Are +100 and −100 the same price?

Yes. Both are even money — a winning $100 bet returns $100 profit either way, or 2.00 in decimal. American odds have no values between −100 and +100, which is why converting through decimal avoids a special case.

Why do the two sides of a market add up to more than 100%?

The excess is the bookmaker’s margin, usually called the vig or overround. A market priced −110 / −110 implies 104.76% in total, so 4.76% of the implied probability is margin rather than likelihood. Use the no-vig calculator to strip it out.

Is implied probability the real chance of the outcome?

No. It is the probability the price implies, margin included, so it is always higher than the bookmaker’s own estimate of the true chance. Treat it as the number you have to beat, not as a forecast.

Why is my fractional result not exact?

Fractional odds are conventionally printed as simple fractions. −110 is 10/11 in a betting shop, not 909/1000, so this tool finds the closest fraction with a denominator up to 100 rather than an arithmetically exact one.

Odds Converter

Convert a price between American, decimal and fractional odds, and see the probability it implies.

Enter a price

Change the format at any time — the price is kept, not reinterpreted.

Common prices

Implied probability

52.38%

What the price implies before the bookmaker’s margin is removed. Both sides of a market add up to more than 100% — that excess is the vig.

American: -110
Decimal: 1.9091
Fractional: 10/11
Break-even win rate: 52.38%

Runs entirely in your browser · nothing is sent or saved

What are American, decimal and fractional odds?

Three notations for the same thing: how much a bet pays, and what chance the price implies.

American odds are quoted against $100 — +150 wins $150 on a $100 stake, −150 risks $150 to win $100. Decimal odds give the total return per unit staked, so 2.50 returns $2.50 for every $1 including the stake. Fractional odds show profit against stake: 3/2 pays three units for every two risked.

+150, 2.50 and 3/2 are the same price. American is standard in the US, decimal across Europe and Australia, fractional in UK racing.

How it works

The three formats are the same information written three ways. American odds describe money: +150 means a $100 stake wins $150, and −150 means you must risk $150 to win $100. Decimal odds describe the total return per unit staked, stake included, so 2.50 returns $2.50 for every $1. Fractional odds describe profit against stake, so 3/2 wins three for every two risked.

Every conversion here routes through decimal. That is not an implementation detail you can ignore: American odds have a hole in them. Nothing exists between −100 and +100, and both ends of that gap describe the same price — even money. Decimal is continuous, so it can carry any price without a special case, which is why it is the format the maths is done in even when it is not the format shown.

The implied probability is the most useful number on this page and the most misread. It is what the price says the chance is, and it is deliberately overstated: add up both sides of a two-way market and you get more than 100%. A pair of −110s implies 52.38% each, or 104.76% together. That extra 4.76% is the bookmaker’s margin, and it is why beating the closing price matters more than winning any single bet.

The formula

American → decimal
  positive:  decimal = 1 + american / 100
  negative:  decimal = 1 + 100 / |american|

Decimal → American
  decimal ≥ 2:  american = (decimal − 1) × 100
  decimal < 2:  american = −100 / (decimal − 1)

Implied probability
  probability = 1 / decimal

  positive american:  100 / (american + 100)
  negative american:  |american| / (|american| + 100)

Decimal is the pivot; every other format converts through it.

A worked example

Take +150. In decimal that is 1 + 150/100 = 2.50, and as a fraction, 3/2. The implied probability is 1 / 2.50 = 40%, which you can also read straight off the American form: 100 / (150 + 100) = 40%.

Now −150. Decimal is 1 + 100/150 = 1.667, fractional 2/3, and the implied probability is 150 / (150 + 100) = 60%.

Those two add to exactly 100%, because +150 and −150 are a fair market with no margin in it — which is not a market any bookmaker offers. The real version is closer to −110 / −110: 52.38% and 52.38%, adding to 104.76%. You are being asked to win 52.38% of coin flips.

Common questions

Are +100 and −100 the same price?: Yes. Both are even money — a winning $100 bet returns $100 profit either way, or 2.00 in decimal. American odds have no values between −100 and +100, which is why converting through decimal avoids a special case.
Why do the two sides of a market add up to more than 100%?: The excess is the bookmaker’s margin, usually called the vig or overround. A market priced −110 / −110 implies 104.76% in total, so 4.76% of the implied probability is margin rather than likelihood. Use the no-vig calculator to strip it out.
Is implied probability the real chance of the outcome?: No. It is the probability the price implies, margin included, so it is always higher than the bookmaker’s own estimate of the true chance. Treat it as the number you have to beat, not as a forecast.
Why is my fractional result not exact?: Fractional odds are conventionally printed as simple fractions. −110 is 10/11 in a betting shop, not 909/1000, so this tool finds the closest fraction with a denominator up to 100 rather than an arithmetically exact one.

The guide behind this calculator

Related calculators

For informational and analytical purposes only. These tools do not predict outcomes and do not recommend wagers.