An odds converter rewrites one price in the other two odds formats and shows the chance that price implies. Type 2.50, 3/2 or +150 into the converter above and each gives the same answer: decimal 2.50, fractional 3/2, American +150 and an implied chance of 40.0%.
This page explains what the converter does with what you type, which format is used where, how to convert by hand, and which slips lead to wrong answers. It changes the format of a price only. It does not say whether a price is fair.
What does an odds converter do?
An odds converter changes how a price is written without changing the price. Decimal, fractional and American odds are three notations for the same thing: what a winning wager returns compared with the stake. The converter also divides 1 by the decimal figure to show the chance the price implies, which still includes the bookmaker’s margin.
The converter above takes one price in any format. It has three buttons, Decimal, Fractional and American, that choose which format appears as the large answer. A line under the answer always lists all three, and a bar shows the implied chance. It runs in your browser and nothing you type is sent anywhere.
Converting a price is a different job from working out a payout. If you want to see what a particular stake returns, the planned odds calculator takes a stake and a price and gives profit and total return. The converter only handles the price itself.
How do you use this odds converter?
Type one price into the box in any format, such as 2.50, 3/2 or +150, and the result updates as you type. Use the Decimal, Fractional and American buttons to choose which format is shown as the large answer. The line beneath always lists all three formats, and the bar shows the implied chance.
- Type the price. Use a decimal number above 1 (2.50), a fraction with a slash (3/2) or an American number with its sign (+150 or -200).
- Pick the large answer. Press Decimal, Fractional or American. This changes only the big number, not the price.
- Read the line below it. It shows the same price in all three formats, so you can copy whichever one you need.
- Read the implied chance. The bar and percentage show 100 divided by the decimal odds. It is the chance the price suggests, margin included.
- Fix any message. If the box shows a message, the price is outside the format. Correct it and the answer returns.
What will the converter accept?
The converter reads three kinds of price and rejects a few things that look like odds but are not valid. The table below lists what happens with typical entries, so you can see why a message appears.
| You type | Result | Why |
|---|---|---|
| 2.50 | Accepted as decimal 2.50 | Decimal odds must be above 1. |
| 1.00 or 0.80 | Rejected | A decimal price of 1 or less would return no more than the stake. |
| 3/2 | Accepted as 3/2 | Fractions need numbers on both sides of a slash. |
| +150 or -200 | Accepted | American odds need a plus or minus sign. |
| +100 or -100 | Both accepted as 2.00 | Both mean even money. |
| +50 or -50 | Rejected | American odds between -100 and +100 are not used in the format. |
| 150 with no sign | Read as decimal 150.00 | Without a sign the number is treated as decimal, which implies about 0.7%. |
| 2,50 | Accepted as decimal 2.50 | A comma is read as the decimal point. |
Why do 1.91 and -110 show different fractions?
Typing -110 gives decimal 1.91 and fractional 10/11, but typing 1.91 gives -110 and 91/100. The reason is rounding. A price of -110 is exactly 1.9091 in decimal, and 10/11 is the closest simple fraction to that. The figure 1.91 is a rounded version, so its closest fraction, with a bottom number of up to 100, is 91/100.
How do decimal, fractional and American odds compare?
All three formats describe the same price, but they count from different starting points. Decimal shows the total return per 1 staked, stake included. Fractional shows the profit compared with the stake. American shows the profit on 100 staked when positive, or the stake needed to win 100 when negative.
| Format | What the number means | Even money | A short price (favorite) | A long price (underdog) |
|---|---|---|---|---|
| Decimal | Total return per 1 staked, stake included | 2.00 | 1.50 | 4.00 |
| Fractional | Profit compared with the stake | 1/1 | 1/2 | 3/1 |
| American | Profit on 100 if positive; stake needed to win 100 if negative | +100 or -100 | -200 | +300 |
Which format is used where?
The formats follow regional habits. A trial run by the Behavioural Insights Team with the Ohio Casino Control Commission describes American odds as the current default on all digital US sportsbooks, with decimal (European) and fractional (British) odds more popular elsewhere. A 2022 paper in the Annals of Operations Research likewise labels decimal odds as the European format, and the documentation for an R package that converts odds notes that fractional odds are commonly used by bookmakers in the UK.
