Odds Converter: American, Decimal, Fractional & Implied Probability Calculator

Different sportsbooks display the same wager in different formats. American books default to American odds (-110, +150). European exchanges show decimal odds (1.91, 2.50). UK bookmakers prefer fractional odds (10/11, 6/4). And every odds line implies a probability that lets you compare across formats and against your own true-probability estimates.

This odds converter handles all four. Type in any one, see the others. Below the tool, you’ll find the math behind each conversion — useful when you want to verify a calculation by hand or build it into your own model.

How to Convert Between Odds Formats

The four formats display the same information differently. Once you understand decimal odds as the underlying form, every conversion is a single arithmetic step.

American to Decimal

For negative American odds: decimal = 1 + 100 / |american|

For positive American odds: decimal = 1 + american / 100

Examples: -110 → 1 + 100/110 = 1.909. +150 → 1 + 150/100 = 2.50.

Decimal to American

If decimal ≥ 2: american = (decimal − 1) × 100 (positive)

If decimal < 2: american = −100 / (decimal − 1) (negative)

Examples: 2.50 → +150. 1.909 → −110.

Decimal to Implied Probability

The simplest conversion in sports betting:

implied probability % = 100 / decimal

Example: 1.909 → 100/1.909 = 52.38%.

Fractional Odds

Fractional odds (e.g., 10/11, 6/4) show profit-to-stake ratio. To convert:

decimal = 1 + (numerator / denominator)

Examples: 10/11 → 1 + 10/11 = 1.909. 6/4 → 1 + 6/4 = 2.50.

Implied Probability Calculator: Why It Matters Most

Of the four formats, implied probability is the only one that lets you compare a wager against your own true-probability estimate. That’s the foundation of +EV betting: identify spots where the sportsbook’s implied probability is lower than what you believe the true probability of an outcome is.

If a sportsbook prices a team at -110 (52.38% implied), and your model says the team should win 55% of the time, you have a 2.62% positive expected value on that wager. Convert prices to implied probability across multiple sportsbooks, find the most favorable, and your closing line value improves over time.

Reduced Juice -105 vs Standard -110: A Real Comparison

Why bet105 prices core markets at -105 instead of the industry-standard -110: the implied-probability difference is small per bet but compounds across volume. The table below makes the price gap concrete.

Metric	Standard (-110)	Reduced Juice (-105)
Decimal odds	1.909	1.952
Implied probability	52.38%	51.22%
Break-even win rate required	52.38%	51.22%
Total payout on $100 stake	$190.91	$195.24
Edge surrendered to bettor per wager	—	~1.16%

For deep coverage of the pricing model, see the Low Vig / Reduced Juice hub.

The Sportsbook’s Margin in Implied Probability

Both sides of a two-way market always sum to more than 100% implied probability. That excess is the overround — the structural pricing buffer that lets the sportsbook profit on balanced action.

Standard -110/-110 odds: 52.38% + 52.38% = 104.76% overround. The 4.76% above 100% reflects the sportsbook’s pricing edge. The actual realized margin (or “hold”) on any individual market depends on how balanced the action is, but at a balanced book, the long-run margin trends toward the implied edge.

Reduced-juice -105/-105 odds: 51.22% + 51.22% = 102.44% overround. Roughly half the overround of the standard market.

This is why sharp bettors track implied probability across books and target the lowest-vig pricing. For arbitrage opportunities specifically — where two sides at different books sum to less than 100% — see the arbitrage betting hub.

Frequently Asked Questions

What’s the easiest format to use as a beginner?

Decimal odds. They show the total return per $1 wagered (including your stake), so a $100 bet at 1.91 returns $191. No mental math required — multiply your stake by the decimal odds and that’s your full payout.

Why do American sportsbooks use American odds instead of decimal?

Convention. American odds clearly express the asymmetry between favorites and underdogs in two-way markets — negative odds show how much you risk to win $100, positive odds show how much you’d win on a $100 bet. Decimal odds are more common in Europe because European markets feature more moneyline-style bets at varied prices, where decimal scales cleanly.

How do I convert -110 to implied probability?

Use the formula: implied probability = bet amount ÷ (bet amount + win amount). At -110: $110 / ($110 + $100) = 52.38%. Or use the calculator above and enter -110 in the American Odds field.

What’s a “no-vig” or “fair” implied probability?

The no-vig probability strips the sportsbook’s overround out of both sides of a market, leaving the implied probability the book itself estimates for the outcome. To calculate: take the implied probability of one side and divide by the sum of both sides’ implied probabilities.

For example, if a market shows -110/-110 (both sides at 52.38%): no-vig = 52.38 / (52.38 + 52.38) = exactly 50%. That’s the fair price stripped of vig.

Are fractional odds still used?

Yes, primarily in UK and Irish horse racing markets. Most modern sportsbooks let you toggle the display format. Fractional odds were the original format historically — a 6/4 horse pays $6 profit for every $4 wagered, plus your $4 stake back.

Related Tools

Pair this odds converter with the rest of the bet105 tool kit (calculators rolling out over the coming weeks):

• EV calculator (coming soon) — turn implied probability + your true-probability estimate into a per-bet expected-value figure
• Arbitrage calculator (coming soon) — when two-sided implied probability sums to less than 100%, get the optimal stake split for a guaranteed return
• Parlay calculator (coming soon) — combined odds and implied probability across multiple legs
• Kelly Criterion calculator (coming soon) — convert your edge into the mathematically optimal stake size

For the strategy framework that ties these together, see the expected value betting hub.