How to Read Betting Odds: American, Decimal & Fractional

The Three Odds Formats

Sportsbooks around the world use three different formats to display the same information. Understanding all three, and how to convert between them, is fundamental to sports betting.

All three formats express the same thing: the ratio of profit to stake and the implied probability of an outcome.

American Odds (Moneyline)

American odds use a positive or negative number relative to $100.

Negative Odds (Favorites)

A negative number tells you how much you need to bet to win $100.

• -150 means you bet $150 to win $100 profit (total return: $250)
• -300 means you bet $300 to win $100 profit (total return: $400)
• -110 means you bet $110 to win $100 profit (total return: $210)

The larger the negative number, the heavier the favorite.

Positive Odds (Underdogs)

A positive number tells you how much you win on a $100 bet.

• +200 means you win $200 profit on a $100 bet (total return: $300)
• +150 means you win $150 profit on a $100 bet (total return: $250)
• +500 means you win $500 profit on a $100 bet (total return: $600)

The larger the positive number, the bigger the underdog.

Calculating Payout from American Odds

For negative odds:

Payout = Stake x (100 / |Odds|) + Stake

Example: $50 bet at -150 → $50 x (100/150) + $50 = $83.33

For positive odds:

Payout = Stake x (Odds / 100) + Stake

Example: $50 bet at +200 → $50 x (200/100) + $50 = $150

Decimal Odds

Decimal odds show your total return per dollar wagered (including your stake).

• 1.50 means $1 bet returns $1.50 total ($0.50 profit)
• 2.00 means $1 bet returns $2.00 total ($1.00 profit, which is even money)
• 3.50 means $1 bet returns $3.50 total ($2.50 profit)

Why Decimal Is the Simplest Format

The payout calculation is just multiplication:

Total Return = Stake x Decimal Odds
Profit = Stake x (Decimal Odds - 1)

Example: $75 bet at 2.40 → Total return = $75 x 2.40 = $180. Profit = $105.

Decimal odds also make it easy to compare value across markets. The higher the decimal odds, the bigger the payout, with no mental gymnastics with negative signs.

Fractional Odds

Fractional odds show the ratio of profit to stake.

• 2/1 (two-to-one) means $2 profit per $1 staked
• 1/2 (one-to-two) means $1 profit per $2 staked
• 5/4 (five-to-four) means $5 profit per $4 staked

Calculating Payout from Fractional Odds

Profit = Stake x (Numerator / Denominator)
Total Return = Profit + Stake

Example: $40 bet at 5/2 → Profit = $40 x (5/2) = $100. Total return = $140.

Fractional odds are most common in UK horse racing and traditional British sportsbooks. For sports betting analysis, decimal or American are more practical.

Converting Between Formats

American to Decimal

For negative American:

Decimal = 1 + (100 / |American|)

Example: -150 → 1 + (100/150) = 1.667

For positive American:

Decimal = 1 + (American / 100)

Example: +200 → 1 + (200/100) = 3.00

Decimal to American

If decimal < 2.00 (favorite):

American = -100 / (Decimal - 1)

Example: 1.50 → -100 / (1.50 - 1) = -200

If decimal >= 2.00 (underdog or even):

American = (Decimal - 1) x 100

Example: 3.00 → (3.00 - 1) x 100 = +200

Quick Reference Table

Implied Probability

Every set of odds implies a probability of the outcome occurring. This is the most important concept for identifying value.

From Decimal Odds

Implied Probability = 1 / Decimal Odds

Example: 2.50 → 1 / 2.50 = 40%

From American Odds

Negative:

Implied Probability = |American| / (|American| + 100)

Example: -150 → 150 / 250 = 60%

Positive:

Implied Probability = 100 / (American + 100)

Example: +200 → 100 / 300 = 33.3%

Why Implied Probability Matters

Implied probability tells you what the sportsbook thinks the chance of an outcome is (including their margin). If you believe the true probability is higher than what the odds imply, you've found a value bet.

For example, if a team is priced at +200 (implied 33.3%) but you calculate their true probability is 40%, the odds are in your favor. That's a +EV bet.

To get the true probability without the bookmaker's margin, you need to remove the vig.

Common Odds Scenarios

Even Money

• American: +100
• Decimal: 2.00
• Fractional: 1/1 (also called "evens")
• Implied: 50%

A $100 bet returns $200 (your $100 stake + $100 profit).

Heavy Favorite

• American: -300
• Decimal: 1.33
• Fractional: 1/3
• Implied: 75%

You need to risk $300 to win $100. The market thinks this outcome happens 3 out of 4 times.

Big Underdog

• American: +500
• Decimal: 6.00
• Fractional: 5/1
• Implied: 16.7%

A $100 bet returns $600. The market thinks this outcome happens about 1 in 6 times.

Key Takeaways

• American odds show profit relative to $100, with negative for favorites and positive for underdogs
• Decimal odds show total return per dollar and are the simplest format for calculations
• Fractional odds show profit-to-stake ratio and are mostly used in UK markets
• Implied probability is the most important concept because it reveals what the odds actually mean
• All three formats are equivalent. Use whichever you're comfortable with, but understand all of them
• Use an odds converter if you need to switch between formats quickly