Why does the format matter?
The same price can feel different in a different format. In the Behavioural Insights Team trial, which had more than 4,000 participants in the US, people shown American odds alone chose the riskier option more often than people shown other presentations. On average they also estimated about a 53% chance of winning a same-game parlay whose odds implied about 4%. Showing the implied chance next to the odds reduced how many risky options people chose. That is why the converter shows the chance beside the price.
What about Hong Kong, Malay and Indonesian odds?
The same R package documentation also lists Hong Kong, Malaysian and Indonesian odds. This converter does not read them, so convert such a price to decimal first, then enter the decimal figure.
What are the common prices in every format?
The table below lists 25 common prices written as fractions, with the matching decimal and American figures and the chance each implies. Every row is what the converter shows when you type the fraction. Prices whose first number is smaller than the second are called odds-on.
| Fractional | Decimal | American | Implied chance |
|---|---|---|---|
| 1/10 | 1.10 | -1000 | 90.91% |
| 1/5 | 1.20 | -500 | 83.33% |
| 1/4 | 1.25 | -400 | 80.00% |
| 1/3 | 1.33 | -300 | 75.00% |
| 4/9 | 1.44 | -225 | 69.23% |
| 1/2 | 1.50 | -200 | 66.67% |
| 4/5 | 1.80 | -125 | 55.56% |
| 10/11 | 1.91 | -110 | 52.38% |
| 1/1 | 2.00 | +100 | 50.00% |
| 6/5 | 2.20 | +120 | 45.45% |
| 5/4 | 2.25 | +125 | 44.44% |
| 3/2 | 2.50 | +150 | 40.00% |
| 7/4 | 2.75 | +175 | 36.36% |
| 2/1 | 3.00 | +200 | 33.33% |
| 9/4 | 3.25 | +225 | 30.77% |
| 5/2 | 3.50 | +250 | 28.57% |
| 3/1 | 4.00 | +300 | 25.00% |
| 7/2 | 4.50 | +350 | 22.22% |
| 4/1 | 5.00 | +400 | 20.00% |
| 5/1 | 6.00 | +500 | 16.67% |
| 6/1 | 7.00 | +600 | 14.29% |
| 8/1 | 9.00 | +800 | 11.11% |
| 10/1 | 11.00 | +1000 | 9.09% |
| 50/1 | 51.00 | +5000 | 1.96% |
| 100/1 | 101.00 | +10000 | 0.99% |
American lines usually come in steps such as -110 or -120, so here are common ones. The exact decimal is shown to four places, because the implied chance uses it.
| American | Decimal (shown) | Decimal (exact) | Fractional | Implied chance |
|---|---|---|---|---|
| -110 | 1.91 | 1.9091 | 10/11 | 52.38% |
| -105 | 1.95 | 1.9524 | 20/21 | 51.22% |
| -120 | 1.83 | 1.8333 | 5/6 | 54.55% |
| -150 | 1.67 | 1.6667 | 2/3 | 60.00% |
| -200 | 1.50 | 1.5000 | 1/2 | 66.67% |
| -250 | 1.40 | 1.4000 | 2/5 | 71.43% |
| -300 | 1.33 | 1.3333 | 1/3 | 75.00% |
| +120 | 2.20 | 2.2000 | 6/5 | 45.45% |
| +150 | 2.50 | 2.5000 | 3/2 | 40.00% |
| +200 | 3.00 | 3.0000 | 2/1 | 33.33% |
| +300 | 4.00 | 4.0000 | 3/1 | 25.00% |
| +500 | 6.00 | 6.0000 | 5/1 | 16.67% |
How do you convert odds by hand?
To convert by hand, change the starting price into decimal odds, then work out the format you want from the decimal figure. Decimal is the hub because it is one number that already includes the stake. Four short rules cover every route.
- Fractional to decimal: divide the top number by the bottom number, then add 1. For 5/2: 5 ÷ 2 = 2.5, plus 1 gives 3.50.
