KEY TAKEAWAYS
Odds are the language of every betting market, and they come in several formats that describe the same idea in different ways. This glossary defines 24 betting odds terms, from American, decimal and fractional formats to implied probability, overround, favorites and underdogs, and the vocabulary of line movement. Each entry gives a plain definition, an example of the term in use and a worked figure where one helps. The terms are grouped into four themes: odds formats, probability and margin, favorites, underdogs and payouts, and lines and line movement. A quick-reference table near the end sums up every entry in one line, and the figures follow the standard conversions, so -110 becomes 1.909 in decimal and an implied probability of 52.38%. The definitions describe the vocabulary of odds only, and they do not suggest which bets to place.
Odds Formats
Odds are written in a few standard formats, and the same price can look very different in each one. These terms name the formats and the common price labels.
American odds
Definition: A format that shows either how much must be risked to win $100 (a minus number) or how much $100 wins (a plus number).
Example: “The game was listed at -150 and +130 in American odds.”
Also called moneyline odds. A -150 price risks $150 to win $100, and +150 wins $150 on a $100 bet. Converted to decimal, -150 is 1.667 and +150 is 2.50.
Decimal odds
Definition: A format that shows the total return for each 1 unit staked, including the stake itself.
Example: “At decimal odds of 2.50, a $10 stake returns $25.”
Subtract 1 to get the profit per unit, so 2.50 gives $15 of profit on $10.
Fractional odds
Definition: A format that shows the profit relative to the stake as a fraction, such as 5/2.
Example: “The horse was 5/2, so a $2 stake would win $5.”
5/2 equals 3.50 in decimal odds and an implied probability of 28.57%.
Even money
Definition: A price at which the profit equals the stake, written +100 in American odds, 2.00 in decimal and 1/1 in fractional.
Example: “It was an even-money bet: risk $50 to win $50.”
An even-money price implies a 50% chance before any margin is added.
Odds-on
Definition: A price that is shorter than even money, so the bettor must risk more than they can win.
Example: “At 1/2, the favorite was odds-on.”
1/2 is 1.50 in decimal and implies a probability of about 66.67%.
Odds against
Definition: A price that is longer than even money, or the ratio of an event not happening to it happening.
Example: “The odds were 4/1 against, which is 5.00 in decimal.”
Odds of 4 to 1 against imply a probability of 1 ÷ 5.00 = 20%.
Probability and Margin
Odds can be turned into probabilities, and the gap between the two reveals the margin built into a price. These terms cover that vocabulary.
Probability
Definition: A number from 0 to 1, or 0% to 100%, that describes how likely an event is.
Example: “A fair coin has a probability of 50% of landing heads.”
With two dice there are 36 combinations, so the probability of rolling a 7 is 6/36, about 16.67%.
Implied probability
Definition: The chance of an outcome that a set of odds represents, found by dividing 1 by the decimal odds.
Example: “A price of -110 has an implied probability of 52.38%.”
-110 is 1.909 in decimal, so 1 ÷ 1.909 ≈ 52.38%. A price of +200 is 3.00, which implies 33.33%.
Fair odds
Definition: Odds that match the true probability of an outcome, with no margin added.
Example: “A coin flip at fair odds would pay +100, or 2.00.”
Also called true odds. They are a theoretical benchmark, since the real probability is rarely known for certain.
Overround
Definition: The amount by which the implied probabilities of all outcomes in a market add up to more than 100%.
Example: “Both sides at -110 gave an overround of 104.76%.”
The calculation is 52.38% + 52.38% = 104.76%. The extra 4.76% is the margin built into the prices.
No-vig odds
Definition: Odds after the margin has been removed, so that the implied probabilities add up to exactly 100%.
Example: “Dividing each 52.38% by 104.76% gave no-vig odds of 50% for each side.”
Also called no-juice or devigged odds. The result is an estimate of the market’s view, not a guarantee of the true chance.
Vig
Definition: The margin a sportsbook builds into its prices, which means a bettor must risk more than the win amount on a balanced market.
Example: “At -110 on both sides, the vig means risking $110 to win $100.”
Short for vigorish, also called juice. Prices of -110 on both sides are common for evenly matched two-way markets.
