Betting odds tell you how much you will win relative to your stake. In Ireland you will encounter three formats: fractional (traditional), decimal (now most common online), and American moneyline (less common, used by US sports sites). All three describe the same probability — they are just presented differently.
Fractional Odds (Traditional Irish Format)
Written as X/Y (e.g. 5/1, 7/2, 11/4). The left number is profit; the right is stake. At 5/1: stake €10, win €50 profit + €10 stake back = €60 total return. At 7/2: stake €10, win €35 profit + €10 back = €45 total return. If the right number is bigger than the left (e.g. 1/2), the selection is odds-on — you risk more than you win.
Decimal Odds (Standard Online Format)
Written as a single number (e.g. 6.00, 4.50, 1.50). Multiply your stake by the decimal to get total return including stake. At 6.00: €10 × 6.00 = €60 total (€50 profit). To convert from fractional: (5/1) = 5 ÷ 1 + 1 = 6.00. Decimal odds include your stake in the figure; fractional odds do not.
Odds Conversion Table
| Fractional | Decimal | American | Implied Probability | €10 Return |
|---|---|---|---|---|
| 1/4 | 1.25 | -400 | 80% | €12.50 |
| 1/2 | 1.50 | -200 | 67% | €15.00 |
| Evens (1/1) | 2.00 | +100 | 50% | €20.00 |
| 2/1 | 3.00 | +200 | 33% | €30.00 |
| 5/1 | 6.00 | +500 | 17% | €60.00 |
| 10/1 | 11.00 | +1000 | 9% | €110.00 |
| 33/1 | 34.00 | +3300 | 3% | €340.00 |
Implied Probability and Value
Implied probability = 1 ÷ decimal odds × 100. At 6.00 decimal, implied probability = 1/6 = 16.7%. If you believe the true probability is higher than 16.7%, you have a value bet. If you think the true probability is lower, the bet has negative value. The bookmaker builds in a margin (usually 4–8% on main markets), so implied probabilities across a market add up to more than 100%.
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Decimal odds are now standard across most online bookmakers. Fractional odds remain common in Irish and UK horse racing tradition. Most apps let you switch between formats in settings.