Odds Converter

How to Use the Betting Odds Calculator

Enter a value in any one of the available fields: American, Fractional, Decimal, or Implied Probability. The calculator will automatically convert it into the other supported formats.

You can also enter a Bet Amount to see the potential return:

• To Win shows your potential profit, excluding your original stake.
• Payout shows the total amount returned if the bet wins, including your original stake.

For example, if you enter Decimal odds of 2.50 and a $100 bet, the calculator shows:

• To Win: $150
• Payout: $250

The calculator uses these formulas:

Profit = Stake × (Decimal Odds − 1)

Total Payout = Stake × Decimal Odds

The $ symbol is only used for display. The calculation is currency-independent, so the same maths applies to pounds, euros and other currencies.

Actual returns can differ in some cases because of void bets, dead-heat rules, commissions, taxes, or market-specific settlement rules.

Betting Odds Formats Explained

Bookmakers can show the same betting price in different formats. The three formats supported by our calculator are Decimal, Fractional, and American odds. They look different but can represent the same betting price.

Decimal odds show the total return for every unit staked, including the original stake. Odds of 2.50, for example, represent a total return of 2.50 units for every 1 unit staked.

Fractional odds show potential profit in relation to the stake. Odds of 3/2 mean 3 units of potential profit for every 2 units staked. The original stake is returned separately if the bet wins.

American odds use positive or negative numbers. Positive odds show how much profit a $100 stake can produce. For example, +150 means $150 in potential profit from a $100 stake. Negative odds show how much must be staked to make $100 in profit. At -200, a $200 stake would produce $100 in potential profit.

The same betting price can therefore appear in several ways:

Changing the format does not change the value of the odds. For example, +150, 3/2, and 2.50 all represent the same betting price.

How Odds Conversion Works

The Odds Converter uses decimal odds as the common reference value. When you enter American odds, Fractional odds, or Implied Probability, the value is converted to decimal odds first. The calculator then uses that decimal value to calculate the other formats.

Fractional to Decimal

Divide the numerator by the denominator and add 1:

Decimal Odds = (Numerator / Denominator) + 1

For fractional odds of 3/2:

(3 / 2) + 1 = 2.50

So 3/2 is equal to decimal odds of 2.50.

American to Decimal

The formula depends on whether the American odds are positive or negative.

For positive American odds:

Decimal Odds = (American Odds / 100) + 1

For +150:

(150 / 100) + 1 = 2.50

For negative American odds:

Decimal Odds = (100 / |American Odds|) + 1

The vertical bars mean that we use the absolute value of the odds without the negative sign.

For -200:

(100 / 200) + 1 = 1.50

Decimal to Implied Probability

To convert decimal odds into implied probability:

Implied Probability = (1 / Decimal Odds) × 100

For decimal odds of 2.50:

(1 / 2.50) × 100 = 40%

Implied Probability to Decimal

The calculation also works in the opposite direction:

Decimal Odds = 100 / Implied Probability

For an implied probability of 25%:

100 / 25 = 4.00

So a 25% implied probability corresponds to decimal odds of 4.00.

Implied Probability and Bookmaker Margin

Implied probability shows the probability represented by the quoted odds. However, it should not be treated as the exact or true chance of an event happening.

Bookmaker odds can include a margin, which affects probabilities calculated directly from those odds. Research published in the International Journal of Forecasting has examined different methods of converting bookmaker odds into probability estimates and adjusting for this margin. Simply converting odds into percentages therefore does not automatically produce fair or true probabilities.

For example, imagine a simple two-outcome market where both selections are priced at 1.91.

Each price has an implied probability of:

(1 / 1.91) × 100 = 52.36%

For both outcomes together:

52.36% + 52.36% = 104.72%

In a two-outcome market, the underlying probabilities would normally total 100%. The extra 4.72 percentage points in this example represent the bookmaker’s overround before any further adjustment.

A theoretical analysis published in The Journal of Prediction Markets also explains how bookmaker margins relate to the implied probabilities represented by offered odds.

Our Odds Converter calculates implied probability directly from the odds you enter. It does not remove the bookmaker margin, calculate fair odds, or estimate the true probability of an outcome.

Accuracy, Rounding and Calculator Limitations

Different odds formats do not always use the same level of precision, so some converted values need to be rounded for display.

The calculator shows:

• Decimal odds to two decimal places.
• Implied probability to two decimal places.
• American odds as whole numbers with a positive or negative sign.

American odds can occasionally produce an exact value that falls halfway between two whole numbers. The calculator uses JavaScript’s standard rounding method. For negative values ending exactly in .5, this means rounding toward the higher number. For example, an exact American value of -137.5 is displayed as -137. Some conversion tables may instead show -138 because they use a different rounding convention. This one-point difference does not change the underlying decimal odds, implied probability, or potential return.

Fractional odds require slightly different handling. When decimal odds are converted into fractional odds, the calculator looks for a simple fraction that produces the same decimal price when rounded to two decimal places.

For example, decimal odds of 1.83 can be displayed as 5/6:

5 / 6 = 0.8333…

Adding the returned stake gives decimal odds of:

1 + 0.8333… = 1.8333…

which rounds to 1.83.

Because different formats use different levels of precision, converting odds into another format and then converting them back can sometimes produce a small difference. These round-trip differences are usually caused by display precision or rounding conventions rather than a conversion error.

The calculator also checks inputs before performing a conversion. For example:

• Decimal odds must be greater than 1.00.
• American odds must be -100 or lower, or +100 or higher.
• Implied probability must be above 0% and below 100%.
• Fractional odds must use whole positive numbers.
• The denominator in fractional odds cannot be zero.

The calculator is not designed to:

• estimate the true probability of an outcome;
• remove bookmaker margin or calculate fair odds;
• calculate expected value or betting value;
• predict results or recommend bets;
• account for bookmaker-specific settlement rules, commissions, or taxes.

All results are based only on the values entered into the calculator.

Common Fractional Odds Conversion Table

The table below provides a quick reference for common Fractional odds and their Decimal and American equivalents. Decimal values are shown to two decimal places, while American values are rounded to whole numbers. Because different sources may use slightly different rounding conventions, some American conversions can differ by one point.