ConverterHub

Probability to Odds Converter

Odds against and decimal odds for any probability between 0 and 100%.

How it is calculated

You enter the probability as a percentage, strictly between 0 and 100. The tool turns it into a fraction p = P ÷ 100 and gives two numbers: odds against (1 − p) ÷ p, shown as x : 1, and decimal odds 1 ÷ p. Decimal odds include your stake: they are the total return per 1 unit staked, so decimal odds = odds against + 1. Both are rounded to two decimals, so a repeating value like 1.6667 appears as 1.67. Values of 0 or less and values of 100 or more give no result, since the odds would be infinite or zero. The tool shows fair odds, with no bookmaker margin included.

Worked example

Suppose you judge an outcome to have a 37.5% chance. Then p = 0.375. Odds against: (1 − 0.375) ÷ 0.375 = 0.625 ÷ 0.375 = 1.6667, shown as 1.67 : 1. Decimal odds: 1 ÷ 0.375 = 2.6667, shown as 2.67. A bookmaker offering decimal odds above 2.67 on this outcome would be paying more than your fair price, so it would be worth a bet if your estimate is right.

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Common mistakes

  • Entering the probability as a fraction (0.375) instead of a percentage (37.5); the tool would read it as 0.375% and give odds of 265.67 : 1.
  • Confusing odds against (x : 1, stake not included) with decimal odds (stake included); they differ by exactly 1.
  • Expecting a bookmaker's quoted price to match: real odds include a margin, so quoted prices are shorter than the fair odds this tool gives.
  • Reading 1.67 : 1 as 1.67 to 1 for the event happening; it is odds against, so it favours the outcome not happening.
  • Entering 0 or 100 for a certain or impossible event, where odds cannot be defined.

About this calculator

Converting a probability into betting odds uses the relationship odds against = (1 − p) / p, expressed as a ratio such as "3 to 1". A probability of 25% (p = 0.25) becomes odds against of (0.75/0.25) = 3, written 3-to-1, while a coin flip's 50% probability becomes even odds, 1-to-1. The reverse direction, odds to probability, is p = 1 / (odds + 1) when odds are expressed as "n to 1" against.

Bookmakers and oddsmakers price markets in odds rather than raw probabilities because odds directly determine payouts, while bettors and analysts often prefer probabilities to compare an implied chance against their own estimate of the true likelihood, spotting value bets where the market's implied probability looks too low.

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