WOYALE.
Odds are three ways of writing the same price. American odds dominate US sportsbooks, decimal odds are common on exchanges and in crypto sites, and fractional odds appear in horse racing and UK betting. Every format converts to an implied probability, which shows what a price actually says.
American odds
American (moneyline) odds use a plus or minus sign and a number built around $100.
- Plus odds (+150): a $100 stake wins $150 profit. The number is the profit on $100. Plus odds are for the underdog.
- Minus odds (-200): you must stake $200 to win $100 profit. The number is the stake needed to win $100. Minus odds are for the favorite.
Even money is +100 (sometimes written EVEN).
Decimal odds
Decimal odds show the total return for each $1 staked, stake included.
- 2.50: $1 returns $2.50, so profit is $1.50.
- 1.50: $1 returns $1.50, so profit is $0.50.
- 2.00: even money.
To find profit, subtract 1 from the decimal figure. Pari-mutuel payouts are decimal by nature: a pool paying $2.25 per $1 is 2.25. See how pools work.
Fractional odds
Fractional odds show profit relative to stake.
- 3/2 (said “three-to-two”): win $3 for every $2 staked.
- 1/2: win $1 for every $2 staked.
- 4/1: win $4 for every $1.
- 1/1: even money.
Horse racing in the US often shows odds like 5-2 or 9-5, which read the same way.
Converting between them
American to decimal
- Positive (+X): decimal = 1 + X/100. For +150: 1 + 1.50 = 2.50.
- Negative (-X): decimal = 1 + 100/X. For -200: 1 + 0.50 = 1.50.
Decimal to American
- Decimal 2.00 or higher: American = (decimal − 1) × 100. For 2.50: +150.
- Decimal under 2.00: American = −100 ÷ (decimal − 1). For 1.50: −100 ÷ 0.50 = -200.
Fractional to decimal
Decimal = 1 + (top ÷ bottom). For 3/2: 1 + 1.5 = 2.50.
Reference table
| American | Decimal | Fractional | Implied probability |
|---|---|---|---|
| -200 | 1.50 | 1/2 | 66.67% |
| -110 | 1.909 | 10/11 | 52.38% |
| +100 | 2.00 | 1/1 | 50.00% |
| +150 | 2.50 | 3/2 | 40.00% |
| +400 | 5.00 | 4/1 | 20.00% |
Implied probability
Implied probability is the chance of winning that makes a price break even. It is the number to compare against your own view of a game.
- Decimal: probability = 1 ÷ decimal. For 2.50: 1 ÷ 2.50 = 40%.
- Positive American (+X): probability = 100 ÷ (X + 100). For +150: 100 ÷ 250 = 40%.
- Negative American (-X): probability = X ÷ (X + 100). For -110: 110 ÷ 210 = 52.38%.
- Fractional (a/b): probability = b ÷ (a + b). For 3/2: 2 ÷ 5 = 40%.
If you think a +150 team wins more than 40% of the time, the price offers value by your own estimate. If you think less, it does not.
Why a two-way market adds to more than 100%
A fair coin-flip market would price each side at +100 and each side would imply 50%, totaling 100%. Sportsbooks do not do that. A typical game might be -110 on both sides: 52.38% + 52.38% = 104.76%. The extra 4.76 points is the vig, the margin the book builds in.
The true chances of the two outcomes must add to 100%. So the quoted prices overstate each side’s probability. To get a fairer read, you remove the vig.
Removing the vig: a worked example
A game is priced like this:
- Team A: -115
- Team B: -105
Step 1: implied probabilities
- Team A: 115 ÷ 215 = 53.49%
- Team B: 105 ÷ 205 = 51.22%
- Total: 104.71%
Step 2: divide each by the total (this method scales both down in proportion)
- Team A: 53.49 ÷ 104.71 = 51.08%
- Team B: 51.22 ÷ 104.71 = 48.92%
These now add to 100%. The vig took about 2.3 to 2.4 points off each side’s implied probability.
Step 3: back to odds, if you want them
- Team A fair decimal: 1 ÷ 0.5108 = 1.958, about -104.
- Team B fair decimal: 1 ÷ 0.4892 = 2.044, about +104.
The book offers -115 where the vig-free price is about -104. Team B at -105 compares with a fair +104, so it costs you very little, while Team A costs more.
A note on method
Dividing by the total is the simplest method. It is not the only one, and it assumes the vig is spread evenly in proportion to probability. Favorites and longshots often carry the margin unevenly, so treat the result as an estimate. There are other methods, such as the power or additive approaches, that give slightly different answers on lopsided markets.
Odds in pools and on crypto sites
Pools show decimal-style payouts, because the math is a return per dollar. US horse racing pools are pari-mutuel and regulated state by state, as with the California Horse Racing Board. Many crypto sites let you switch format in settings. Always check which format is active before you read a price. A 2.00 in decimal is even money, but in fractional it would mean 2/1, a very different price.
Your odds only tell you the price. Whether the site is licensed or pays out is a separate question: offshore crypto sportsbooks are not licensed in any US state. See are offshore sportsbooks legal.
Common questions
Which odds format is best?
Decimal is the easiest for comparing and for maths, because it shows total return directly. American is what most US books display, so you will need to read it either way.
What does a minus sign mean in American odds?
The favorite. A minus number is the amount you must stake to win $100. Larger minus numbers mean heavier favorites.
Do implied probabilities include the vig?
Yes. The raw implied probabilities of both sides add to more than 100%. Removing the vig scales them to 100%, which gives a closer estimate of the market’s true view.