- Positive American to decimal: divide by 100, then add 1. For +150: 150 ÷ 100 = 1.5, plus 1 gives 2.50.
- Negative American to decimal: divide 100 by the number without its minus sign, then add 1. For -200: 100 ÷ 200 = 0.5, plus 1 gives 1.50.
- Decimal to the others: subtract 1 to get the profit per 1 staked. Write it as a fraction for fractional odds. For American, if the decimal is 2.00 or more, multiply the profit by 100 and add a plus sign. If it is below 2.00, divide 100 by the profit and add a minus sign.
- Decimal to implied chance: divide 1 by the decimal odds and write the result as a percentage.
Example: convert 7/2. Decimal: 7 ÷ 2 = 3.5, plus 1 gives 4.50. The profit is 3.5 per 1 staked, and 3.5 × 100 gives +350. Implied chance: 1 ÷ 4.50 = 0.2222, or 22.22%. The converter shows the same three figures.
Example: convert -250. Decimal: 100 ÷ 250 = 0.4, plus 1 gives 1.40. The profit is 0.4 per 1 staked, which is 2/5 as a fraction. Implied chance: 1 ÷ 1.40 = 0.7143, or 71.43%. A short price like this implies a chance well above 50%.
Example: convert the decimal price 1.80. The profit is 0.80 per 1 staked, which is 4/5. Because 1.80 is below 2.00, the American figure is 100 ÷ 0.80 = 125, written -125. Implied chance: 1 ÷ 1.80 = 0.5556, or 55.56%.
Why is the implied chance higher than the real chance?
The implied chance is higher than the real chance because the price includes the bookmaker’s margin. If you add up the implied chances of every outcome in one market, the total is above 100%. The amount over 100% is the margin, also called the overround or vig, and it is how the bookmaker is paid.
A paper on modelling football scores from bookmakers’ odds states that the sum of the inverse odds for a single match needs to be greater than one, and that bookmakers take roughly 5% to 10%. A study of betting market efficiency describes the excess probability as overround and says the odds need an adjustment before they can be used as winning probabilities.
Example: a two-way market where both sides are priced at -110. Each side implies 110 ÷ 210 = 52.38%. The two together make 104.76%, so the margin is 4.76 percentage points. If the two sides were truly equal at 50% each, a 10-unit wager at 1.9091 would return 19.09 half the time, so the average result is 0.5 × 19.09 – 10 = -0.45 units. That is about 4.5% of the stake, which is the cost built into the price.
Example: Team A is 1.80 and Team B is 2.10. The implied chances are 55.56% and 47.62%, which total 103.17%. To remove the margin in the simplest way, divide each by the total: 53.85% and 46.15%. This basic method treats the margin as spread evenly across both sides, so it is an estimate, not a true probability.
If you notice that cost adding up, or you want to set a spending limit before you play, the Safer play toolkit explains practical steps, and the planned article on what overround means will take the margin maths further.
What mistakes do people make when converting odds?
Most wrong answers come from a few slips: forgetting the stake in decimal odds, flipping a fraction, misreading American signs, rounding too early, and treating the implied chance as the real chance. The table shows each slip with the correct reading.
| Mistake | What goes wrong | Correct reading |
|---|---|---|
| Reading 5/2 as 2.50 | The fraction is profit per 1 staked, so the stake is missing. | 5/2 is 3.50 in decimal and +250 in American. |
| Flipping 2/5 and 5/2 | They look alike but are opposite prices. | 2/5 is odds-on: 1.40, -250, 71.43%. 5/2 is 3.50, +250, 28.57%. |
| Treating decimal as profit | Decimal 2.50 is the total returned, stake included. | Stake 1 returns 2.50, so the profit is 1.50. |
| Reading +150 as a 150 stake | The number is the profit on a 100 stake, not the stake. | Stake 100 returns 250 in total: 150 profit plus the stake. |
| Reading -200 as a 200% chance | The minus sign means the stake needed to win 100. | -200 implies 66.67%. |
| Calling 1.91 the same as -110 | -110 is exactly 1.9091, so rounding hides a small gap. | Use 10/11 or 1.9091 when you need the exact figure. |
| Dropping the sign | The converter reads 150 as decimal 150.00. | Type +150 to mean the American price. |
| Treating implied chance as the real chance | The price contains the bookmaker’s margin. | The real chance is usually lower for each side. |
How do you turn a percentage into odds?
