Surebets United States: Arbitrage Math, Margins and Realistic Limits
A surebet (arbitrage) exists when the best available prices for every outcome of a market, taken across two or more sportsbooks, produce a combined implied probability below 100%. In that gap you can stake proportionally on each outcome and lock a return regardless of the result. The math is simple; the practical constraints in the US market are not. Sportsbooks here average roughly 4.2%–6.3% margin on the markets we sample, which means genuine arbitrage windows are thin, short-lived, and depend on catching a lagging price before it moves. This page explains the calculation, where the sharpest prices tend to sit based on our best-price data, and the account and line-movement limits that decide whether a surebet survives to settlement.
Lowest combined margins right now
What a surebet actually is
A surebet is a set of bets on all outcomes of a single event, placed at prices that guarantee a positive return no matter which outcome wins. It works because different sportsbooks price the same market differently. When two operators disagree enough — one posts a generous home price, another a generous away price — the two best numbers can add up to less than a fair 100% book.
Arbitrage betting, sure bets and surebets all describe the same mechanic. The edge comes entirely from price discrepancy between books, not from predicting the result. That is the appeal and also the ceiling: your profit is capped by how far the combined margin sits below 100%, and in a market where books cluster tightly, that gap is usually small.
How combined margin is computed from best prices
Convert each best price to implied probability, then sum them. In American odds, a +150 price implies 100 / (150 + 100) = 40.0%. A -130 price implies 130 / (130 + 100) = 56.5%.
Example two-way market: - Best Team A price: +120 → 45.45% implied - Best Team B price (different book): +115 → 46.51% implied - Combined book: 91.96%
Because the combined implied probability is below 100%, the market is an arbitrage. The margin against you is 91.96% − 100% = −8.04%, i.e. an 8.04% surebet in that example. Stakes are split so each outcome returns the same total: the share on each side is proportional to its implied probability divided by the combined book.
In practice, single-book margins do the opposite of this. Our sampled average margins sit around 4.25% (DraftKings, 1,068 markets), 4.46% (FanDuel, 596), 4.25% (Fanatics, 466), 5.21% (Caesars, 906), 5.27% (BetMGM, 438) and 6.35% (BetRivers, 480). A within-book market at +5% margin can never be an arbitrage on its own — the gap only appears when the best leg from one book meets the best opposing leg from another.
Where the sharpest prices sit
Best-price share tells you how often an operator posts the top number in a market — the raw material of any surebet. Across our sampled markets, DraftKings leads at 54.0% best-price share, ahead of Fanatics (41.8%), FanDuel (36.1%) and Caesars (36.2%). BetRivers (28.3%) and BetMGM (19.9%) top a market far less often, and BetMGM also carries the second-highest sampled margin (5.21%).
The practical read: a two-leg arbitrage most often pairs a leading best-price book (DraftKings, Fanatics, FanDuel) with a book that happens to lag on the opposite side of that specific market. bet365, DraftKings, FanDuel and BetMGM also score highest on market coverage (9.6, 9.0, 8.9, 8.7 on our scale), which matters because a surebet needs the same market listed at both books simultaneously. Note that best-price share and margin are separate metrics — a book can post the best number in one market while carrying a wider average margin overall.
Dropping odds and where windows open
Dropping odds arbitrage is the most common source of a live surebet. When one book shortens a price fast — steam on an NFL spread, a late scratch in the NBA, a line reacting to a UFC weigh-in — the opposite side at a slower book can briefly stay long enough to complete an arbitrage. The window is a function of how quickly each operator repositions.
This is why line-movement tracking matters more than any single price snapshot. Our market movers and betting odds pages show which way a number is trending; a surebet built on a stale leg disappears the moment the lagging book catches up, often in seconds for high-liquidity markets like MLB run lines or NBA totals.
Using an arbitrage calculator
An arbitrage calculator (or surebet finder) turns the margin math into stakes. The workflow:
- Enter the best price for each outcome, each from the book offering it.
- The calculator converts prices to implied probabilities and sums them. Below 100% = arbitrage.
