Guide · Reference

Arbitrage betting glossary

Every term you'll meet in arbitrage betting, on betting exchanges and on prediction markets like Kalshi and Polymarket, explained in plain English, with the numbers where they help.

Updated October 18, 2026 · 62 terms

A

Accumulator also: parlay, acca

A single bet that combines several selections; every one must win for the bet to pay. The odds multiply, which makes accumulators popular with casual bettors and rarely useful for arbitrage. See also: Parlay, hedge bet calculator

American odds also: moneyline odds

The US format. A plus sign shows the profit on a $100 stake (+150 wins $150); a minus sign shows the stake needed to win $100 (−120 means stake $120 to win $100). Convert them with the odds converter

Arbitrage also: arb, sure bet, surebet

Betting every outcome of an event at different sportsbooks, exchanges or prediction markets, at prices whose implied probabilities add up to less than 100%. Once every leg is accepted, the result is a profit whichever outcome wins. Check one with the arbitrage calculator

Arber

Someone who places arbitrage bets. Sportsbooks use the word, too, usually just before they limit an account.

B

Back bet

A bet that an outcome will happen. Every bet at a sportsbook is a back bet; on a betting exchange you can also lay.

Bankroll

The money set aside for betting, usually spread across several accounts so you never wait for a deposit when an opportunity appears.

Bet slip

Where you enter the stake and confirm a bet. Arbers fill in every slip before confirming any of them, to place both legs as fast as possible.

Bonus abuse

The term sportsbooks use in their terms for using a bonus in ways they don't allow, often including arbitrage. It can lead to the bonus and its winnings being cancelled. Read the bonus terms before you deposit.

Break-even

A trade that returns exactly what you staked on every outcome: no profit, no loss. Our calculators flag it, because any fee or odds move turns it into a loss.

C

Closing line value also: CLV

How the price you took compares with the final price before the event starts. Consistently beating the closing line is a sign you are finding real value, and a sign sportsbooks watch for.

Commission

What a betting exchange charges on your net winnings in a market, typically 2% to 5%. It lowers your effective odds, so always include it in the math. See also: Effective odds, UK exchange commission compared

Contract

On a prediction market, a yes-or-no position that pays $1 if its outcome happens and nothing if it doesn't. Its price in cents is the market's probability. See also: Prediction market

D

Decimal odds

The total return for each $1 staked, including the stake. 2.50 returns $2.50 for $1: $1.50 profit plus your dollar. The format used in Europe, Canada, Australia and on exchanges.

Draw no bet also: DNB

A soccer market where your stake is refunded if the match is drawn. It turns a three-way match into a two-way market.

E

Effective odds

The odds you really get after fees. On an exchange: 1 + (odds − 1) × (1 − commission), so 2.20 at 5% commission is really 2.14. On Kalshi: 1 / (price + fee per contract).

Expected value also: EV, +EV

The average result of a bet if you could place it many times. A positive-EV (+EV) bet is priced better than its true probability; any single one can lose, but over many bets the edge adds up. See also: Value bet

Betting exchange

A market where bettors bet against each other, with the exchange taking a commission instead of setting the odds. Betfair, Smarkets, Matchbook and Betdaq are the main ones. Exchanges don't limit winners. Exchanges in the UK

F

Fair odds

The odds with the sportsbook's margin removed, so the outcomes' implied probabilities add up to exactly 100%. Find them with the margin tool in the odds converter

Fractional odds

The UK and Irish format: profit over stake. 5/2 wins $5 for every $2 staked. Evens is 1/1.

Free bet

A bet credit from a sportsbook. When it wins you get the winnings but not the stake, so it is worth less than its face value; laying it at an exchange locks in typically 70% to 80% of it at higher odds. Use the free bet mode of the Back & Lay calculator

G

Gubbing

UK slang for a sportsbook restricting a customer: cutting maximum stakes, excluding the account from promotions, or closing it. It happens to accounts that win consistently or only take the best prices. How to arbitrage bet without getting limited

H

Handle

The total amount wagered at a sportsbook or in a market. Often quoted for US sportsbooks.

Hedge

A bet on the opposite side of one you already hold, placed later to lock in a profit or cut a loss. Arbitrage uses the same math, but places both bets at once. Hedge bet calculator

I

Implied probability

The chance a price suggests: 1 divided by the decimal odds. 2.50 implies 40%. Add up the best implied probabilities of every outcome: under 100% is an arbitrage.

In-play also: live betting

Betting while the event is under way. Live arbs are bigger and more frequent, but last seconds and get accounts limited faster than pre-match arbs.

K

Kalshi

A US prediction market regulated by the CFTC, where you trade yes-or-no contracts on sports and other events against other users. For US arbers it plays the role a betting exchange plays elsewhere. Kalshi arbitrage guide, Kalshi fees

KYC

"Know your customer": the identity checks a sportsbook or platform runs before you can withdraw. Complete it early, not when you urgently need your money.

L

Lay bet

A bet that an outcome will not happen, available on betting exchanges. You take the sportsbook's role: you win the other bettor's stake if the outcome doesn't happen, and pay their winnings if it does. Back & Lay calculator

Leg

One of the bets in an arbitrage or a parlay. A two-way arb has two legs. A "broken leg" is one that fails or is voided, leaving the other side uncovered.

