Odds Converter

An odds converter for a single selection: fractional, decimal and American (moneyline) odds and the implied probability, each converted into the others, plus what a stake would return if it wins.

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How do you convert odds to a probability?

Convert the odds to decimal form and divide 1 by them: decimal 3.50 (fractional 5/2, American +250) implies 1 ÷ 3.50 = 28.57%. The figure includes the bookmaker's margin, so it is slightly higher than the price would be in a fair market.

Cost: Free, no limits
Upload: None — runs on your device
Sign-up: Not required
Works offline: Yes, once loaded

How to convert odds to probability

Choose the format you have
Fractional, Decimal, American or Probability. Each tab keeps its own value.
Type the odds
For example 5/2, evens, 3.50, +250, -110 or 40%.
Read the other formats
All four formats appear together. Add a stake to see the total return and profit if the selection wins.

Examples

5/23.50 · +250 · 28.57%
-11010/11 · 1.91 · 52.38%
The standard price on each side of an American point-spread bet.
25%3/1 · 4.00 · +300
The fair odds for a one-in-four chance.

Key features of the Odds Converter

Fractional, decimal and American odds converted into each other
Implied probability from any odds, and odds from a probability
Exact fractional odds plus the nearest simple fraction
Accepts evens, 5-2 and 5 to 2 as well as 5/2
Total return and profit on a stake you enter

What it converts

Odds formats

Fractional (5/2, 5-2, evens)
Decimal (3.50)
American / moneyline (+250, -200)
Implied probability (28.57%)

Returns

Total return on a stake
Profit on a stake

When should you use this?

Comparing prices quoted in different formats by UK, European and US bookmakers.
Seeing the implied probability behind a price before deciding whether it is good value.
Learning how fractional, decimal and moneyline odds relate.

Limitations

It handles one selection at a time, so it cannot work out a whole market's overround — add up the implied probabilities of each outcome yourself.
Returns assume a single win bet with the stake returned, and no tax, commission, each-way terms or rule 4 deductions.
Decimal, American and probability results are rounded to two decimal places.
This is general information, not financial advice.

Troubleshooting

American odds between -100 and +100 are rejected

They do not exist: American odds start at +100 or -100 (evens) and move away from there.

Decimal odds of 1 or less are rejected

Decimal odds include the stake, so they are always more than 1. 1.00 would return only your stake.

Common mistakes to avoid

Reading implied probability as the true chance. It is the price's chance, margin included.
Forgetting that decimal odds include the stake. 3.50 returns 3.50 per unit staked, of which 2.50 is profit.
Treating -110 and +110 as close. -110 is a short price (1.91); +110 is longer than evens (2.10).

Pro tips

Tips for better results

Value
Lower implied probability means a better price
Compare prices as implied probabilities: the lower figure for the same outcome is the better price.
Margin
Sum a market's probabilities to see the margin
Add up the implied probabilities of every outcome in a market to see the bookmaker's margin; the closer to 100%, the fairer the market.
Budget
Set the stake before the odds, within what you can lose
Decide your stake before you look at the odds, and keep it within a budget you can afford to lose.

Three ways of writing the same price

Fractional odds, traditional in the UK and Ireland, give the profit against the stake: 5/2 means £5 profit for every £2 staked. Decimal odds, used across Europe, Australia and most betting exchanges, give the total return per unit staked, stake included, so 5/2 is 3.50. American odds, also called moneyline odds, are based on 100: a plus figure is the profit on a 100 stake (+250), and a minus figure is the stake needed to win 100 (-200).

Every conversion goes through decimal odds. Fractional a/b becomes 1 + a/b; American +A becomes 1 + A/100 and -A becomes 1 + 100/A. Evens — 1/1, 2.00 or +100 — is the point where American odds switch sign.

Implied probability and the bookmaker's margin

To convert odds to probability, divide 1 by the decimal odds: 3.50 implies 1 ÷ 3.50 = 28.57%. That is the chance the price would be fair at, not the real chance of the event. Bookmakers build in a margin, so the implied probabilities of every outcome in a market add up to more than 100%. In a two-way market priced at 10/11 on both sides, each side implies 52.38%, a total of 104.76% — the extra 4.76% is the overround. This converter takes one selection at a time, so it shows the implied probability with the margin still in it.

Bet within your means

Odds describe a price, not a likely result. Set a budget before you bet and stop when it is spent. If gambling stops being fun, free confidential support is available from BeGambleAware in the UK and the 1-800-GAMBLER helpline in the US.

Privacy

The Odds Converter runs entirely in your browser. What you enter and the result it produces stay on your own device — nothing is sent anywhere, because nothing needs to be.

You can confirm this rather than take our word for it: open your browser’s developer tools, watch the Network tab, and use the tool. No request carries your input. It also keeps working with the connection off.

Details are in the privacy policy.

What next?

Percent, decimal and fraction in any direction.

Convert a probability to a fraction

Odds Converter — questions

How do I convert odds to probability?

Turn the odds into decimal form and divide 1 by them, then multiply by 100. Decimal 4.00 is 25%; fractional 5/2 is 2 ÷ (5 + 2) = 28.57%; American -200 is 200 ÷ 300 = 66.67%.

How do I convert fractional odds to decimal odds?

Divide the first number by the second and add 1 for the returned stake: 5/2 is 2.5 + 1 = 3.50, and 1/2 is 0.5 + 1 = 1.50.

What do plus and minus mean in American odds?

A plus figure is the profit on a 100 stake, so +250 wins 250 for every 100 staked, the price for an outsider. A minus figure is what you must stake to win 100, so -200 means staking 200 to win 100, the price for the side expected to win.

Why do the probabilities in a market add up to more than 100%?

Because of the bookmaker's margin, or overround. The odds are set a little shorter than fair on every outcome, so their implied probabilities total more than 100% and the difference is the bookmaker's expected profit.

Why is 1.91 shown as 91/100 and not 10/11?

1.91 is exactly 91/100 in fractional odds. The usual 10/11 is 1.909 when rounded more finely, so the converter shows 10/11 as the nearest simple fraction underneath rather than pretending the two are identical.

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