How to use it
- Choose the odds format you have: American, decimal, fractional or probability.
- Enter the odds and your stake.
- Read the payout, profit and the same odds in every other format.
- Switch to Bookmaker margin to calculate the vig on a whole market.
The three odds formats
- American (moneyline): used by US sportsbooks. +150 means a $100 bet wins $150 profit. −200 means you must bet $200 to win $100 profit. Plus means underdog, minus means favorite.
- Decimal: common in Europe, Canada and Australia. The number is the total return per $1 staked, including your stake: 2.50 returns $2.50 for every $1.
- Fractional: traditional in the UK. 3/2 means $3 profit for every $2 staked.
| American | Decimal | Fractional | Implied probability |
|---|---|---|---|
| −300 | 1.333 | 1/3 | 75.0% |
| −200 | 1.500 | 1/2 | 66.7% |
| −110 | 1.909 | 10/11 | 52.4% |
| +100 | 2.000 | 1/1 (evens) | 50.0% |
| +150 | 2.500 | 3/2 | 40.0% |
| +300 | 4.000 | 3/1 | 25.0% |
Conversion formulas
American to decimal:
- Positive: decimal = 1 + American ÷ 100 (+150 → 2.50)
- Negative: decimal = 1 + 100 ÷ |American| (−200 → 1.50)
Decimal to American: if decimal ≥ 2, American = (decimal − 1) × 100; otherwise American = −100 ÷ (decimal − 1).
Implied probability = 1 ÷ decimal odds (2.50 → 40%).
Payout = stake × decimal odds; profit = payout − stake. A $100 bet at +150 pays $250 in total, $150 of it profit.
Fractional odds that don't simplify neatly are approximated with the closest fraction with a denominator up to 100, marked "rounded" when it isn't exact.
Worked example: a single bet
You like an underdog at +180 and want to bet $50.
- Decimal odds: 1 + 180 ÷ 100 = 2.80
- Payout if it wins: $50 × 2.80 = $140
- Profit: $140 − $50 = $90
- Implied probability: 1 ÷ 2.80 = 35.7%
The same bet is 9/5 in fractional odds. If the other side of the game is priced at −220 (decimal 1.4545, implied 68.75%), the two sides add up to 104.5%, so the vig on that market is about 4.5%.
What the vig (margin) is
Add up the implied probabilities of every outcome in a market. In a fair market they would total exactly 100%. Sportsbooks build in a margin, so the total is higher; the excess is the overround, often called the vig or juice.
Example: both sides of an NFL spread at −110. Each implies 52.4%, so the total is 104.8% and the margin is 4.8%.
In Bookmaker margin mode, enter the decimal odds for every outcome (convert American odds first). The tool shows the margin and the no-vig (fair) probability and odds for each outcome, by scaling the implied probabilities so they add up to 100%. Comparing no-vig odds across sportsbooks is a common way to spot the best price.
Reading implied probability
Implied probability tells you how likely an outcome must be for the bet to break even at those odds. If you think a team wins 45% of the time and the odds imply 40% (+150), the price looks generous to you; if the odds imply 52% (−110), it doesn't. Your own estimate is the hard part, and the margin means the average bettor loses over time.
Bet responsibly
Sports betting is legal in many but not all US states, and the rules differ by state. Only bet money you can afford to lose and set limits before you start. If gambling is causing problems for you or someone you know, call or text 1-800-GAMBLER or visit the National Council on Problem Gambling at ncpgambling.org. This tool is for calculation only and is not betting advice.
Frequently asked questions
What does +150 mean in betting?
A $100 bet at +150 wins $150 profit, returning $250 in total. The implied probability is 40%.
What does −110 mean?
You bet $110 to win $100 profit. The implied probability is about 52.4%.
How do I convert American odds to decimal?
For positive odds, add 1 to the odds divided by 100. For negative odds, add 1 to 100 divided by the absolute value. +200 = 3.00; −250 = 1.40.
What is implied probability?
The chance of an outcome that the odds represent: 1 divided by the decimal odds. It includes the sportsbook's margin.
What is the vig?
The sportsbook's built-in margin: how much the implied probabilities of all outcomes exceed 100%. Two sides at −110 carry a vig of about 4.8%.
Last updated: November 12, 2026