Sports Betting Odds Converter: American, Decimal, and Fractional

American Moneyline Odds: The US Format

American odds display as a positive or negative number relative to $100:

Negative odds (favorites) show how much you must risk to win $100. -110 means risk $110 to profit $100. -200 means risk $200 to profit $100. The bigger the negative number, the bigger the favorite.

Positive odds (underdogs) show how much you profit on a $100 bet. +150 means risk $100 to profit $150. +300 means risk $100 to profit $300.

For any bet size (not just $100):

• Negative odds profit = stake × (100 ÷ |odds|). Example: $75 at -130 → 75 × (100/130) = $57.69 profit
• Positive odds profit = stake × (odds ÷ 100). Example: $75 at +175 → 75 × (175/100) = $131.25 profit

Important: "even money" in American odds is either -100 or +100 — both mean equal profit to stake. In practice, books rarely offer exactly even money because of the vig; the standard single-game even-money line appears as -110 on both sides of a spread or total.

American to Decimal Conversion

Decimal odds are the simplest format mathematically. They represent the total return per unit staked, including your original stake. A 2.50 decimal line means $2.50 returned per $1 bet = $1.50 profit per $1 staked.

Positive American → Decimal: (odds ÷ 100) + 1

• +100 → (100/100)+1 = 2.00
• +150 → (150/100)+1 = 2.50
• +200 → (200/100)+1 = 3.00
• +300 → (300/100)+1 = 4.00
• +500 → (500/100)+1 = 6.00

Negative American → Decimal: (100 ÷ |odds|) + 1

• -100 → (100/100)+1 = 2.00 (same as +100 — even money)
• -110 → (100/110)+1 = 1.909
• -120 → (100/120)+1 = 1.833
• -150 → (100/150)+1 = 1.667
• -200 → (100/200)+1 = 1.500
• -400 → (100/400)+1 = 1.250

Decimal odds are easiest for comparing prices across books — higher decimal always means better odds for the bettor on that side. A line at 1.95 decimal is better than 1.909 for a bet on that team, regardless of which American format they translate to.

Decimal to American Conversion

Going back from decimal to American requires two different formulas depending on whether the decimal is above or below 2.00:

Decimal ≥ 2.00 (underdog territory) → Positive American: (decimal − 1) × 100

• 2.00 → (2.00−1)×100 = +100
• 2.50 → (2.50−1)×100 = +150
• 3.00 → (3.00−1)×100 = +200
• 4.50 → (4.50−1)×100 = +350
• 6.00 → (6.00−1)×100 = +500

Decimal < 2.00 (favorite territory) → Negative American: −10 ÷ (decimal − 1)

• 1.909 → −10/(1.909−1) = −10/0.909 = −110
• 1.833 → −10/0.833 = −120
• 1.667 → −10/0.667 = −150
• 1.500 → −10/0.500 = −200
• 1.250 → −10/0.250 = −400

The decimal 2.00 breakpoint is the even-money line. Any decimal above 2.00 is underdog (positive American); any below 2.00 is favorite (negative American). A decimal of exactly 1.00 would mean no profit at all — real sportsbook odds are always above 1.00.

Fractional Odds: The British Format

Fractional odds show profit as a ratio to stake. The numerator is profit; the denominator is the stake needed to earn that profit.

• 5/2 = win 5 units for every 2 units staked = $2.50 profit per $1 bet
• 1/1 (evens) = win 1 unit for every 1 unit staked = even money
• 4/1 = win 4 units per 1 staked = +400 American
• 2/5 = win 2 units for every 5 staked = -250 American (odds-on favorite)

Fractional → Decimal: (numerator ÷ denominator) + 1

• 1/1 → (1/1)+1 = 2.00
• 5/2 → (5/2)+1 = 3.50
• 7/4 → (7/4)+1 = 2.75
• 2/5 → (2/5)+1 = 1.40
• 11/10 → (11/10)+1 = 2.10

Fractional → American: Convert to decimal first, then use the decimal-to-American formula above. 5/2 → 3.50 decimal → (3.50−1)×100 = +250. 2/5 → 1.40 decimal → −10/(1.40−1) = −10/0.40 = −250.

Odds-on favorites in fractional format always have the denominator larger than the numerator (e.g., 2/5, 1/4, 1/10). Reading them: 1/10 means you profit $1 for every $10 bet — a very heavy favorite.

