Three ways to write a price, one number underneath.
The same wager can appear on your screen as -110, as 1.909, or as 10/11, and nothing on the screen tells you those are the same thing. American odds are written around a stake of 100, decimal odds give the total return on one unit, and fractional odds give the profit on its own. All three are wrappers around a single figure, which is the probability the price is demanding of you. This page converts prices in both directions between all three notations, then shows the two places where the notation itself, rather than the price, is what costs you.
American, decimal, and fractional
American odds are built around a stake of 100. A negative price states what you have to risk in order to win 100, so a football side at -150 risks 150 to win 100. A positive price states what a risk of 100 wins, so +150 wins 150 on top of the stake coming back. The sign only tells you which side of even money the price sits on, and the size of the number tells you how far from it.
Decimal odds state the total return on one unit staked, with the stake counted inside the number, so 2.50 returns two and a half units on a one unit wager and one and a half of those are profit. Fractional odds state the profit alone and leave the stake out of it, so 3/2 pays three units of profit on a two unit risk. The gap between the two notations is exactly one unit, which is the whole of what you need to remember to move between them. Decimal is the standard across Europe and Australia, fractional is the traditional convention in British and Irish books and still the default on racing boards, and American is what North American screens show, which is why the same wager stops looking familiar the moment you change countries.
Each notation has its own marker for even money, and learning to spot those markers is most of the skill. Even money is +100 in American, 2.00 in decimal, and 1/1 in fractional. Anything shorter than the marker is a favorite and anything longer is an underdog, in every one of the three. Sitting underneath all of them is a single probability with the sportsbook's margin folded into it, and that probability is what the rest of this page is about.
One price, all the way round
Take a basketball underdog at +150. The rule for a positive price is 1 + O/100, so 150 divided by 100 is 1.5, and adding the stake back gives a decimal of 2.50. Take the stake out again by subtracting one and you have 1.5, written fractionally as 3/2. Implied probability is 1 / decimal, so 1 divided by 2.50 is 40 percent. In money that is a 20 dollar stake returning 50 dollars in total, and the fraction says the same thing from the other end, three units of profit for every two risked, which on 20 dollars is 30 dollars of profit.
Now take the standard football spread price of -110. The rule for a negative price is 1 + 100/|O|, so 100 divided by 110 is 0.909, and the decimal is 1.909. That 0.909 is the fraction, and 100/110 reduces to 10/11, meaning ten units of profit for every eleven risked. Every minus price produces a fraction below one for exactly that reason. One divided by 1.909 is 52.38 percent, which is both what this price implies and the share of these wagers you would have to win to finish level.
The return trip is the same algebra run backwards, and it is worth knowing because plenty of screens offer only one notation. When a decimal is 2.00 or higher, the American price is the decimal minus one, multiplied by 100, so 2.50 goes back to +150. When it is below 2.00, the American price is 100 divided by the decimal minus one, carrying a minus sign, so 1.909 goes back to -110. Fractional to decimal is just the fraction plus one, and fractional straight to probability is the denominator divided by the sum of both numbers, which turns 10/11 into 11 divided by 21, or 52.38 percent again.
American prices cannot be subtracted
The expensive habit is treating American prices as quantities and doing arithmetic on them. They are labels for a ratio rather than positions on a ruler, so two prices written the same distance apart are not the same distance apart in anything that pays. The tell is that the scale has a hole in the middle of it.
Negative and positive prices are produced by two different formulas that meet at a decimal of 2.00, which means -100 and +100 are the same price written twice and no American number exists between them. Subtract -105 from +105 and the apparent gap is 210. In money those two prices are decimal 1.952 and 2.05, a difference of 0.098 per unit staked. Now do the same to -110 and -120 and the gap is 10. Those are decimal 1.909 and 1.833, a difference of 0.076. The gap that looks twenty-one times wider is worth about 1.3 times as much.
The same defect makes prices impossible to average. There is no useful midpoint between -110 and +110, while the midpoint of 52.38 percent and 47.62 percent is 50 percent and is exactly right. How much probability each ten cents is actually buying, which changes depending on where on the board you are standing, is worked through in implied probability, and the reason both sides of a market add up to more than 100 percent belongs to what is juice.
