How to Read Betting Odds: American, Decimal, Fractional
Learn how to read betting odds in American, decimal and fractional format, convert between all three, and turn any price into a probability and a payout.
By Lines & Limits Editorial9 min read
Betting odds are a price. They tell you two things at once: how much you get paid if you are right, and what probability the sportsbook has priced the outcome at. Everything else in betting is built on top of those two readings.
There are three formats — American, decimal and fractional — and they all express the same information in different notation. Once you can move between them and convert any of them into a percentage, you can read any board in the world.
How American odds work
American odds are quoted as a number with a plus or minus sign, always relative to a base of 100.
- A negative number is what you must risk to win $100 in profit. At −110, you risk $110 to win $100.
- A positive number is what you win if you risk $100. At +150, you risk $100 to win $150.
The number is never a payout on its own. It is a ratio, scaled to 100 so that prices are easy to compare at a glance. You can bet any amount you like; the ratio holds.
A price of −110 and a price of +150 are describing very different outcomes. The first is a favorite-ish price where you must lay out more than you stand to win. The second is an underdog price where you win more than you risk. The dividing line is +100 (also written as “even money”), where risk and profit are equal.
Reading a negative price
At −200, you risk $200 to win $100. A winning $50 bet returns $75: your $50 back plus $25 profit. The bigger the negative number, the shorter the price and the more likely the outcome is being treated as.
Reading a positive price
At +300, you risk $100 to win $300. A winning $50 bet returns $200: your $50 back plus $150 profit. The bigger the positive number, the longer the price and the less likely the outcome is being treated as.
Decimal odds: the total return multiplier
Decimal odds express the total return per 1 unit staked, stake included. Odds of 2.50 mean a winning $100 bet returns $250 — $150 profit plus your $100 back.
That “stake included” part is the only thing that trips people up. Decimal 2.00 is even money, not double your money in profit. Anything below 2.00 is a favorite; anything above is an underdog.
The rest of the world uses decimal because the arithmetic is trivial:
total return = stake × decimal oddsprofit = stake × (decimal odds − 1)implied probability = 1 ÷ decimal odds
That last line is why decimal is the format worth learning even if you only ever bet in a US app. Decimal 1.91 immediately gives you 1 ÷ 1.91 = 52.36%, which is close enough to the exact 52.38% for −110 that you can do it in your head.
Fractional odds: profit per unit staked
Fractional odds are the traditional British format and express profit relative to stake. Odds of 3/2 (“three to two”) pay $3 profit for every $2 risked. Odds of 1/2 (“one to two”, or “odds-on”) pay $1 profit for every $2 risked.
To convert:
decimal = (numerator ÷ denominator) + 1implied probability = denominator ÷ (numerator + denominator)
So 10/11 is (10 ÷ 11) + 1 = 1.9091 decimal, and 11 ÷ (10 + 11) = 52.38% implied. That is exactly American −110 written a different way.
Fractional odds are awkward once prices stop landing on clean fractions, which is why they have largely been replaced by decimal everywhere except UK horse racing.
Conversion formulas between all three formats
These are the only formulas you need. Everything else is a rearrangement.
American to decimal
- Positive:
decimal = 1 + (american ÷ 100) - Negative:
decimal = 1 + (100 ÷ |american|)
Decimal to American
- If decimal ≥ 2.00:
american = (decimal − 1) × 100 - If decimal is under 2.00:
american = −100 ÷ (decimal − 1)
Decimal to fractional
fraction = decimal − 1, reduced. Decimal 2.20 → 1.20 → 6/5.
Anything to implied probability
- From decimal:
implied % = 1 ÷ decimal - From positive American:
implied % = 100 ÷ (american + 100) - From negative American:
implied % = |american| ÷ (|american| + 100)
The conversion table you will actually use
Most of the prices you meet sit on a short ladder. Learn this table and you can read a board without doing arithmetic.
| American | Decimal | Fractional | Implied probability | Profit on $100 |
|---|---|---|---|---|
| −200 | 1.50 | 1/2 | 66.67% | $50.00 |
| −150 | 1.667 | 2/3 | 60.00% | $66.67 |
| −110 | 1.909 | 10/11 | 52.38% | $90.91 |
| +100 | 2.00 | 1/1 | 50.00% | $100.00 |
| +120 | 2.20 | 6/5 | 45.45% | $120.00 |
| +150 | 2.50 | 3/2 | 40.00% | $150.00 |
| +200 | 3.00 | 2/1 | 33.33% | $200.00 |
| +300 | 4.00 | 3/1 | 25.00% | $300.00 |
Every row is the same statement in four notations. The last column is profit only — add your stake back to get the total return.
How do you turn odds into implied probability?
Implied probability is the win rate at which a price breaks exactly even. It is the single most useful number you can extract from a board, and it takes one line of arithmetic.
Worked example, −110:
110 ÷ (110 + 100) = 110 ÷ 210 = 0.523809… = 52.38%
So a −110 bet needs to win 52.38% of the time to break even. Win less often than that and you lose money; win more and you make money, before considering anything else.
Worked example, +150:
100 ÷ (150 + 100) = 100 ÷ 250 = 0.40 = 40.00%
A +150 bet needs to hit 40% of the time. That is the whole concept: a longer price does not mean a better bet, it means a lower required hit rate. There is a full treatment in our guide to implied probability in betting, including how to strip the margin back out.
