NBA
MLB01 · The premise
What an arb is
An arbitrage is a pair of bets on opposite sides of the same market, placed at two different books, where the combined prices guarantee a profit regardless of the result. It exists only because two books briefly disagree on a number — one is slow to move, or aggressive to attract action — and you bridge the gap before they reconcile.
The test is simple: convert both prices to implied probability and add them. If the sum is under 100%, the market is paying out more than the full event is worth, and the difference is your locked margin. If the sum is 100% or more — which is nearly always, because of the vig — there is no arb.
02 · The arithmetic
The math
The arb condition, in implied probabilities:
Start with the case everyone misreads as an arb but isn’t. A total of 45.5 priced Over -110 at one book and Under -110 at another: each side implies 52.38%, summing to 104.76%. That’s the standard two-way hold — no arb, you’d lose the vig.
Worked example · A real arb
Now suppose Book 1 posts the Over at +105 while Book 2 still has the Under at -102. Stake $1,000 total.
Whichever side hits, you collect $1,007.30 on $1,000 risked. A locked +0.73% — and that is a good cross-book arb. The thinness is the point.
03 · Try it
Stake calculator
Enter two opposite-side prices and a bankroll. It tests for an arb, splits the stake for an equal payout, and shows the guaranteed profit and ROI.
Live · Arbitrage stake splitter
Stakes are split so the payout is identical whichever side wins. Profit assumes both legs fill at the prices shown — the entire premise of the next section.
04 · The hard part
Execution barriers
The math is the easy 5%. The other 95% is whether you can actually place both legs at the prices you saw — and keep your accounts open long enough to do it again.
Speed
The window is seconds to a couple of minutes. Place the second leg too slow and the line you needed is already gone.
Limits
Books cap how much you can stake on a soft market — often a few hundred dollars on a prop — so the dollar profit on a 0.5% arb is small by design.
Account closure
Books track who hits their mistakes. Repeat arbers get limited to pennies or closed outright; the access erodes faster than the bankroll grows.
Repricing mid-execution
Both sides can move while you're clicking. A leg that shifts turns a locked pair into a one-sided naked bet.
State availability
Cross-book arbing needs funded accounts at multiple legal operators in your jurisdiction — and not every book offers every market.
Withdrawal friction
Capital is tied up across several books. Pulling profit out and rebalancing between operators is its own slow, frictioned chore.
05 · Where they come from
When arbs appear
Arbs are a symptom of markets repricing at different speeds. They cluster around the same events that move lines hard:
- Injury & lineup news. A late scratch sends one book scrambling while another lags a beat behind.
- Weather flips. Wind and rain reprice totals in outdoor sports — unevenly, book to book.
- Steam that hasn't landed. A sharp move sweeps the market in seconds; for a moment, the slow books are off.
- New operators. A book in customer-acquisition mode posts aggressive lines that don't line up with the field.
Every one of those is also a sharp-money trigger — which is why a live cross-book scanner is the only practical way to catch arbs before they close.
06 · The honest read
Risk management
Treat arbitrage as a market-timing exercise, not an income stream. The structural ceiling on cross-book arbs is roughly 0.3% to 0.8% per cycle, the windows close in seconds, and the books that misprice will limit or close you for hitting them. The bettors who profit from arbing for any length of time treat it as a way to learn line shopping and bankroll discipline — and they size small, rotate books, and accept that the access is the constraint, not the math.
If you want a higher-variance cousin with a real upside, look at middles — overlapping lines where both sides can cash if the result lands in the gap. And whatever you bet, the return only compounds if you size it correctly; that’s the Kelly staking discipline.
Reference
Frequently asked
Can I live off arbitrage betting?
No — the returns are too thin and the access too fragile to treat arbing as income. Cross-book arbs typically clear 0.3% to 0.8% per cycle and vanish in seconds, and the books that price them wrong will limit or close any account that keeps hitting them. It works as a market-timing exercise and a way to learn line shopping, not as a paycheck.
Is arbitrage betting legal?
Arbitrage is legal in regulated betting markets — you're placing ordinary wagers at posted prices — but it almost always violates a sportsbook's terms of service. Books reserve the right to void bets, cap limits, or close accounts of bettors who systematically exploit pricing errors, so the real risk is commercial, not criminal.
How fast do I need to be?
An arbitrage window usually lives for seconds to a couple of minutes before one book corrects its price. Manual arbing means racing to place the second leg before the line moves, and automated systems do it in well under a second — which is why a slow second click can turn a locked profit into a one-sided position you didn't want.
What happens if one leg fills and the other doesn't?
If the second leg moves before you place it, you're left holding a single naked bet instead of a locked pair — exactly the directional risk arbitrage is supposed to eliminate. The disciplined response is to accept the one-sided position at its true value or hedge at whatever price is now available, and to size arbs small enough that a busted leg is survivable.
When do arbitrage opportunities actually appear?
Arbs surface when two books disagree on a price for a moment — most often after an injury or weather move, during a steam move that hasn't reached every book, or when a new operator posts aggressive lines to acquire customers. They're a symptom of markets repricing at different speeds, which is also why they close the instant the slower book catches up.
What's the difference between arbitrage and a middle?
Arbitrage locks a small guaranteed profit on opposite sides of the same line, while a middle bets two overlapping lines so both can cash if the result lands in the gap between them. An arb pays the same regardless of outcome; a middle accepts a tiny known cost (or a near-break-even hold) for a shot at a much larger payout when the number falls in the window.
Continue reading
The arbitrage example is re-derivable arithmetic, not a recorded play. Research and methodology only — Dynatyze is not a sportsbook and takes no wagers. Bet legally and within your means.