- Enter your total stake. The tool splits it across outcomes so each returns the same amount.
- It outputs guaranteed return and the locked margin.
The finder's job is only to flag the discrepancy and size the stakes. It cannot guarantee both legs fill at the displayed prices — that is the execution risk, and it is where most theoretical surebets fail. Treat any calculator output as a plan that is valid only until the next price refresh. See our betting tools for related utilities.
Realistic limitations
Arbitrage in the US carries hard practical limits, and no calculator removes them:
- Price moves: the biggest risk. You place leg one, the second book moves before you fill leg two, and the surebet becomes a one-sided position. Fast markets close the gap in seconds.
- Stake limits: sportsbooks cap how much they accept on sharp markets, capping the profit on any single arbitrage.
- Account restrictions: operators actively monitor for arbitrage patterns. Sustained arb activity commonly leads to reduced limits or restricted accounts — books are under no obligation to keep offering you the price.
- Rounding and minimums: with $10 minimum deposits and stake minimums, small-margin arbs may not divide cleanly into whole stakes.
- Voids and rule differences: if one book voids a leg (e.g. differing dead-heat or postponement rules) the hedge breaks and you hold a naked position.
- State availability: US betting is regulated state by state. Two books needed for an arb must both be legal and live in your state, or the pairing does not exist for you.
We make no profit promise. A surebet is a mathematical structure, not a guaranteed income; the limitations above regularly turn a theoretical edge into a break-even or losing outcome.
Legality and state-by-state availability
US sports betting is regulated by state gaming regulators — NJ DGE, NYSGC, PGCB, MGCB and others — not by a single federal body. An operator licensed in New Jersey is not automatically legal in New York, Pennsylvania, Michigan, Colorado, Ohio, Illinois, Arizona, Virginia or Massachusetts. Minimum age is 21 at licensed US sportsbooks.
This directly affects arbitrage: your available book pairings are limited to operators live and licensed in your own state. A discrepancy between DraftKings and FanDuel is only actionable where both hold a licence and operate. Check our legal betting sites page and your state regulator before assuming a market pairing is available to you.
FAQ
What is a surebet?
A surebet, or arbitrage, is a group of bets covering every outcome of one event at prices — usually from different sportsbooks — whose combined implied probability is below 100%. Stakes are split so the total return is the same regardless of the result, locking a positive outcome. The edge comes from price differences between books, not from predicting the winner.
How do I know if odds form an arbitrage?
Convert each best price to implied probability and add them. For +120 (45.45%) and +115 (46.51%) the combined book is 91.96% — below 100%, so it is a surebet. Any total under 100% is an arbitrage; the further below, the larger the locked margin. An arbitrage calculator does this and sizes the stakes for you.
Which US sportsbook has the sharpest prices?
By best-price share in our samples, DraftKings posts the top number most often at 54.0%, followed by Fanatics (41.8%), Caesars (36.2%) and FanDuel (36.1%). By sampled margin, DraftKings and Fanatics (both ~4.25%) run tighter than BetMGM (5.21%) and BetRivers (6.35%). Surebets typically pair a leading best-price book with a book lagging on the opposite side of a specific market.
Can sportsbooks restrict me for arbitrage betting?
Yes. US operators monitor for arbitrage patterns and commonly respond with reduced stake limits or account restrictions. There is no obligation for a book to keep offering you a price. This, along with fast line moves and stake caps, is why arbitrage is not a guaranteed income stream.
Do dropping odds create surebets?
Often. When one book shortens a price quickly and a slower book leaves the opposite side long, a brief arbitrage window opens. These dropping-odds surebets are short-lived — high-liquidity markets can close the gap in seconds — so line-movement tracking matters more than a single snapshot.
Is arbitrage betting legal in the US?
Placing bets at licensed sportsbooks is legal where sports betting is regulated, but availability is state by state. Both books in an arbitrage must be licensed and live in your state, and the minimum age is 21. There is no federal sports-betting licence; NJ DGE, NYSGC, PGCB and other state regulators set the rules where you are.