Work in percentages, and pick one notation
The habit that makes any of this useful is a small one. Convert the price to a percentage before you compare it to anything, whether the comparison is across books, across notations, or across sports. Percentages sit on a common scale and American prices do not, so a basketball total at -115 and a baseball underdog at +150 are not comparable as they are written, while 53.49 percent and 40 percent are. The break-even calculator will do it for you, though the arithmetic is short enough to do in your head once the two formulas are familiar.
Then choose one notation and stay inside it. Round trips between notations are not always exact, because screens quote decimals to two places: a decimal shown as 1.91 implies 52.36 percent, while the -110 it stands in for implies 52.38 percent. Two hundredths of a point will never decide a wager, but switching notations in the middle of a comparison is how a rounding difference gets mistaken for a better number at another book.
The percentage is the version of a price a record cannot do without. A record that stores what the screen said gives you a column you cannot total, average, or compare across sports, while a record that stores the converted percentage beside it gives you one you can. That single extra column is what later makes it possible to ask whether the prices you took were any good, which is the whole subject of tracking bets and ROI.
A price you have not converted
Long prices are the ones most often left unconverted, and they are also the ones that read as bargains. A shot at +500 converts to 16.67 percent, which is a wager designed to lose roughly five times in six, so five straight losses on prices like that is the ordinary case rather than a sign that something has gone wrong or is owed back to you. Convert first, decide the stake before the odds are in front of you, and if converting has started to feel like a formality you skip, the responsible gambling page is the right place to stop and read. Betting a number you have not converted is guessing with extra steps.
Reading odds, answered
How do you read betting odds?
Identify the notation first, then convert it to a percentage. American odds are written around a stake of 100, decimal odds give the total return on one unit including the stake, and fractional odds give the profit on its own. Whichever notation is on the screen, the figure that decides anything is the implied probability underneath it, because that is the win rate the price is asking you to beat.
What does -110 mean in betting odds?
A price of -110 means you risk 110 to win 100, so a winning ticket returns 210 in total. The same price is 1.909 in decimal and 10/11 in fractional, and it implies a probability of 52.38 percent. That 52.38 percent is also the share of wagers you have to win at that price to come out level, which is why -110 on both sides of a market is not a coin flip proposition.
What is +150 in decimal and fractional odds?
A price of +150 is 2.50 in decimal and 3/2 in fractional. The decimal includes the returned stake and the fraction does not, which is the single difference between the two notations and the thing most often misread. Dividing one by the decimal gives 40 percent, and reading the fraction as three units of profit for every two risked gives the same answer from the other end.
How do you convert American odds to decimal odds?
For a positive American price, divide it by 100 and add one, so +200 becomes 3.00. For a negative price, divide 100 by the number without its sign and add one, so -200 becomes 1.50. Going the other way, subtract one from the decimal and multiply by 100 when the decimal is 2.00 or higher, and divide 100 by the decimal minus one when it is below 2.00 and write the result with a minus sign.
What are fractional odds?
Fractional odds state profit against stake, so 3/2 wins three units for every two risked and 10/11 wins ten units for every eleven risked, with the stake returned separately in both cases. A fraction greater than one is an underdog, a fraction less than one is a favorite, and 1/1 is even money. The quickest way to a probability from a fraction is to divide the denominator by the sum of both numbers, which turns 10/11 into 11 divided by 21, or 52.38 percent.
Is one odds format better than another?
No format carries information the others lack, so the choice is convenience rather than substance, with one caveat: a decimal is normally shown to two places while an American price is exact, so the American number is the safer one to store. Decimal is the easiest to work with, because implied probability is one divided by the decimal and parlay legs multiply together directly. American is what North American screens show, and fractional is the hardest to compare at a glance because the denominators are not standardized.
Does a bigger minus number mean a better chance of winning?
A bigger minus number does imply a higher chance, since -300 implies 75 percent where -150 implies 60 percent. It does not imply a better bet, because the price gets shorter in step with the chance and you are paying for every point of that extra probability. A heavy favorite is only worth backing when your own estimate sits above the percentage the price already demands.
Can the same event be a different price in different formats at the same book?
The two displayed prices are never two different wagers, and the settlement is identical whichever notation the screen happens to use. What differs is precision: American odds are exact whole numbers, while a decimal is normally truncated to two places, so the decimal is the lossy direction of the conversion. Treat any tiny disagreement between the two as a display artefact rather than as one book quietly offering a better number.
Read every price the same way
The break-even calculator turns any price into the win rate it demands, and every board we publish shows the model number and the market price already converted, so nothing on the screen is left in a notation you have to translate first.