Sure Betting Glossary: Terms Every Arbitrage Bettor Should Know
Implied probability, closing line value, book percentage, scalping. A quick reference for the vocabulary that shows up across arbitrage betting content, in one place.
What does 'implied probability' mean in sure betting?
Implied probability is the chance of an outcome that a bookmaker's decimal odds represent mathematically, calculated as 1 divided by the decimal odds. It's the core building block behind every arbitrage calculation: if the implied probabilities of all outcomes across bookmakers add up to less than 100%, a sure bet exists.
Core Pricing Terms
Implied probability: the probability a given decimal odds figure represents, calculated as 1 divided by the odds. A 2.00 odds implies a 50% probability.
Book percentage (overround): the sum of implied probabilities across all outcomes in a market. A book percentage above 100% is a bookmaker's built-in margin; below 100% across combined bookmakers is an arbitrage opportunity, covered in detail in our calculator formulas guide.
Margin: the guaranteed profit percentage on a sure bet, calculated from how far below 100% the combined implied probability sits.
Execution and Risk Terms
Legging (or scalping): placing one side of an arbitrage position and being unable to complete the other side before the price moves, leaving an unhedged, uncovered bet on a single outcome instead of a locked-in profit.
Hedging: placing a bet specifically to offset risk on an existing position, the general concept that arbitrage betting applies systematically across every outcome at once.
Slippage: the difference between the price you expected and the price you actually got when placing a bet, more relevant on exchanges and prediction markets than fixed-odds bookmakers, covered in our guide on betting exchange arbitrage.
Market Structure Terms
Closing line value (CLV): how favorable your bet's odds were compared to the final odds available right before the event started. Consistently positive CLV is one of the more reliable indicators of genuinely sharp betting, distinct from arbitrage's guaranteed-outcome approach.
Two-way / three-way market: a market with two possible outcomes (like a tennis match) or three (like football's home/draw/away). The stake-splitting formula differs between them, explained in our calculator guide.
Moneyline, spread, and totals: the three most common market types across most sports, covered in full in our betting markets guide.
Account and Business Terms
Limiting (or gubbing): a bookmaker restricting a customer's maximum stake size, usually well before any full account closure, discussed in detail in our guide on why bookmakers reduce stakes after you win.
KYC (Know Your Customer): the identity verification process most licensed bookmakers require before approving withdrawals, typically completed once per account shortly after signup.
Strategy Terms
Value betting: placing a single bet judged to be priced better than its true probability, a different strategy from arbitrage betting that carries more variance since only one outcome is backed, covered in our guide on arbitrage vs value betting.
Back and lay: on a betting exchange, backing means betting for an outcome, laying means betting against it, acting as the bookmaker for that specific position. Both terms come up together in back-lay arbitrage strategies.
Frequently asked
What's the difference between implied probability and book percentage?
Implied probability applies to a single odds figure for one outcome. Book percentage is the sum of implied probabilities across all outcomes in a market, which tells you whether a bookmaker's overall pricing includes a margin or, combined across bookmakers, an arbitrage opportunity.
What does it mean to get 'legged' on a sure bet?
It means one side of your arbitrage position got placed but the other didn't, usually because odds moved before you could complete it, leaving you with a single unhedged bet instead of a guaranteed profit.
Is closing line value the same thing as an arbitrage margin?
No. Closing line value measures how good your odds were relative to the final market price on a single bet, while arbitrage margin is the guaranteed profit percentage from combining odds across multiple bookmakers on every outcome.
Why do bookmakers use the term 'gubbed' for account limits?
It's informal betting community slang for having your maximum stake significantly reduced or your account restricted, distinct from a full account closure.
Do these terms apply the same way to prediction markets and exchanges?
Most of the pricing terms (implied probability, margin) apply directly. Execution-specific terms like slippage are more relevant to exchanges and prediction markets than fixed-odds bookmakers, covered in our guide on <a href="/blog/prediction-market-arbitrage-vs-sports-betting-arbitrage">prediction market vs sportsbook arbitrage</a>.