / voided bets. If one book voids a bet (suspect market, player scratch, rule 4 adjustment) and the other settles normally, your arb collapses into a one-sided position.
- Key differences in book rules. Different settlement rules for overtime/extra innings/suspensions can turn an apparent arb into a net loss.
Why this tool shows a manual calculator, not a live scanner
Most public "arb finders" are paid tools (Oddsjam, Unabated, BetBurger) that subscribe to live multi-book odds feeds and push notifications within seconds of an arb appearing. Our model is different: we surface sim-derived +EV edges on MLB, not cross-book arbs. The Mongoose Bets data pipeline aggregates each market to a single best-price per side before the frontend sees it, which is perfect for +EV analysis but doesn't carry the per-book breakdown you need to detect arbs programmatically.
Use the manual calculator on this page when you spot a line discrepancy across your books. For real-time automated scanning across the US retail books, a paid tool is likely the right choice — see our Mongoose Bets vs Oddsjam comparison for a breakdown.
Frequently asked questions
- What is arbitrage betting?
- Arbitrage betting is placing bets on every outcome of a market across different sportsbooks so that you lock in a guaranteed profit regardless of which outcome wins. The math works when the sum of the best implied probabilities across books is less than 100%. The gap below 100% is your guaranteed return.
- Is arbitrage betting legal?
- In most US states with legal sports betting, arbing is legal — no law explicitly bans it. However, sportsbook terms of service often allow books to limit or close accounts suspected of arbing, and individual books may void winnings if they detect clear arb patterns. Consult your state's gambling laws and the specific book's terms before placing real arb bets.
- How much money can you make arbitrage betting?
- Most published arbs are 0.5-3% return. Serious arbers handle large volume at thin edges. Realistic returns for a part-time arber with $10,000-$50,000 in book bankrolls average 5-15% annualized on that capital — before accounting for the operational work of placing each bet and the steady pace of book accounts being limited.
- Why is my account getting limited after only a few bets?
- Retail sportsbooks profile bettors on deposit patterns, stake sizes, and market selection — not just on whether bets win or lose. Consistently beating the closing line, betting quickly after lines post, or sizing in the top 5% of retail stakes flags an account as "sharp" within the first few bets. Once flagged, stake limits drop to pennies. Sophisticated arbers spread activity across many accounts and blend in retail-looking bets to extend each account's useful lifespan.
For today's actual +EV MLB bets run through 2,500 Monte Carlo simulations, see Best Bets →