Betting Odds Converter

Last updated: 2026-05-25

Four Ways to Write the Same Odds

Odds are expressed differently around the world: decimal format dominates in Europe and Australia, fractional odds are standard in the UK and Ireland, and American moneyline odds are used in North American sports betting. This converter lets you move freely between all four representations — including implied probability — from a single decimal input.

The Four Formats

Decimal odds (e.g. 3.50) represent the total payout per 1 unit staked, including the stake. A $10 bet at 3.50 returns $35 total ($25 profit + $10 stake).

Fractional odds (e.g. 5/2) represent profit relative to stake. 5/2 means $5 profit for every $2 staked.

American odds (moneyline) come in two forms:

Positive (+250): the profit on a $100 stake. A $100 bet at +250 returns $350 total.
Negative (−150): the stake needed to profit $100. You must wager $150 to win $100.

Implied probability is what the odds say the true probability of the outcome is, before the bookmaker's margin is applied.

Conversion Formulas

All conversions derive from decimal odds as the canonical form.

\text{Fractional} = \text{Decimal} - 1

P_{\text{implied}} = \frac{100}{\text{Decimal}} \%

\text{American} = \begin{cases} (\text{Decimal} - 1) \times 100 & \text{if Decimal} \geq 2 \\ \dfrac{-100}{\text{Decimal} - 1} & \text{if Decimal} < 2 \end{cases}

Example: Decimal odds of 3.50:

Fractional: 3.50 − 1 = 5/2
Implied probability: 100 / 3.50 = 28.57%
American: (3.50 − 1) × 100 = +250

Understanding the Bookmaker Margin

The sum of implied probabilities across all outcomes in a market will always exceed 100%. The excess is the bookmaker's margin (or "vig"). For example, a coin-flip market might show each side at 1.91 (implied probability 52.4%), summing to 104.8%. The extra 4.8% is the margin.

Frequently Asked Questions (FAQ)

How do I convert decimal odds to probability?

Divide 100 by the decimal odds. For 3.50: 100 / 3.50 = 28.57%. This is the implied probability the bookmaker assigns to the event.

How do I read American moneyline odds?

Positive (+250): the profit on a $100 bet — you win $250, collecting $350 total. Negative (−150): the amount you must stake to win $100 — you wager $150 to collect $250 total.

What is the difference between decimal and fractional odds?

Decimal includes the stake in the return figure; fractional shows only the profit relative to stake. 3.50 decimal = 5/2 fractional (both mean the same bet, just different conventions).

Which format should I use?

Use whichever format your bookmaker displays. Decimal is easiest to compare quickly — higher decimal = more potential return. For calculating exact payouts, decimal arithmetic is the simplest.

Disclaimer

This tool is for informational purposes only. It converts between odds formats mathematically and does not account for bookmaker margins, exchange commissions, or regional restrictions. Gambling involves financial risk; please gamble responsibly.

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