Expected value is the average result of a bet if it were repeated many times, weighting each possible payout by its probability. A positive expected value suggests a bet is profitable over the long run, while a negative value indicates an expected loss. It underpins disciplined, probability-based betting decisions.
The betting margin is the commission a bookmaker builds into its odds, ensuring the implied probabilities of a market exceed 100%. It represents the operator's theoretical profit and the cost a bettor pays to place a wager. Lower margins give bettors better long-term value, and margins vary widely between operators and markets.
Overround is the amount by which the implied probabilities of all outcomes in a betting market exceed 100%. It quantifies the bookmaker's built-in margin on that market. An overround of 107%, for example, means bettors are collectively paying a premium relative to a theoretically fair, margin-free market.
Arbitrage betting involves placing bets on all possible outcomes of an event across different operators, exploiting price differences to lock in a profit regardless of the result. It relies on finding combined odds whose implied probabilities sum to less than 100%. Opportunities are small, short-lived and may breach operator terms.
Closing line value measures how a bettor's odds compare with the final odds available just before an event starts. Consistently securing prices better than the closing line is widely regarded as a strong indicator of long-term betting skill, because the closing line tends to be an efficient estimate of true probabilities.
Hold percentage is the share of total amount wagered that a betting operator keeps as revenue after paying out winnings. Unlike the theoretical margin, actual hold reflects real betting patterns and results over a period. It is a key measure of an operator's profitability and typically differs from the built-in margin.
Variance describes how much actual betting or gambling results deviate from their expected average over time. High variance means larger swings in bankroll, both up and down, even when the underlying edge is unchanged. Understanding variance helps players set realistic expectations and avoid mistaking short-term luck for long-term skill.
Bankroll management is the practice of controlling how much of a dedicated gambling fund is risked on any single bet or session. By sizing stakes relative to the total bankroll, players aim to survive inevitable losing streaks and avoid ruin. It is a risk-control discipline, not a method of guaranteeing profit.
Positive EV betting is a strategy of placing only wagers whose expected value is greater than zero, meaning they are projected to profit over the long run. It requires estimating true probabilities more accurately than the odds imply, after accounting for the operator's margin. Short-term results still vary widely despite a genuine edge.
Implied probability is the likelihood of an outcome as expressed by its betting odds, converted into a percentage or decimal fraction. It reflects how often an event must occur for a stake to break even, before any bookmaker margin is removed. Comparing implied probability with your own estimate is central to identifying value.