Odds Converter

Convert between American, Decimal, Fractional, and implied probability formats instantly. See the true probability behind any line.

Presets:

Odds Input

American Odds e.g. +150 or -200

Decimal Odds e.g. 2.50

Fractional Odds e.g. 3/2

Implied Probability

Results

American

+100

Decimal

2.00

Fractional

Evs

Implied Prob.

50.00%

Stake

Break-Even Win Rate

50.00%

Payout on $100 Bet

$200.00

Net Profit on $100 Bet

+$100.00

Odds Type

Even Money

Market Margin (optional)

Side A (above)

+100

Side B (American)

At even money, you need to win more than 50% of the time to be profitable. This is the baseline that separates favorites from underdogs.

Bulk Convert

Paste one odds value per line (or comma-separated). Auto-detects American (+/-), Decimal (>1.01), or Fractional (x/y) format. Max 20 rows.

Enter odds above to see conversions

Understanding Odds Formats

American Odds (Moneyline)

American odds are the standard format used by sportsbooks in the United States. They come in two flavors: positive and negative. A positive number (e.g. +150) tells you how much profit you win on a $100 bet, so +150 means a $100 bet returns $250 total ($150 profit). A negative number (e.g. -200) tells you how much you need to wager to win $100 in profit, so -200 means you must bet $200 to profit $100. The bigger the negative number, the heavier the favorite; the bigger the positive number, the bigger the underdog.

Decimal Odds

Decimal odds are the most popular format worldwide, used throughout Europe, Australia, and Canada. They represent the total payout per $1 wagered, including your original stake. A decimal of 2.50 means a $1 bet returns $2.50 total ($1.50 profit + $1 stake). Converting is simple: just multiply your stake by the decimal. Decimal odds of 2.00 represent an even-money bet (50% implied probability). Anything below 2.00 is a favorite; anything above is an underdog.

Fractional Odds

Fractional odds are the traditional format in the United Kingdom and Ireland, commonly used in horse racing. They show the ratio of profit to stake. For example, 3/2 (read as "three to two") means for every $2 wagered, you profit $3, so a $100 bet at 3/2 returns $250 ($150 profit). Evens (1/1) is the equivalent of +100 American or 2.00 Decimal. When the numerator is smaller than the denominator (e.g. 1/2), the selection is a favorite.

Implied Probability

Implied probability converts any odds format into the percentage chance the bookmaker is pricing in for that outcome to occur. This is the most important number for finding value. If your own analysis says a team has a 60% chance of winning, but the odds imply only 50%, you have found a +EV (positive expected value) opportunity. Keep in mind that sportsbook odds include a margin (vigorish/juice), so the implied probabilities across all outcomes in a market will sum to more than 100%.

Conversion Formulas

Positive American → Decimal = (American / 100) + 1Negative American → Decimal = (100 / |American|) + 1Decimal → Fractional = (Decimal - 1) as fractionImplied Prob = 1 / Decimal × 100%

Mastering all four formats gives you a significant edge when shopping for lines across international sportsbooks. Many sharp bettors compare odds in decimal format for its simplicity, then convert to implied probability to assess value. The ability to quickly translate between formats without relying on a calculator is a skill that separates recreational bettors from professionals.

Understanding Betting Odds Formats

American Odds (+150 / -150)

American odds, also called moneyline odds, are the standard format at US sportsbooks. They come in two flavors built around the number 100. A positive number like +150 tells you the profit on a $100 stake: bet $100, profit $150, collect $250 total. A negative number like -150 tells you how much you must risk to profit $100: bet $150, profit $100, collect $250 total. The key insight is that -110 on both sides of a market is the industry-standard juice. It means you lay $110 to win $100, giving the sportsbook a 4.55% margin. Any line better than -110 for your side means less vig; anything worse means more.

Decimal Odds (2.50 / 1.67)

Decimal odds are the global standard, dominant across Europe, Australia, Canada, and all major betting exchanges (Betfair, Smarkets, Betdaq). They represent the total return per unit staked, including the stake itself. A decimal of 2.50 means $1 wagered returns $2.50 ($1.50 profit + $1 stake). The conversion is immediate: multiply your stake by the decimal to get the total payout. Decimal odds make parlay math trivial: just multiply the decimals together. They also make implied probability a single division: 1 / decimal = implied prob. Professional bettors worldwide prefer decimals for their simplicity and lack of ambiguity.

Fractional Odds (3/2, 2/3)

Fractional odds are the traditional format in the United Kingdom and Ireland, deeply rooted in horse racing culture. They express the ratio of net profit to stake. At 3/2 ("three to two"), a $2 bet profits $3 (returning $5 total). At 2/5 ("two to five"), a $5 bet profits $2 (returning $7 total). Evens (1/1) is the equivalent of +100 American or 2.00 Decimal. While fractionals feel intuitive for simple ratios, they become awkward at unusual prices. Try comparing 11/8 vs 6/4 quickly. This is why even UK bookmakers increasingly display decimal odds alongside fractional.

A Brief History and Geography of Odds Formats

American odds evolved from the US pari-mutuel racing system and became standard as Las Vegas sportsbooks grew in the mid-20th century. Decimal odds originated in continental Europe and spread to Australasia through the totalizator (tote) betting system. Fractional odds are the oldest format, dating back to 18th-century British horse racing bookmakers who quoted prices as ratios at the track. Today, most online sportsbooks let you toggle between all three, but knowing which format is native to which market helps you spot pricing anomalies when line-shopping across international books.