Why the two sides add up to more than 100%
Take a standard total priced −110 on the over and −110 on the under. Convert both:
- Over:
110 ÷ 210 = 52.38% - Under:
110 ÷ 210 = 52.38% - Sum:
52.38% + 52.38% = 104.76%
Two mutually exclusive outcomes cannot have a combined probability of 104.76%. The extra 4.76% is the overround — the margin the sportsbook has built into the pair of prices. That margin is the reason betting is a negative-expectation activity by default, and it is explained in full in what the vig is and how it is calculated.
The practical consequence: you can never read a single price in isolation and call it a probability. You read both sides, add them, and only then do you know how much of what you are looking at is opinion and how much is fee.
The same logic scales badly in your favor when you combine bets. Each leg of a parlay carries its own margin, and multiplying legs multiplies the fee — see why parlay math works against you.
Payout arithmetic: exact numbers
Convert to decimal, multiply by stake. That is the entire method.
| Bet | Decimal | Total return | Profit |
|---|---|---|---|
| $25 at −110 | 1.9091 | $47.73 | $22.73 |
| $25 at +150 | 2.50 | $62.50 | $37.50 |
| $50 at −110 | 1.9091 | $95.45 | $45.45 |
| $100 at −150 | 1.6667 | $166.67 | $66.67 |
| $20 at +120 | 2.20 | $44.00 | $24.00 |
| $110 at −110 | 1.9091 | $210.00 | $100.00 |
The last row is the definition of −110 stated as a transaction: risk 110, get 210 back, net 100.
Note that $25 at −110 returns $47.73, not $50. You risked $25 and won $22.73. The gap between what you risked and what you won is the visible face of the margin.
The four mistakes that cost beginners the most
Treating decimal odds as profit. Decimal 3.00 is $200 profit on a $100 stake, not $300. The stake is inside the number.
Comparing a favorite’s price to an underdog’s price. −150 and +130 are not competing offers on the same thing. They are two sides of one market and both are shaded against you.
Assuming a shorter price is safer. A −400 favorite has a 20% implied chance of losing. Over a season of −400 bets, that arrives regularly, and each loss costs four times what a win pays.
Reading the number and ignoring the juice. A spread of −3 at −105 and the same −3 at −120 look almost identical on a screen. One needs a 51.22% win rate to break even, the other needs 54.55%. That is a bigger difference than most people’s opinions about the game.
A fast way to compare two prices
Convert both to break-even percentages and subtract. The gap is the extra win rate one price demands of you. Between −105 and −120 that gap is 54.5455% − 51.2195% = 3.33 percentage points, which on a coin flip is the difference between losing 2.38% of everything you stake and losing 8.33%.
That comparison takes ten seconds and it works on any two prices in any format, which makes it the most useful habit in this article.
Reading a full board
A typical game screen shows three prices per team, and each one is a different question. The spread and total are usually priced near −110 on both sides; the moneyline is priced to reflect the raw likelihood of each team winning, so it will be lopsided in a mismatch. Our breakdown of moneyline, spread and total bets covers what each market is actually asking.
What matters for reading odds is that the format never changes. A −110 spread, a −450 moneyline and a +2200 futures price are all the same notation, and all three convert with the same two formulas.
What odds do not tell you
Odds are the market’s price, weighted by what the sportsbook is holding. They are not a prediction, and they are not a guarantee that the market is right. A −300 favorite loses roughly a quarter of the time by the market’s own numbers, and that is the market working correctly, not failing.
They also do not tell you how much to bet. Price and stake are separate decisions, and conflating them is the most common way recreational bettors lose money faster than the margin alone would cost them — see bankroll management and staking.
The next step after reading a price
Once a price converts cleanly to a percentage, the useful question stops being “what does this pay?” and becomes “does the payout match how often I think this happens?” That comparison is expected value, and it is the only framework in betting that answers whether a bet is worth making rather than how much it returns.
Start by doing the conversion on every bet you place for a week, before you place it. Not to find edges — you probably will not find any — but because you will notice how often the number you are being charged is worse than the number you assumed.
Frequently asked questions
What does -110 mean in betting?
It means you must risk $110 to win $100 in profit. A winning $110 bet at −110 returns $210 total: your $110 stake plus $100 profit. In decimal format that is 1.91, and it carries an implied probability of 52.38%, which is the win rate you need just to break even at that price.
What does +150 mean in betting odds?
A +150 price pays $150 in profit for every $100 you risk. A winning $100 bet returns $250 total. In decimal format that is 2.50 and in fractional format 3/2. The implied probability is 40%, meaning the price is built for an outcome expected to happen about 4 times in 10.
Are decimal odds better than American odds?
Neither is better; they carry identical information. Decimal is easier to work with because the number is already a multiplier: stake times decimal equals total return, and 1 divided by decimal gives you the implied probability instantly. American odds are the default in US sportsbooks, so most US bettors read both.
How do you calculate a payout from betting odds?
Convert the price to decimal, then multiply by your stake. That gives your total return including the stake. For example, $40 at +120 is 40 × 2.20 = $88 back, which is $48 profit. At −140, $40 × 1.714 = $68.57 back, or $28.57 profit.
Why do both teams have negative odds sometimes?
On a point spread or a total, both sides are usually priced around −110 because the handicap is designed to make the two outcomes roughly equally likely. The book charges a margin on each side, which is why both prices sit below even money instead of both being +100.
Do better odds mean a better bet?
Not by itself. A longer price means a lower implied probability, not a better deal. A bet is good only when your estimate of the true probability is higher than the implied probability in the price, after accounting for the margin baked into both sides of the market.