Sports Betting Odds Converter

Sports betting odds are displayed differently around the world. Americans see +150, Europeans see 2.50, and the British see 3/2. This tool converts between all three formats instantly and reveals the implied probability behind any odds.

Universal Odds Converter

Enter odds in any format and see instant conversions plus implied probability

Select Input Format:

+

Positive (+) = underdog, Negative (-) = favorite. Enter without the +/- sign.

Implied Probability
40.00%
Win Chance

These odds suggest a 40% chance of winning. The remaining 60% represents the implied chance of losing.

All Formats

🇺🇸
American
+150
Moneyline
🇪🇺
Decimal
2.50
European
🇬🇧
Fractional
3/2
British

💰 Calculate Your Payout

Potential Profit
$150.00
Total Return
$250.00
Break-Even %
40.00%

Quick Reference: Common Odds

Understanding Odds Formats

Betting odds serve two purposes: they indicate how much you can win and they reveal the implied probability of an outcome. Different regions developed their own conventions, but they all express the same mathematical relationship between risk and reward.

According to the American Gaming Association, sports betting is now legal in over 35 U.S. states, making understanding American odds increasingly important for bettors worldwide. Meanwhile, European sportsbooks continue using decimal odds, and British bookmakers maintain their traditional fractional format.

🇺🇸

American (Moneyline) Odds

Based on a $100 wager. Positive odds (+150) show how much profit you'd win on a $100 bet. Negative odds (-150) show how much you must bet to win $100 profit. The favorite has negative odds; the underdog has positive odds.

🇪🇺

Decimal (European) Odds

The simplest format: multiply your stake by the decimal to get your total return (including stake). Odds of 2.50 mean a $100 bet returns $250 total ($150 profit + $100 stake). Always greater than 1.00.

🇬🇧

Fractional (British) Odds

Shows profit relative to stake. Odds of 3/2 mean you win $3 for every $2 wagered (plus your stake back). Read as "three to two." Also written as 3-2 or spoken as "three-to-two."

The Mathematics of Conversion

Converting between formats requires understanding the relationship between odds and probability. The Encyclopaedia Britannica defines probability as the likelihood of an event occurring, expressed as a number between 0 and 1 (or 0% to 100%).

American to Decimal Conversion

If American odds are POSITIVE (+150):
Decimal = (American / 100) + 1
Example: (+150 / 100) + 1 = 2.50

If American odds are NEGATIVE (-150):
Decimal = (100 / |American|) + 1
Example: (100 / 150) + 1 = 1.667

Decimal to American Conversion

If Decimal >= 2.00:
American = (Decimal - 1) × 100
Example: (2.50 - 1) × 100 = +150

If Decimal < 2.00:
American = -100 / (Decimal - 1)
Example: -100 / (1.667 - 1) = -150

Implied Probability Formula

From Decimal odds:
Implied Probability = (1 / Decimal) × 100%
Example: (1 / 2.50) × 100 = 40%

From American odds (+):
Implied Probability = 100 / (American + 100) × 100%
Example: 100 / (150 + 100) = 40%
Why Implied Probabilities Don't Add to 100%: When you add up the implied probabilities for all outcomes in a bet (like both sides of a game), the total exceeds 100%. This "overround" or "vigorish" (vig) is how bookmakers guarantee profit. A typical -110/-110 line has about 4.5% overround. The UNLV International Gaming Institute documents this as the fundamental business model of sports betting.

Odds Comparison Table

This reference table shows equivalent odds across all three formats, plus the implied probability:

American Decimal Fractional Implied Probability
-500 1.20 1/5 83.33%
-300 1.33 1/3 75.00%
-200 1.50 1/2 66.67%
-150 1.67 2/3 60.00%
-110 1.91 10/11 52.38%
+100 2.00 1/1 50.00%
+110 2.10 11/10 47.62%
+150 2.50 3/2 40.00%
+200 3.00 2/1 33.33%
+300 4.00 3/1 25.00%
+500 6.00 5/1 16.67%
+1000 11.00 10/1 9.09%

The Standard Vig: Why -110 Is Everywhere

In American sports betting, the standard line is -110 on both sides. This means you must wager $110 to win $100. If bets are evenly distributed, the bookmaker collects $220 and pays out $210 to the winner—keeping $10 (4.55%) regardless of outcome.

This is the same mathematical principle behind the house edge in casino games—the operator's profit margin built into the odds. Just as casinos pay less than true odds, sportsbooks set lines that guarantee profit through the vigorish.

Did You Know? The term "vigorish" (often shortened to "vig" or "juice") comes from Yiddish slang. It originally referred to interest charged on a loan but evolved to describe the bookmaker's commission built into betting odds. Professional bettors obsess over finding lines with lower vig—even a reduction from -110 to -105 significantly impacts long-term results.

Line Shopping and Odds Comparison

Different sportsbooks offer slightly different odds on the same event. One might offer a team at -105 while another lists them at -115. This difference matters enormously over time. According to research documented by the National Council on Problem Gambling, understanding odds is crucial for informed decision-making—whether choosing to bet or recognizing the mathematical reality of gambling.

A bettor who consistently gets -105 instead of -110 reduces the vig from 4.76% to 2.38%—cutting the built-in disadvantage in half. This is why the MIT Blackjack Team's advantage play principles apply to sports betting too: finding edges in the math.

Practical Applications

Converting On-the-Fly

Quick mental shortcuts for common conversions:

  • +100 = 2.00 decimal = evens (1/1) — The baseline "coin flip" odds
  • -110 ≈ 1.91 decimal ≈ 10/11 — Standard American sportsbook line
  • +200 = 3.00 decimal = 2/1 — Classic "two-to-one" underdog
  • -200 = 1.50 decimal = 1/2 — Two-to-one favorite ("one-to-two against")

Understanding Value

If you believe a team has a 50% chance of winning but they're listed at +120 (implied probability 45.45%), the odds are offering more than the "true" probability suggests. This is "positive expected value"—though proving you can consistently identify such opportunities is another matter entirely.

This concept mirrors what we explore in our Session Outcome Calculator: understanding expected value is essential, but variance means individual outcomes remain unpredictable.

Key Insight: Odds formats are just different languages describing the same mathematical reality. A +150 underdog, a 2.50 decimal bet, and a 3/2 fractional wager all represent identical risk/reward profiles. Understanding the conversions helps you compare odds across international sportsbooks and identify the best available lines.

The Global Betting Market

Sports betting is increasingly global, with bettors accessing books from multiple jurisdictions. The ability to instantly convert between formats isn't just academic—it's practical for anyone comparing lines across different platforms.

Just as understanding casino design psychology reveals how gambling environments are constructed, understanding odds formats reveals how betting markets present information. Neither knowledge guarantees profit, but both provide valuable perspective on an industry designed to maintain a mathematical edge.

Remember: This tool is for educational purposes—understanding how betting odds work and what they represent mathematically. Knowledge of odds formats won't change the underlying probabilities or guarantee success. If you or someone you know needs support with gambling, the National Problem Gambling Helpline is available 24/7 at 1-800-522-4700.

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