3 Mar

Calculating Win/Loss % from Implied Odds

How to Convert Implied Odds into Win Probability

How to Convert Implied Odds into Win ProbabilitySports bettors who rely on a betting strategy often utilize the implied odds of a sportsbook to determine the expected value and correct bet size for their wagers. The Kelly Criterion System is a perfect example. The scientific gambling formula requires the bettor to inject a range of variables, including the probability of winning the bet, and the probability of losing it.

Unless you’re a die-hard sports fan with immaculate (borderline psychic) knowledge of a sport, worthy of professional sharp rating, chances are your win/loss probability predictions aren’t all that accurate. More like guess-timates, at best. That’s why most serious sports bettors utilize the opening lines of an event to pin-point these figures. They aren’t guaranteed accurate, but they are set by professional oddsmakers, and are as close as you’re going to get to consistent accuracy.

Understanding Implied Odds in Sports Betting

Implied odds are the measure of probability that something will or will not happen. We know a toss of a coin has a probability of 50% for landing on heads, and 50% on tails. In poker, probabilities have to do with the exact number of cards available, compared to the number of cards that will give you the desired result. Sports betting is entirely different.

In sports, probabilities are rarely equal, nor are they precise. One side’s propensity to win is determined by the performance of the team as a complete unit, as well as the individual skill of each athlete. A multitude of factors can impact the odds; everything from the common cold to rainy weather.

That being said, implied odds in sports betting are, quite simply, the probability of something happening, as implied by the great and wise oddsmakers. When we convert the implied odds into a percentage, they become the supposed win probability for that team.

Converting Implied Odds into Win Probability

There’s a very simple formula for figuring out the win probability based on the odds presented by a sportsbook. However, there are three different ways those odds could be displayed – US moneyline odds, EU decimal odds, or UK fractional odds. We’ll go over the formula for each one, but first…

I stated above that “serious sports bettors utilize the opening lines” to determine probability. It is crucial that you only use the opening lines – that is, the original lines set by the book when an event is first posted for wagering on. Once the lines shift, you’re dealing with new odds designed to benefit the bookmaker, based not on actual probabilities, but rather the betting tendencies of those wagering on the event. Alternate lines are designed to balance the books (i.e. ensure a profit for the bookie). Only the opening lines are based on the genuine probability of each outcome occurring, and even that information is subject to the opinion of the most esteemed handicappers (the oddsmakers) and computer algorithms.

That being said, I’ll now show you how to calculate the win and loss % from each regional odds format, based on the following mock lines. We’ll assume that the NFL’s San Francisco 49ers are playing the Tampa Bay Buccaneers this Sunday, and the sportsbook is posting its opening lines as follows.

US Odds
EU Odds
UK Odds
Tampa Bay Buccaneers
San Francisco 49ers

We can immediately assume from the information above that Tampa Bay is the favorite, and San Francisco the underdog. But just how probable is it that Tampa will win?

US Odds to Win %

US odds, or moneylines, are represented by a positive or negative integer. In the example, we see US odds of -300 Tampa Bay, +250 San Francisco. The formula for converting these odds to win/loss probability varies by whether the line is positive or negative.

When the line is positive, the formula is: 100 / (Odds + 100) * 100 = Win%

  • 49ers: 100 / (275 + 100) * 100 = 26.66%

If the line is negative, the formula is: Odds / (Odds+100) * 100 = Win%

  • Bucs: 300 / (300 + 100) * 100 = 75%

EU Odds to Win %

EU odds are represented as a decimal; in this case 1.33 for Tampa Bay, and 3.75 for San Francisco.

The formula for calculation is: (1 / Odds) * 100 = Win%

  • 49ers: (1 / 3.75) * 100 = 26.66%

  • Bucs: (1 / 1.33) * 100 = 75.19%

UK Odds to Win %

UK odds are listed as fractional integers; in this case 1/3 for Tamps Bay, 11/4 for San Francisco.

The formula for win probability is: Denominator / (Denominator + Numerator) * 100 = Win%

    • 49ers: 4 / (4 + 11) * 100 = 26.66%

    • Bucs: 3 / (3 + 1) * 100 = 75%

Evaluating the Data

One major point of interest – I’m sure you noticed it already – is that the implied win probability for both teams does not equal 100%. That’s because sportsbooks set the lines so that, with balanced betting on both sides, they are guaranteed to make a profit. The difference in the probabilities (1.66%) is the amount of money the sportsbook intends to scoop off the top as its profit. When the bets aren’t coming in balanced, that’s when the sportsbook shifts the lines, encouraging bets on the other side to “balance the books”. And, that’s exactly why the opening lines are the most accurate choice for calculating win probability from implied odds.

So, from this data, we can assume that the Tampa Bay Buccaneers are favored with about a 75% chance to win, and 25% chance to lose. If you’re looking to bet on the 49ers, they have a 26.66% chance to win, and a 73.33% chance to lose. Again, no, they aren’t even, but if you’re injecting win/loss probabilities into the formula of your scientific gambling method, these are the numbers you’ll be collecting from the data.

Win Probability vs. Loss Probability

The Win Probability is the solution to the formula (above). The Loss Probability is the difference, calculated as: 100 – Win Probability = Loss Probability.

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