Odds Converter

Frequently Asked Questions

How do I convert American odds to decimal?

Positive: decimal = (American ÷ 100) + 1, so +150 = 2.50. Negative: decimal = (100 ÷ |American|) + 1, so −200 = 1.50. This tool is for educational understanding, not betting advice.

What is implied probability?

Implied probability = 1 ÷ decimal odds (×100%). Decimal 2.50 implies 40%. It reflects the bookmaker's price including margin, not a true objective probability of the outcome.

What are no-vig (fair) odds?

Removing the bookmaker margin normalizes the implied probabilities of all outcomes to sum to 100%, giving a "fair" price for comparison. It is an analytical tool, not a guarantee of winning.

How do fractional odds relate to the others?

Fractional 5/2 means profit of 5 for every 2 staked, equal to decimal 3.50 and American +250. Understanding formats helps you read prices; please gamble responsibly and within limits.

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Sports & Betting Disclaimer: Informational only. Not betting advice.

This calculator is for informational and educational purposes only and is not betting, gambling, or financial advice. It does not predict outcomes or guarantee returns. Gambling involves risk and can be addictive, so never wager more than you can afford to lose. You are responsible for complying with the gambling laws in your jurisdiction and must be of legal age. If gambling is a problem for you, contact a support service such as 1-800-GAMBLER.

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How This Calculator Works

This converter is for informational and educational purposes only and is not betting advice - please gamble responsibly. Sportsbooks quote the same price in three notations. Decimal odds state the total return per 1 unit staked, so a 2.50 price returns 2.50 (1.50 profit + 1.00 stake). American odds use a +/− convention: a positive number is the profit on a 100 stake, and a negative number is the stake needed to profit 100. Fractional odds (UK style) state profit÷stake, so 5÷2 means 5 profit for every 2 risked. The common pivot is decimal odds: from decimal D the implied probability is simply 1 ÷ D, expressed here as a percentage. That implied figure is the book's break-even rate - the price already bakes in the bookmaker margin, so it is always slightly higher than a truly fair probability.

Formula / Method

From American odds A: if A > 0, D = 1 + A ÷ 100; if A < 0, D = 1 + 100 ÷ |A|. From fractional N÷Den: D = 1 + N ÷ Den. Implied probability % = 100 ÷ D. To go back to American: if D ≥ 2.00, A = +(D − 1) × 100; if D < 2.00, A = −100 ÷ (D − 1). For a two−way market the raw implied probabilities of both sides sum to more than 100% - that excess is the overround. Dividing each side's raw probability by the sum removes the margin and yields no−vig fair odds, the book's honest estimate of each outcome once its built−in edge is stripped out.

Worked Example

Take American −110. Since it is negative, D = 1 + 100 ÷ 110 = 1.909. Implied probability = 100 ÷ 1.909 ≈ 52.4%. As a fraction that is roughly 10÷11. Now suppose the other side is also −110 (D = 1.909, implied 52.4%). The two raw probabilities sum to 104.8%, an overround of 4.8%. Removing the vig: each fair probability = 52.4 ÷ 104.8 ≈ 50.0%, so the fair price on each side is decimal 2.00 (American +100). The 4.8% gap between 52.4% and 50.0% is the bookmaker's theoretical hold on a balanced book.

Common Mistakes

Treating implied probability as a true probability - it includes the vig and overstates each side.

Entering decimal odds below 1.00; decimal odds always exceed 1 because they include the returned stake.

Confusing fractional profit/stake with decimal total return: 1÷1 (evens) is decimal 2.00, not 1.00.

Forgetting the American sign - −150 and +150 are very different prices and probabilities.

Comparing prices across books without first removing the vig, which makes a fair line look like an edge.

Tips & FAQ

Which format is "best"? They are mathematically identical; decimal is easiest for computing payout and probability, which is why it is used as the pivot here, while American is the US convention and fractional the traditional UK one. Why does fractional look approximate? Many decimal prices have no exact small fraction, so the tool finds the closest tidy ratio - the decimal and implied figures are exact and should be treated as authoritative. Why show no−vig odds? Comparing the no−vig fair line to the price you can actually get is the foundation of value betting and line shopping; if a different book offers better than the fair price, that is where any theoretical edge lives. Does a low implied probability mean an underdog is "due"? No - that is the gambler's fallacy; each event is independent and the price already encodes the best available estimate. Remember that all of this is descriptive math: it does not predict outcomes, the house edge is real and persistent, and no conversion turns a negative−expectation wager into a winning long−run strategy. Treat betting as paid entertainment, set limits in advance, never chase losses, and seek help if it stops being fun.

Odds Converter

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