Complete Odds Conversion Reference Table

25 common lines converted across all three formats with implied probability:

• +100 = 2.00 decimal = 1/1 = 50.0% implied
• -110 = 1.909 = 10/11 = 52.4%
• +110 = 2.10 = 11/10 = 47.6%
• -120 = 1.833 = 5/6 = 54.5%
• +120 = 2.20 = 6/5 = 45.5%
• -130 = 1.769 = 10/13 = 56.5%
• +130 = 2.30 = 13/10 = 43.5%
• -140 = 1.714 = 5/7 = 58.3%
• +140 = 2.40 = 7/5 = 41.7%
• -150 = 1.667 = 2/3 = 60.0%
• +150 = 2.50 = 3/2 = 40.0%
• -170 = 1.588 = 10/17 = 63.0%
• +170 = 2.70 = 17/10 = 37.0%
• -200 = 1.500 = 1/2 = 66.7%
• +200 = 3.00 = 2/1 = 33.3%
• -250 = 1.400 = 2/5 = 71.4%
• +250 = 3.50 = 5/2 = 28.6%
• -300 = 1.333 = 1/3 = 75.0%
• +300 = 4.00 = 3/1 = 25.0%
• -400 = 1.250 = 1/4 = 80.0%
• +400 = 5.00 = 4/1 = 20.0%
• -500 = 1.200 = 1/5 = 83.3%
• +500 = 6.00 = 5/1 = 16.7%
• +750 = 8.50 = 15/2 = 11.8%
• +1000 = 11.00 = 10/1 = 9.1%

Implied Probability and Removing the Vig

Every set of betting odds contains an implied probability — the win probability the odds imply.

From decimal odds: implied probability = 1 ÷ decimal odds. 2.50 → 1/2.50 = 40%. 1.909 → 1/1.909 = 52.4%.

The vig problem: A standard -110/-110 spread market has both sides at 52.4% implied probability, totaling 104.8%. A real market can only total 100% — the extra 4.8% is the sportsbook's margin. This is where the house makes money: they collect the vig from losing bettors that exceeds what they pay winning bettors.

Removing the vig (no-vig probability): Divide each side's implied probability by the total of both sides. Example: -110/-110 market. Each side: 52.4%. Total: 104.8%. No-vig probability: 52.4 ÷ 104.8 = 50.0% for each side. The vig-free market says it's genuinely a coin flip.

Another example: -130/+110 market. -130 implied: 130/230 = 56.52%. +110 implied: 100/210 = 47.62%. Total: 104.14%. No-vig: 56.52/104.14 = 54.3% for the favorite, 47.62/104.14 = 45.7% for the underdog. The sportsbook's true estimate of the favorite winning is 54.3%, not 56.5%.

Understanding no-vig probability helps you evaluate whether your own probability estimate beats the book's estimate. If you think the favorite wins 58% of the time vs the book's 54.3% estimate, you have a 3.7-percentage-point edge — that's a positive EV bet at -130.

Practical Application: Comparing Lines Across Books

The real-world value of odds conversion is finding the best available price before betting. Sportsbooks may display different formats, but once converted, comparison is straightforward.

Example: you want to bet on Team A to win. You check five books:

• DraftKings: +148 American = 2.48 decimal = $1.48 profit per $1
• FanDuel: +152 American = 2.52 decimal = $1.52 profit per $1
• Caesars: +155 American = 2.55 decimal = $1.55 profit per $1
• BetMGM: 3/2 fractional = 2.50 decimal = $1.50 profit per $1
• ESPN BET: 1.50 decimal = -200 American = $0.50 profit per $1 (this book has Team A as the favorite, very different read)

Caesars at +155 (2.55 decimal) is the best price for a bet on Team A among the first four books. The ESPN BET line at 1.50 represents a completely different market read — Team A is heavily favored there — suggesting a significant line discrepancy worth investigating.

On a $100 bet: +148 yields $148 profit, +155 yields $155 profit. That $7 difference per $100 staked adds up to $700 over 100 bets of the same size. Line shopping at no additional risk to yourself — the only cost is the time to set up accounts.

Always convert to the same format (decimal is recommended for ease of comparison) before deciding which book to use for any given bet.

Frequently Asked Questions

How do I convert American odds to decimal?

Positive American: (odds ÷ 100) + 1. +150 → 2.50. Negative American: (100 ÷ |odds|) + 1. -110 → 1.909. Decimal odds always represent total return per unit staked including the original stake back.

What is -110 in decimal odds?

-110 American = 1.909 decimal. For a $110 bet, you receive $210.90 back if you win ($110 stake returned + $100 profit). The implied probability of -110 is 52.38%.

How do I calculate implied probability from betting odds?

From decimal: 1 ÷ decimal. From positive American: 100 ÷ (odds + 100). From negative American: |odds| ÷ (|odds| + 100). Both sides of a market will sum above 100% by the vig amount — typically 4–6% for standard markets.

What is the difference between fractional and decimal odds?

Fractional (e.g., 5/2) shows profit relative to stake — win 5 units for every 2 bet. Decimal (e.g., 3.50) shows total return per unit including stake back. Decimal = (numerator/denominator) + 1. 5/2 = 3.50 decimal. Decimal is simpler for comparing prices across books.

How do I convert decimal odds to American odds?

For decimal ≥ 2.00: (decimal − 1) × 100 = positive American. 3.50 → +250. For decimal < 2.00: −10 ÷ (decimal − 1) = negative American. 1.667 → −150. A decimal of exactly 2.00 = +100 (even money).