How to Read Sports Betting Odds

ProphetAiQ Team · 2026-02-05

Sports betting odds are implied probability plus the house margin expressed in American, decimal, or fractional format. Learn to convert between formats, calculate the vig, and compare odds to ProphetAiQ confidence scores to identify value.

Executive summary: Sports betting odds are implied probability plus the house edge. Convert odds to percentages to compare directly to ProphetAiQ confidence scores — if the model says 58% but the market implies 54%, you have a thesis to research.

Quick take

• American: -150 means risk $150 to win $100; +150 means risk $100 to win $150
• Decimal 2.10 × stake = total return (including stake)
• Implied probability = inverse of decimal odds (before vig removal)

Sports betting odds are numerical expressions of implied probability combined with the sportsbook's built-in margin (vig), and understanding how to read and convert between American, decimal, and fractional formats is the prerequisite for every other betting concept including expected value, line shopping, and bankroll management.

What Are Sports Betting Odds?

Sports betting odds are numerical expressions of implied probability combined with the sportsbook's built-in margin, used to calculate both payouts and the market's assessment of how likely an outcome is. Understanding odds is the foundation of every other betting concept — from calculating expected value to line shopping across sportsbooks.

How Do American Odds Work?

American odds are the standard format at U.S. sportsbooks. Negative numbers indicate favorites; positive numbers indicate underdogs.

Implied probability conversions:

• -200 → 200 ÷ 300 = 66.7%
• -110 → 110 ÷ 210 = 52.4%
• +150 → 100 ÷ 250 = 40.0%

What Are Decimal Odds?

Decimal odds show total return per $1 wagered including your stake. Decimal 1.91 ≈ American -110. Decimal 2.50 = American +150.

The conversion: multiply your stake by the decimal number. A $100 bet at 2.50 returns $250 total ($150 profit).

What Is the Vig and How Does It Affect You?

The vig (juice) is the sportsbook's built-in margin. On a standard -110/-110 line, both sides imply 52.4% — totaling 104.8%. The extra 4.8% is the book's guaranteed edge on balanced action.

To find "true" no-vig odds, divide each side's implied probability by the combined total: 52.4 ÷ 104.8 = 50% each. The vig costs you approximately 2.4% per bet at standard juice.

How Do Odds Formats Convert Between Each Other?

Conversion formulas:

• American negative → Decimal: (|odds| + 100) / |odds| → -150 = 250/150 = 1.667
• American positive → Decimal: (odds + 100) / 100 → +150 = 250/100 = 2.50
• Decimal → Implied Prob: 1 / decimal × 100 → 1/2.50 = 40%

What Is the Best Way to Practice Reading Odds?

Open the ProphetAiQ games page and practice converting the displayed odds to implied probability for every game on today's slate. Then compare your implied probability calculation to ProphetAiQ's confidence score — if the model says 62% but the market implies 54%, you have identified a potential value gap worth investigating further.

Do this for one week — 5-10 games per day — and the conversion math becomes automatic. You will start seeing lines not as numbers but as probability statements, which fundamentally changes how you evaluate every potential bet.

How Do You Use Odds to Find Value?

If ProphetAiQ shows 62% confidence on a team and the book prices them at -130 (60.5% implied), the 1.5% gap is your potential edge. Compare the model's confidence to the market's implied probability — when the model sees higher probability than the market, that is a value signal.

Practice on live games at ProphetAiQ — click any game card to see confidence scores alongside market odds.