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Betting odds do three jobs at once. They tell you which side the sportsbook thinks is more likely to win, what your payout looks like if you're right, and what implied probability the price assumes. Every sportsbook in the world expresses the same underlying number in one of three formats: American odds (used in US sportsbooks), decimal odds (used in Europe, Canada, and Australia), and fractional odds (used in the UK and on horse racing tracks worldwide).
This guide covers how each format works, the conversion math between them, how to translate any price into an implied probability, and where each format shows up. Most US bettors only need American odds. Fluency in all three is what lets you read prices across any sportsbook anywhere.
Betting odds are a price tag on an outcome. When a sportsbook lists the Boston Celtics at -180, that number is the price for a Celtics ticket. The same -180 in decimal odds is 1.56. In fractional odds it's 5/9. All three describe the same bet at the same price.
Underneath the format, every odds line answers two questions. How much do I risk to make a target profit? And what win rate would the bet need to clear to break even? Once you can answer both questions for any line in any format, the rest is just translation. The vocabulary worth knowing before you start is in our sports betting glossary, which has entries for every odds-format term used below.
American odds are the default at every US sportsbook. They're expressed as a positive or negative number anchored to a $100 base. The sign tells you whether the side is a favorite or an underdog. The number tells you the payout.
Favorites carry a minus sign. A team listed at -180 is the favorite. The number is how much you have to bet to profit $100. So -180 means risk $180 to win $100. The bigger the negative number, the heavier the favorite.
Underdogs carry a plus sign. A team listed at +150 is the underdog. The number is how much you'd profit on a $100 stake. +150 returns $150 in profit on $100 risked. The bigger the positive number, the bigger the underdog.
Even money is +100 or -100. When two sides are evenly matched, both lines sit near +100. A pick'em game might list both teams at -110 (the standard juice on a spread), meaning either side requires $110 to win $100. For a deeper breakdown of how American odds work in practice, our moneyline bet guide covers the full math with example payouts.
Best for: US bettors. Every major US sportsbook defaults to American odds.
Watch for: Heavy favorites priced at -300 or worse require huge stakes for small returns. The implied break-even rate on a -500 favorite is 83%. That's a high bar.
Decimal odds are the default in Europe, Canada, Australia, and most of the rest of the world. The number represents your total return per unit wagered, including your original stake. The math is one multiplication.
To calculate your payout: stake × decimal odds = total return.
A $100 bet at 2.50 returns $250 total ($100 stake plus $150 profit). A $100 bet at 1.80 returns $180 total. A $100 bet at 4.00 returns $400 total.
Reading favorites and underdogs. Decimal odds below 2.00 are favorites. Decimal odds above 2.00 are underdogs. 2.00 is even money (the equivalent of +100 American). 1.50 is a strong favorite. 5.00 is a heavy underdog returning four times your stake in profit.
Best for: International bettors, betting exchanges, and anyone who prefers one-step payout math. Many sharp bettors set US sportsbook apps to decimal display for that reason.
Watch for: Decimal odds include your stake in the listed number. A 2.50 line returns 1.50 in profit per dollar staked, not 2.50. New bettors converting from American odds sometimes overestimate winnings because they treat the decimal number as profit instead of total return.
Fractional odds are the traditional format in the UK, Ireland, and horse racing markets worldwide. They're expressed as a ratio: profit over stake. The first number is how much you win, the second is how much you risk.
A 5/1 line (read "five-to-one") means you win $5 in profit for every $1 staked. A $100 bet at 5/1 returns $500 in profit. A 2/1 line returns $200 in profit per $100. A 1/2 line (read "one-to-two") is a favorite: risk $2 to win $1, or risk $100 to win $50 in profit.
Calculating payouts. Multiply your stake by the first number, divide by the second. A $50 bet at 7/2 returns ($50 × 7) ÷ 2 = $175 in profit. A $50 bet at 4/5 (a favorite) returns ($50 × 4) ÷ 5 = $40 in profit.
Even money is 1/1 (or "evens" in UK racing parlance). Favorites have the first number smaller than the second (1/2, 2/5, 4/9). Underdogs have the first number larger (3/1, 5/1, 10/1).
Best for: UK retail sportsbooks, horse racing tickets at tracks like Churchill Downs and Saratoga, and long-shot futures where 50/1 reads more naturally than +5000.
Watch for: Fractions don't simplify the way you might expect. 5/2 and 5/4 are not the same odds. Reading fractional odds at extreme prices like 100/30 (equivalent to +333 American) takes more mental work than either alternative.
Every odds line in any format converts to the same implied probability. Once you can move between formats, you can pull a price off any sportsbook anywhere and know exactly what you're getting.
American to decimal:
American to fractional:
Decimal to American:
A working reference of the same prices written in all three formats:
Most sportsbooks let you switch the displayed format in settings. Worth doing once to see your usual prices written all three ways.
Implied probability is the conversion that turns a price into a percentage. It tells you what win rate a bet needs to clear to break even. Every odds line in every format has an implied probability baked in.
