Odds Calculator & Converter for Ireland: Decimal, Fractional, American + Margin

Updated 15 Oct 2026 · By the IrishBetGuide team

Before you back anything, know what the price is actually saying. Pop the odds in below in any format and you'll get the conversions, the implied chance, and what your stake returns in €. Scroll down and you can check how much margin the bookie has baked into a whole market.

Bookmaker margin checker

Type the odds for every outcome of one market (2 or 3 outcomes, e.g. home / draw / away). Leave the third box empty for 2-way markets.

The three odds formats, quickly

Decimal (2.50) is your total return per 1 staked, stake included. Fractional (6/4) is profit over stake, so 6/4 means 6 profit for every 4 staked, which is 2.50 in decimal. American uses 100 as the anchor: +150 means 150 profit on a 100 stake, and -200 means you stake 200 to win 100. Irish bookies and the racing papers still quote fractions (5/2, 11/8, evens), so the calculator takes those directly.

Implied probability: the number that matters

Implied probability is just 1 divided by the decimal odds. A price of 2.50 implies 40%. If you honestly think the outcome happens more often than the price implies, that's value; if not, the price is against you, however exciting the team news looks.

How much is the bookie taking? (worked example)

Say a Munster v Leinster URC game is priced 2.10 / 3.30 / 3.60. Add up the implied chances: they come to 105.7%, not 100%. That extra 5.7 points is the overround, and it works out to a margin of about 5.4% built into the prices. Strip it out and the "fair" odds would be roughly 2.22 / 3.49 / 3.81. These are example prices, not live odds; paste real prices into the margin checker above to test any market you're looking at.

Rule of thumb: main markets on big matches usually carry the thinnest margins; props, correct scores and long-range outrights usually carry fat ones. Lower margin means more of your money is going to the outcome and less to the house.

Using it with accumulators

Each leg of an acca carries its own margin, and they multiply. Our accumulator calculator shows the combined odds and the real chance of every leg landing.

Where the numbers come from

The calculator runs in your browser and uses standard formulas: decimal = 1 + fractional; American positive = (decimal − 1) × 100; American negative = −100 ÷ (decimal − 1); implied probability = 1 ÷ decimal; margin = 1 − 1 ÷ (sum of implied probabilities). Fractions are rounded to the nearest simple fraction. See how we work for our methodology.

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