Odds Converter & Probability Calculator
Convert between decimal, fractional, and American odds formats instantly. Calculate implied probability, bookmaker margins, and fair odds across EU betting markets.
Why Understanding Odds Matters
Different EU countries traditionally use different odds formats. UK and Irish bookmakers use fractional odds (e.g., 5/1), while continental Europe typically uses decimal odds (e.g., 6.00). American odds (+500) are common on international platforms. Understanding how to convert between these formats helps you compare offers and calculate your actual probability of winning.
Convert Your Odds
Enter odds in any format and instantly see the equivalent in all other formats, plus the implied probability.
Quick Examples
Click to auto-fill common odds values:
Enter a probability percentage and see what odds would represent that likelihood. Useful for understanding if odds offer value.
Common Probabilities
Enter odds for all outcomes in a market to calculate the bookmaker's overround (margin/vig). Lower overround means better value for bettors.
Enter Odds for All Outcomes
Add all possible outcomes in the market (e.g., Home/Draw/Away for football)
Understanding Betting Odds Formats
Betting odds represent the ratio between your stake and potential winnings, and they also imply the probability of an outcome occurring. Different regions traditionally use different formats, which can make comparing odds across bookmakers challenging without a conversion tool.
Decimal Odds (European Format)
Decimal odds are the most straightforward format, commonly used across continental Europe and increasingly worldwide. The number represents your total return (stake + profit) per unit staked. For example, odds of 2.50 mean you receive €2.50 for every €1 wagered (€1.50 profit + €1 stake back).
According to Britannica's gambling overview, decimal odds have become the standard format for online bookmakers because they're easier to calculate and compare than fractional alternatives.
- Formula: Total Return = Stake × Decimal Odds
- Profit: Profit = Stake × (Decimal Odds - 1)
- Implied Probability: 1 / Decimal Odds × 100
Fractional Odds (British Format)
Fractional odds, traditional in the UK and Ireland, show potential profit relative to stake. Odds of 5/1 ("five to one") mean you win £5 profit for every £1 staked. Fractional odds don't include your stake in the displayed number.
The format can be counterintuitive: 1/5 (called "one to five on" or "5 to 1 on") means you're betting on a strong favorite - you must stake £5 to win £1 profit.
- Formula: Profit = Stake × (Numerator / Denominator)
- Total Return: Stake × (Numerator / Denominator) + Stake
- Implied Probability: Denominator / (Numerator + Denominator) × 100
American Odds (Moneyline)
American odds use a baseline of $100 and display differently for favorites (negative numbers) and underdogs (positive numbers). As explained by Investopedia's guide to betting mathematics, positive odds show how much you win on a $100 stake, while negative odds show how much you must stake to win $100.
- Positive odds (+150): Stake $100 to win $150 profit
- Negative odds (-150): Stake $150 to win $100 profit
- Even money: Displayed as +100 or -100
Implied Probability and Value Betting
Every set of odds implies a probability that the bookmaker believes represents the chance of that outcome occurring (plus their margin). Understanding implied probability is essential for identifying potential value in betting markets.
As documented by the UK Gambling Commission's guide to how gambling works, all gambling operators build a margin into their odds. This means the combined implied probabilities of all outcomes in a market will exceed 100%.
Value Betting Concept
If you believe an outcome has a 50% chance of occurring, but the bookmaker offers odds implying only a 40% chance (decimal 2.50), this represents "value" - the odds are more generous than the true probability warrants. However, accurately assessing true probabilities is extremely difficult, which is why bookmakers consistently profit over time.
What is Overround?
Overround (also called vig, vigorish, or margin) is the bookmaker's built-in profit margin. In a fair market, the implied probabilities of all outcomes would sum to exactly 100%. Bookmakers set odds so this total exceeds 100%, ensuring long-term profit regardless of the outcome.
For example, in a fair coin flip:
- Fair odds: 2.00 for Heads, 2.00 for Tails (100% total implied probability)
- With 5% overround: 1.90 for Heads, 1.90 for Tails (105.3% total implied probability)
Lower overround means better value for bettors. Competitive markets like major football matches typically have overrounds of 2-5%, while niche markets or exotic bets may have overrounds exceeding 10%.
Odds Formats Across EU Countries
Different EU markets have traditionally preferred different odds formats, though decimal odds are increasingly dominant online:
| Country/Region | Traditional Format | Online Standard |
|---|---|---|
| UK & Ireland | Fractional (5/1) | Both options |
| Germany, France, Spain | Decimal (6.00) | Decimal |
| Italy | Decimal | Decimal |
| Netherlands | Decimal | Decimal |
| Nordic Countries | Decimal | Decimal |
For detailed information on gambling regulations in specific EU countries, see our country guides including Germany, Netherlands, and France.
Mathematical Conversions
Understanding the mathematical relationships between odds formats helps verify conversions and deepen understanding of probability:
Converting Between Formats
| From | To Decimal | To Fractional | To American |
|---|---|---|---|
| Decimal | - | (D-1)/1 | If D≥2: (D-1)×100 If D<2: -100/(D-1) |
| Fractional (N/D) | (N/D)+1 | - | If N≥D: N/D×100 If N<D: -100×D/N |
| American | If +: (A/100)+1 If -: (-100/A)+1 |
If +: A/100 If -: 100/|A| |
- |
Practical Applications
Comparing Bookmaker Offers
Different bookmakers may display the same market using different odds formats. Converting all options to the same format (typically decimal) allows direct comparison of value. Our regulation comparison tool can help you understand which licensed operators are available in different EU markets.
Understanding Sports Betting Markets
Sports betting is treated differently from casino gambling in many EU jurisdictions. As explained in our casino vs sports betting comparison, some countries regulate sports betting more liberally than casino games. Understanding odds is fundamental to participating in these markets responsibly.
Responsible Gambling Considerations
Understanding odds and probability is part of informed gambling. Our bankroll management calculator helps you set appropriate limits, while the house edge calculator demonstrates the mathematics underlying casino games. For information on problem gambling support, see our problem gambling resources.
Related Tools & Resources
- Parlay/Accumulator Calculator - Calculate combined odds and probability for multi-bet parlays
- House Edge Calculator - Understand expected value and RTP
- Bankroll Management Calculator - Set responsible gambling limits
- EU Gambling Tax Calculator - Understand operator taxation
- Regulation Comparison Tool - Compare rules across EU countries
- Glossary - Key gambling and regulatory terms explained
⚠ Legal Disclaimer
This tool is for educational and informational purposes only. It demonstrates odds conversion and probability concepts. This is not gambling advice or encouragement to gamble. Gambling always carries risk of loss. If you choose to gamble, do so responsibly and within legal frameworks in your jurisdiction. For help with problem gambling, contact BeGambleAware or Gambling Therapy.
Last Updated: December 2025