Favorites, Underdogs and Payouts
These terms describe which side the market favors and how much a winning bet returns.
Favorite
Definition: The side with the highest implied probability in a market, shown by a minus price or decimal odds below 2.00 in a two-way market.
Example: “The favorite was -200, so a $200 bet would win $100.”
-200 is 1.50 in decimal and implies a probability of 66.67%.
Underdog
Definition: The side with the lowest implied probability in a market, shown by a plus price or decimal odds above 2.00 in a two-way market.
Example: “The underdog was +200, so a $100 bet would win $200.”
Often shortened to dog. +200 is 3.00 in decimal and implies 33.33%.
Longshot
Definition: An outcome with very long odds, which the market considers very unlikely.
Example: “A 50/1 longshot won the race.”
At 50/1 the decimal price is 51.00, and the implied probability is 1 ÷ 51 ≈ 1.96%.
Chalk
Definition: Informal slang for the favorite, or for a result that goes the way the favorites were expected to.
Example: “The chalk won most of the games on Saturday.”
Informal register, used in casual betting talk.
Payout
Definition: The amount a winning bet returns, which in many venues includes the original stake.
Example: “The payout on a $10 bet at 2.50 was $25.”
Some places use payout to mean profit only, so the meaning depends on the venue.
Profit
Definition: The amount won on a bet, not counting the stake that is returned.
Example: “A $10 bet at 2.50 returned $25, which was $15 of profit.”
Profit equals total return minus the stake. A losing bet has no profit and loses the stake.
Lines and Line Movement
Odds change between the moment a market opens and the start of an event. The terms below describe those changes.
Line
Definition: The odds, spread or total that a sportsbook posts for a market, often used as a general word for the current price.
Example: “The line on the game changed twice on Friday.”
Also called the price or number. In U.S. betting, line often means the spread or total.
Opening line
Definition: The first line a sportsbook posts for a market.
Example: “The opening line was 3.5 points and later moved to 4.”
Different sportsbooks can post different opening lines for the same market.
Closing line
Definition: The last line available before an event starts.
Example: “The closing line was -120, up from -110 at the open.”
It is often used as a reference point for how a price changed over time.
Line movement
Definition: A change in the odds, spread or total for a market after it opens.
Example: “The line movement shifted the favorite from -3 to -4.”
Movement can reflect betting activity, injury news or other new information.
Sharp money
Definition: Informal term for bets placed by bettors whom sportsbooks consider skilled, which can influence line movement.
Example: “The line moved quickly, and some described it as sharp money.”
Which bettors count as sharp is decided by each sportsbook, and the label is not an official measure.
Reverse line movement
Definition: A line move in the opposite direction of where most of the bets are placed.
Example: “Most bets were on the favorite, yet the line moved toward the underdog.”
It is described by comparing the share of bets with the direction of the line, and the data comes from public betting percentages.
Quick-Reference Table
| Term | Short definition |
|---|---|
| American odds | Plus and minus format |
| Decimal odds | Total return per unit staked |
| Fractional odds | Profit over stake as a fraction |
| Even money | Profit equals stake |
| Odds-on | Shorter than even money |
| Odds against | Longer than even money |
| Probability | Chance from 0 to 100% |
| Implied probability | Probability built into the price |
| Fair odds | Odds with no margin |
| Overround | Probabilities above 100% |
| No-vig odds | Odds with the margin removed |
| Vig | Margin built into the price |
| Favorite | Side the market expects to win |
| Underdog | Side the market expects to lose |
| Longshot | Very long odds |
| Chalk | Slang for favorite |
| Payout | Amount a winning bet returns |
| Profit | Winnings beyond the stake |
| Line | Posted odds or number |
| Opening line | First posted price |
| Closing line | Last price before the start |
| Line movement | Change in the line |
| Sharp money | Bets from skilled bettors |
| Reverse line movement | Line moves against the crowd |
Related Glossaries
Odds vocabulary connects to the wider language of betting. Terms such as vig, hold and house edge are covered in the gambling money terms glossary, and the bets that odds are attached to are defined in the types of sports bets glossary. The entries above focus on how prices and probabilities are written and read.