Liability

What you stand to lose on a lay bet: lay stake × (lay odds − 1). The exchange holds it in your account until the market settles.

Limits also: restricted account

Maximum stakes a sportsbook sets for an account. For winning accounts they can drop to a few dollars. See also: Gubbing, Stake factoring

Liquidity

How much money is available to match at a given price on an exchange or prediction market. The best price may only be available for a small amount, so check depth before you size a trade.

M

Maker

On an exchange or prediction market, someone whose order rests on the book until someone else takes it. Makers often pay lower fees (nothing on Polymarket and on most Kalshi series), but a resting order may never fill. See also: Taker

Margin

Two meanings. A bookmaker margin is how far a book's implied probabilities add up above 100%, its built-in edge (a −110/−110 market carries about 4.8%). An arbitrage margin is how far below 100% the best prices add up, which is roughly your profit as a share of the money staked; typically 2% to 5%.

Matched betting

Using sportsbook bonuses and free bets, covered with a lay bet at an exchange, to extract their value with little risk. Popular in the UK; it overlaps with arbitrage.

Middle

Two bets on opposite sides of a line at different books, such as over 210.5 points at one and under 213.5 at another. Most results return about your stake; a result in between wins both bets.

Moneyline

A bet on who wins the game, with no point spread. Also the US name for American odds.

O

Order book

The list of orders waiting to be matched on an exchange or prediction market, at each price. Its depth shows how much you can trade before the price gets worse.

Overround also: vig, juice, the hold

The amount by which a sportsbook's implied probabilities add up to more than 100%: its hidden fee on every bet. Arbitrage beats it by taking each outcome from a different book.

P

Palpable error also: palp, obvious error

A price so clearly wrong that the sportsbook's terms let it void bets placed at it. Arbs built on obvious errors are risky: one leg can be voided after the other is placed.

Parlay

The US name for an accumulator. Parlays are often hedged on the last leg. Hedge bet calculator

Polymarket

A prediction market with an international platform that runs on a dollar-pegged digital currency and a separate CFTC-regulated US app. On a buy, it takes its fee in shares. Kalshi vs Polymarket

Pre-match

Betting before an event starts. Prices move more slowly, so it is where most arbers start.

Prediction market

An exchange for yes-or-no contracts on future events, such as Kalshi or Polymarket. You trade against other users and the platform charges a fee, so it has no reason to limit winners. Prediction market arbitrage

Push

A result that lands exactly on the line, so the bet is refunded. A whole-number line such as −3 can push; a half-point line such as −3.5 can't.

Q

Qualifying bet

A bet you must place to unlock a sportsbook bonus. Covered with a lay bet, it usually costs a small, fixed amount: the "qualifying loss".

R

Rounding stake rounding

Changing exact stakes such as $494.27 to round ones such as $495, so bets look normal to sportsbooks. It shifts the payouts slightly; the arbitrage calculator shows what it costs.

S

Scanner also: arb finder, odds scanner

Software that watches prices across many sportsbooks, exchanges and prediction markets and flags arbs and value bets as they appear. Best arbitrage betting software

Settlement rules

How a market decides the winner: the data source, the deadline, and what happens in overtime, a postponement or a draw. Both legs of an arb must settle by the same rules, or you hold two separate bets.

Sharp bookmaker

A sportsbook that makes money from volume and a low margin and accepts winning customers, such as Pinnacle. Its prices are close to the true probability, so it suits the second leg of an arb.

Soft bookmaker

A consumer sportsbook with a big market menu that updates prices more slowly, so most arb opportunities appear there. Soft books are also the quickest to limit arbers.

Stake

The amount you bet. In arbitrage, the stakes on each outcome are sized so every outcome pays the same.

Stake factoring

A sportsbook quietly reducing the maximum stake it will accept from an account, sometimes to pennies. The usual first step of gubbing.

Sure bet

Another name for an arbitrage. The "sure" refers to the math once every leg is accepted, not to any single bet.

T

Taker

Someone whose order fills immediately against an order already on the book. Takers pay the standard fee: on Kalshi, 0.07 × contracts × price × (1 − price) on most sports. Kalshi fees explained

Three-way market

A market with three outcomes, such as home, draw and away in soccer. An arb needs a bet on each, or one back bet plus a lay bet at an exchange.

Two-way market

A market with two outcomes, such as a tennis match or an NBA game winner. The simplest kind of arb.

V

Value bet

A single bet at odds higher than the outcome's true probability, usually judged against sharp books. Unlike an arb it can lose, but over many bets the edge adds up. Several scanners find both. See also: Expected value

Vig also: vigorish, juice

The sportsbook's built-in margin. See Overround

Void bet

A bet cancelled by the sportsbook, with the stake returned. Usually caused by an obvious price error or a cancelled event. In an arb, a voided leg leaves the other uncovered.

W

Wagering requirement also: playthrough, rollover

How much you must bet before you can withdraw a bonus, for example 3× the bonus at minimum odds of 1.80 within 30 days. Check what it is calculated on, the minimum odds, the deadline and excluded markets.

Y

YES / NO shares

The two sides of a prediction market contract. Exactly one pays $1, so buying YES on one platform and NO on another for less than $1 combined, after fees, is an arbitrage. Kalshi arbitrage calculator