Implied Probability and Why It Matters

Every set of odds implies a probability that the outcome will occur. This is the single most important concept in sports betting. To find value, you compare the bookmaker's implied probability against your own estimated probability. The formulas are:

From American: Positive: 100 / (odds + 100). Negative: |odds| / (|odds| + 100).
From Decimal: 1 / decimal.
From Fractional (a/b): b / (a + b).

Overround and Vigorish Explained

In a fair market, the implied probabilities of all outcomes sum to exactly 100%. In reality, they sum to more, typically 103% to 108% at major sportsbooks. The excess is the overround (or vigorish/juice), and it represents the bookmaker's built-in margin. For example, a coin flip priced at -110 / -110 implies 52.38% + 52.38% = 104.76%. The 4.76% overround is the house edge. Understanding overround helps you identify which sportsbooks offer the sharpest lines: lower overround means less vig and better prices for you. Betting exchanges typically run 1-2% overround vs. 4-6% at traditional sportsbooks.

Quick Reference Table

American	Decimal	Fractional	Implied Prob
-500	1.200	1/5	83.33%
-300	1.333	1/3	75.00%
-200	1.500	1/2	66.67%
-110	1.909	10/11	52.38%
+100	2.000	1/1	50.00%
+150	2.500	3/2	40.00%
+200	3.000	2/1	33.33%
+300	4.000	3/1	25.00%
+500	6.000	5/1	16.67%

Step-by-Step Conversion Formulas

Knowing the conversion formulas lets you sanity-check any calculator and work the math in your head during live betting when speed matters. The backbone is the decimal format. It is the easiest to convert to and from.

American → Decimal:

Positive (+odds): Decimal = (odds / 100) + 1
Negative (-odds): Decimal = (100 / |odds|) + 1

Examples: +150 → (150/100) + 1 = 2.50. -200 → (100/200) + 1 = 1.50.

Decimal → American:

If decimal ≥ 2.00: American = (decimal - 1) × 100 (positive, +)
If decimal < 2.00: American = -100 / (decimal - 1) (negative, -)

Examples: 2.50 → (2.50-1) × 100 = +150. 1.50 → -100/(1.50-1) = -200.

Fractional (a/b) → Decimal:

Decimal = (a / b) + 1

Example: 3/2 → (3/2) + 1 = 2.50. 2/5 → (2/5) + 1 = 1.40.

Decimal → Fractional: Subtract 1, express as a simplified ratio.

Fractional = (decimal - 1) expressed as a/b

Example: 2.50 → 1.50 → 3/2. 1.333 → 0.333 → 1/3.

Odds → Implied Probability:

From decimal: IP = 1 / decimal
From American (positive): IP = 100 / (odds + 100)
From American (negative): IP = |odds| / (|odds| + 100)
From fractional (a/b): IP = b / (a + b)

Value Betting: Why Odds Conversion Matters

Converting odds to implied probability is the fundamental step in identifying value bets. A value bet exists when your estimated probability of an outcome is higher than the bookmaker's implied probability. The formula for expected value on a $1 stake is:

EV = (decimal_odds × your_prob) - 1

If you assess an outcome at 45% probability but the line is +150 (decimal 2.50, implied 40%), the EV per dollar is (2.50 × 0.45) - 1 = +0.125. That is a 12.5% edge, exceptional by any standard. Most winning bettors operate on edges of 2 to 5%. The key is building an accurate probability model and comparing it against the de-vigged line, not the raw implied probability which contains the bookmaker's margin.

Line shopping magnifies this edge. The same game at -110 at one book vs. -105 at another is the difference between a 4.55% vig and a 2.44% vig, more than two percentage points of pure value, compounded over every bet you place.

Frequently Asked Questions

Q: What is the difference between +100 American odds and 2.00 decimal odds?

A: They are identical. +100 means you profit $100 on a $100 bet and collect $200 total. Decimal 2.00 means your $100 bet returns $200 total (stake included). Both imply exactly 50% probability before vig. The +100 / -100 level is called "even money."

Q: Why do different sportsbooks show different odds for the same game?

A: Each book sets its own lines based on its own risk exposure, sharp action received, and market positioning strategy. Books shade lines to balance their liability, not to reflect true probability. This creates line-shopping opportunities. Always compare at least 3-4 books before placing. A half-point or a few cents in decimal can mean significant EV difference at scale.

Q: How do I convert -110 / -110 (standard spread) into an overround?

A: Each side at -110 implies 110/(110+100) = 52.38% probability. Two sides × 52.38% = 104.76% total. The overround is 4.76%, meaning the book holds roughly 4.76 cents per dollar bet in the long run. The equivalent decimal odds are 1.909 per side.

Q: What are "Pinnacle-style" odds and why do pros prefer them?

A: Sharp-friendly books like Pinnacle run very low overrounds, typically 1.5-2.5% on major markets, compared to 4-6% at recreational books. They accept large bets and rarely limit winners. The tradeoff is a smaller bonus/promotion structure. Professionals treat sharp books' closing lines as benchmarks: if your bet closes at a better number than you got, you had positive line value (PLV).

Q: Why can't I just use the raw implied probability to find value?

A: The raw implied probability includes the bookmaker's margin. If a book runs 5% overround and you compare your model's 52% estimate to their implied 53%, you might think you lack value, but after removing the 5% vig, their true probability is closer to 50.5%, and your 52% is well above it. Always strip the vig first using a no-vig calculator before comparing to your probability estimates.

Related Tools

Strip the vig from any line with the No-Vig Calculator, convert odds directly to win probability with the Implied Probability Calculator, or check whether a bet is +EV using the EV Calculator.

Take Your Edge Further

GAMB·8 gives you automated bot strategies, real-time analytics, poker HUD, and sports intelligence: all the tools to find and exploit +EV opportunities.