From American odds:
From decimal odds: probability = 1 ÷ decimal. So 2.50 implies 1 ÷ 2.50 = 40%. 1.50 implies 66.7%.
From fractional odds: probability = denominator ÷ (numerator + denominator). So 3/2 implies 2 ÷ 5 = 40%. 1/2 implies 2 ÷ 3 = 66.7%.
Implied probability is what separates intuitive bettors from sharp bettors. Anyone can pick a winner. The sharp question is whether the actual probability of an outcome is higher than the price implies. A bet has positive expected value when the true probability exceeds the implied probability. That's the framework underneath every disciplined betting strategy.
If you add the implied probabilities of both sides of a moneyline, you'll get a number above 100%. That extra percentage is the vig, the sportsbook's built-in margin.
Take a pick'em game where both teams are listed at -110. The implied probability on each side is 110 ÷ 210 = 52.4%. Add them together and you get 104.8%. That extra 4.8% is the sportsbook's cut on a balanced book. A -250 favorite paired with a +200 underdog implies 71.4% + 33.3% = 104.7%. The vig stays in roughly the same range across price levels.
Understanding the vig changes how you read odds. The break-even win rate at -110 isn't 50%, it's 52.4%. That 2.4% gap is the hurdle every spread and total bettor is climbing. Closing line value, line shopping, and beating soft markets are all strategies aimed at chipping away at that vig. Our piece on against the spread covers how this plays out specifically on spread bets.
Knowing how to read odds is step one. Knowing whether your odds reads are actually profitable is step two, and that requires tracking every bet you place.
Pikkit's bet tracker records every settled bet via BookSync regardless of which format your sportsbook displays. Historical odds, stake, implied probability, and realized profit all live in one place. Over a meaningful sample, the patterns become visible: whether you over-bet favorites, whether your underdog plays clear their break-even hurdle, whether your line shopping is actually capturing the prices you think it is.
The more useful long-run metric is closing line value, which compares the odds you got to the closing price on the same market. Consistently beating the close is one of the few honest predictors of long-run profitability, and the measurement doesn't care which format your book used. A +150 bet that closed at +130 beat the close, regardless of whether it displayed as American, decimal (2.50 closing at 2.30), or fractional (3/2 closing at 13/10).
All three odds formats describe the same thing: how much you'll win, how much you'll risk, and what win rate the price implies. American odds are the default in US sportsbooks. Decimal odds are simpler math. Fractional odds are the format on horse racing tickets and UK futures. The conversion math takes thirty seconds to learn and pays off every time you read odds outside your home format.
Once you can read all three, the next layer is implied probability. That's the framework that turns betting from "who do I think wins" into "is the price right for the actual probability." Track every bet you place, study where your reads beat the implied number, and the rest is repetition.
Download Pikkit to track your odds, your win rate, and your closing line value across every sportsbook you bet on.
American odds use a + or − sign anchored to $100. A − sign marks the favorite and tells you how much you have to risk to win $100. A + sign marks the underdog and tells you how much you'd win on a $100 stake. So −180 means risk $180 to win $100, and +150 means win $150 on a $100 bet. The bigger the number in either direction, the more lopsided the matchup.
A +150 line means you'd win $150 in profit on a $100 stake (total payout $250 including your stake back). It implies a 40% probability that the outcome hits. A $50 bet at +150 returns $75 in profit. A $25 bet returns $37.50.
A −200 line means you have to risk $200 to win $100 in profit. It implies a 66.7% probability. A $50 bet at −200 returns $25 in profit. The −200 price translates to 1.50 in decimal odds and 1/2 in fractional.
For positive American odds, divide the number by 100 and add 1 (so +250 becomes 3.50). For negative American odds, divide 100 by the absolute value and add 1 (so −200 becomes 1.50). Decimal odds always include your stake in the listed return, which is why decimal numbers are always 1.00 higher than the equivalent profit multiplier.
Fractional odds are expressed as profit over stake. A 5/1 line means you win $5 in profit for every $1 staked. A 1/2 line means you'd risk $2 to win $1 in profit (or $200 to win $100). To calculate the payout, multiply your stake by the first number and divide by the second.
Implied probability is the percentage chance an odds line assumes. It's the win rate a bet would need to clear to break even at that price. A +150 line implies 40%. A −200 line implies 66.7%. Implied probability is the basis for every expected-value calculation, and it's how sharp bettors decide whether a price is worth playing regardless of which team they think will win.
The excess over 100% is the sportsbook's vig (also called juice or margin). Two sides of a typical −110 spread line sum to 104.8%, with that 4.8% being the book's profit margin on balanced action. Sharper books and bigger markets run tighter vig. Recreational books run wider vig. Line shopping across sportsbooks is one of the few consistent ways to reduce the vig you pay.
None is mathematically better than the others. They all express the same prices. American odds are best if you bet in the US because every major US sportsbook defaults to them. Decimal odds are easiest for quick payout math. Fractional odds are most natural for horse racing and long-shot futures. Bettors using multiple sportsbooks often switch their preferred display format to decimal because the math is faster to compute mentally.
