Master Odds Converter
Seamlessly translate between international odds formats and reveal the implied market probability. Seamlessly convert between Decimal, American, and Fractional formats with instant implied probability calculation.
Understanding odds formats is crucial for cross-market arbitrage and identifying value. Decimal odds represent the total return (stake + profit). American odds show either how much you need to bet to win $100 (negative) or how much $100 wins (positive).
The most important metric for a bettor. It converts odds into a percentage chance of an event occurring:1 / Decimal Odds = Probability. If your estimate is higher than this, you've found "Value".
How the Odds Converter Works
Betting odds exist in three formats: Decimal (Europe/Australia), American/Moneyline (USA), and Fractional (UK/Ireland). All three express the same underlying probability β they simply present it differently. A professional bettor must be fluent in all three because the same event may be quoted in different formats across different bookmakers.
Decimal odds are the simplest to work with mathematically. A decimal odd of 2.50 means you receive $2.50 for every $1 wagered β your original stake plus $1.50 profit. The implied probability is simply 1 / decimal odds. Decimal odds of 1.50 β 66.67% implied probability. Any decimal below 2.00 means the bookmaker considers the outcome more likely than not.
American odds work differently for favorites and underdogs. Negative values (e.g., β150) show how much you must bet to win $100. Positive values (e.g., +130) show how much $100 wins you. Converting: positive American β decimal = (American / 100) + 1; negative American β decimal = (100 / |American|) + 1. A β150 line equals decimal 1.667, equivalent to fractional 2/3.
Fractional odds (e.g., 5/2, pronounced "five-to-two") express net profit relative to stake. 5/2 means you profit $5 for every $2 staked, for a total return of $7. To convert to decimal: (numerator / denominator) + 1. The implied probability is the denominator divided by (numerator + denominator): 2/(5+2) = 28.57%.
Conversion Formulas
Implied Probability = 1 / Decimal
Decimal from American = (Amer / 100) + 1 [if Amer > 0]
= (100 / |Amer|) + 1 [if Amer < 0]
Decimal from Fraction = (Num / Den) + 1
American from Decimal = (Dec β 1) Γ 100 [if Dec β₯ 2.00]
= β100 / (Dec β 1) [if Dec < 2.00]Conversion Examples
Decimal: 2.00 = American +100 = Fractional 1/1. Implied: 50.00%.
Decimal: 1.25 = American β400 = Fractional 1/4. Implied: 80.00%.
Decimal: 5.00 = American +400 = Fractional 4/1. Implied: 20.00%.
Frequently Asked Questions
Which odds format should I use for calculations?
Decimal odds are best for mathematical calculations β implied probability, expected value, and Kelly Criterion all use decimal format as their base. Use this converter to translate bookmaker quotes into decimal, then apply your formulas.
Why do bookmakers quote different formats?
It's purely regional convention. European and Australian books use decimal. UK and Irish books traditionally use fractional. North American books use moneyline. Most online bookmakers let you switch formats in account settings.
What is implied probability and why does it matter?
Implied probability is the win percentage the bookmaker's odds suggest. If implied probability is 45% but you estimate the true probability at 52%, you have a 7% edge. Recognizing this discrepancy is the entire foundation of professional betting.
Why does the sum of implied probabilities exceed 100%?
Because bookmakers add a margin (vig/overround) across all outcomes. A standard market with 1.91/1.91 odds has 52.36% + 52.36% = 104.72% total. The excess 4.72% is the bookmaker's profit margin built into the odds.