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American Odds Conversion & Bet Converter: A Complete Guide

American Odds Conversion & Bet Converter: A Complete Guide

Chris Tacker

Written by Chris Tacker
Updated September 27, 2025
3 min to read

At first glance, American odds can look intimidating. Seeing +145 or −120 doesn’t immediately tell you the implied probability or the expected payout. That is why understanding American odds conversion is essential for anyone who takes betting seriously. With the help of a bet converter, you can translate odds into decimal and fractional formats, calculate probabilities, and understand exactly how much you stand to win. BetRocket offers an integrated calculator that does this instantly — but before using the tool, it’s worth understanding the math behind it.

Understanding American odds

American odds are based on a $100 reference point. Positive odds show how much profit you would make from a $100 bet, while negative odds show how much you need to stake in order to win $100.

  • Example: +150 → a $100 bet returns $250 total ($150 profit + $100 stake).
  • Example: −120 → you must bet $120 to make $100 profit.

This format works well for quick profit intuition, but it is less useful when comparing markets across different sportsbooks or evaluating expected value. That’s where conversion comes in.

Converting to decimal odds

Decimal odds show the total return per unit staked, and they are the most common format worldwide.

For positive American odds (+A):

Decimal=1+A100\text{Decimal} = 1 + \frac{A}{100}

For negative American odds (−A):

Decimal=1+100∣A∣\text{Decimal} = 1 + \frac{100}{|A|}

So:

  • +150 → 1+150/100=2.50
  • −120 → 1+100/120≈1.83

Converting to fractional odds

Fractional odds represent profit relative to stake.

For positive odds (+A):

Fractional=A100\text{Fractional} = \frac{A}{100}

For negative odds (−A):

Fractional=100∣A∣\text{Fractional} = \frac{100}{|A|}

Thus, +150 becomes 3/2, while −120 converts to roughly 5/6.

Calculating implied probability

The most valuable part of conversion is seeing the true probability implied by the odds.

For positive odds (+A):

p=100A+100p = \frac{100}{A + 100}

For negative odds (−A):

p=∣A∣∣A∣+100p = \frac{|A|}{|A| + 100}

Examples:

  • +150 → 100/(150+100)=0.40 → 40% chance
  • −120 → 120/(120+100)≈0.545 → 54.5% chance

Reverse conversion: from probability to American odds

Sometimes you want to go the other way — starting with a probability (from a model, for example) and finding the equivalent American price.

If probability is less than 50% (underdog):

Odds=+100(1−p)p\text{Odds} = +\frac{100(1 - p)}{p}

If probability is 50% or higher (favorite):

Odds=−100p1−p\text{Odds} = -\frac{100p}{1 - p}

So, if your model gives a 40% win chance, the fair line is +150. If the chance is 55%, the fair line is about −122.

Why a bet converter is essential

While the math isn’t complicated, applying it quickly across multiple markets or in-play situations is difficult. A bet converter automates the process: you input American odds and a stake, and it shows the decimal and fractional equivalents, the implied probability, and the expected profit. For parlays, the converter multiplies decimal odds of each leg to give you combined probability and return.

This is especially important when comparing lines across different sportsbooks or between a sportsbook and an exchange. Even a small difference in implied probability can make the difference between a losing strategy and a profitable one.

How BetRocket makes it easier

BetRocket integrates a professional-grade Odds Converter. It does all the heavy lifting instantly: American to decimal, fractional, and probability — as well as reverse conversion from probability to odds. 

Conclusion

American odds conversion may look confusing at first, but the formulas are straightforward once you know them. By converting odds to decimal or fractional and calculating implied probabilities, you can evaluate markets more accurately and make smarter betting decisions. A bet converter saves time and eliminates errors, and with BetRocket’s integrated tool, you can go from raw numbers to actionable insights in seconds.