To turn a percentage into odds, divide 100 by the percentage to get decimal odds, then convert as usual. A 40% chance gives 100 ÷ 40 = 2.50, which is 3/2 and +150. This is the reverse of the implied chance, and it gives the price with no margin in it.
| Chance | Decimal | Fractional | American |
|---|---|---|---|
| 20% | 5.00 | 4/1 | +400 |
| 25% | 4.00 | 3/1 | +300 |
| 40% | 2.50 | 3/2 | +150 |
| 50% | 2.00 | 1/1 | +100 |
| 75% | 1.33 | 1/3 | -300 |
| 80% | 1.25 | 1/4 | -400 |
Real prices are shorter than these because of the margin, so do not expect a price to match a chance exactly.
What should you do next?
Check a price you have seen by typing it into the converter, then look at the implied chance. For a payout from a given stake, use the planned odds calculator. For several prices combined, the planned parlay calculator multiplies the decimals.
We recomputed every figure on this page from the formulas shown, and our editorial standards explain how we check numbers and sources. A price is only a way of writing a cost, and it does not make an outcome more or less likely.
How to read the result
The large answer is the price in the format you pick with the Decimal, Fractional and American buttons. The line under it always shows all three. Decimal is the total return per 1 staked, stake included, so 2.50 returns 2.50. Fractional is profit compared with the stake, so 3/2 pays 3 profit per 2 staked. American is the profit on 100 staked when positive, such as +150, and the stake needed to win 100 when negative, such as -200. The bar shows the chance the price implies, which includes the bookmaker's margin. Short prices (decimal below 2.00, American negative, fractions like 1/2) imply more than 50%. Long prices imply less than 50%. A message under the box means the entry is outside the format.
How it is calculated
Every entry is first turned into decimal odds, d. Decimal entries are used as typed and must be above 1. A fraction a/b becomes 1 + a / b. A positive American number +A (A at least 100) becomes 1 + A / 100. A negative American number -A (A at least 100) becomes 1 + 100 / A. American numbers between -100 and +100 are rejected. From d the converter shows: decimal, rounded to 2 places; fractional, the closest simple fraction to (d - 1), trying bottom numbers from 1 to 100 and keeping the smallest error; American, +round((d - 1) x 100) when d is 2.00 or more, otherwise -round(100 / (d - 1)). The implied chance is 100 / d percent, shown to 1 decimal place in the bar and 2 places in the Formula note.
Worked example
Worked example
With the default entry +150 and the Decimal button selected, the large answer is 2.50. The line reads: Decimal 2.50. Fractional 3/2. American +150. The chance the price implies is 40.0%, and the Formula note reads 1 / 2.50 = 40.00%. Press Fractional and the large answer becomes 3/2. Working: 150 / 100 + 1 = 2.50; 2.50 - 1 = 1.5, which is 3/2; 100 / 2.50 = 40%. A 10-unit stake at this price returns 25 units if it wins, which is 15 profit plus the stake.
Limits
The converter changes the format of one price and works out the chance that price implies. It does not say whether a price is fair, and the implied chance still includes the bookmaker's margin, so it is higher than the real chance. It does not take a stake, so it does not give a payout, and it does not combine prices, remove margin, or allow for fees, tax, dead heats or rule differences. Fractions are shown as the closest simple fraction with a bottom number of 100 or less, so a rounded decimal such as 1.91 shows 91/100 while -110 shows 10/11. American numbers between -100 and +100 and decimals of 1 or less are rejected. Prices extremely close to 1.00 are shown to two decimals. Enter real prices, since fractions with a zero on either side are not valid prices. Hong Kong, Malay and Indonesian odds are not read. Results are estimates of a price's meaning, not predictions.