The bookmaker’s margin (overround or vigorish) is the percentage built into every market that ensures a long-term profit for the house. Understanding and minimising the margin you pay is the single most impactful change a regular punter can make. This guide compares typical overrounds across GRAI-licensed operators by sport and market type.
What Is Overround and Why Does It Matter?
If you add up the implied probabilities of all outcomes in a market (by converting odds to percentages), they should total 100% at fair value. They never do — they typically total 103–108%. That excess is the overround: the bookmaker’s built-in profit. On a coin-flip market priced at 10/11 each side (implied probability 52.4% each = 104.8% total), the overround is 4.8%.
| Sport / Market | Tight-Margin Operator | Standard Irish Bookmaker |
|---|---|---|
| PL 1X2 (average) | 4–5% | 5.5–6.5% |
| Champions League 1X2 | 4–5% | 5–6% |
| Horse racing (8-runner) | 6–7% | 7–9% |
| GAA football (3-way) | 7–9% | 8–10% |
| Tennis (2-way) | 3–4% | 4–6% |
| Golf outright (20 runners) | 25–35% | 30–40% |
| Correct score | 15–20% | 18–22% |
How to Calculate Overround Yourself
For a 1X2 football market: convert each price to implied probability (100 ÷ (decimal odds × 100)). For example, 2.10 home win = 47.6%, 3.40 draw = 29.4%, 3.60 away win = 27.8%. Total = 104.8%. Overround = 4.8%. Our margin calculator automates this — paste in any three prices and it returns the overround instantly.
Sports Where the Gap Is Largest
Outright and specials markets (correct score, first goalscorer, golf outright) carry the highest margins — often 20–40%. These markets exist primarily for entertainment; the expected value is poor across all operators. The tightest margins are on major 1X2 football and head-to-head tennis, where competition between operators is fiercest and sharp bettor activity keeps prices honest.
Accumulator Margins: Why They Compound
On an accumulator, overrounds multiply. A 5-team acca where each leg has a 5% margin produces a combined overround of approximately 27.6% (1.05^5). Every additional leg increases the mathematical edge against you exponentially. This is why acca boosts offer genuine value: they are partially refunding the compounded margin. Even so, accumulators carry negative expected value across all operators.
Frequently Asked Questions
The margin (overround or vigorish) is the percentage added to a market that guarantees the bookmaker a profit long-term. On a 1X2 football market, overrounds of 4–6% are typical at GRAI-licensed operators.
Tennis head-to-head markets typically have the lowest margins (3–5%) because they are simple two-outcome markets. Football 1X2 is 4–6%. Outright markets (golf, horse racing with many runners) carry the highest margins.
Convert each outcome’s decimal odds to implied probability (1 ÷ decimal odds), sum all probabilities, subtract 100% — the remainder is the overround. Our margin calculator does this automatically.
No. Margins vary significantly between operators, especially on football. Tight-margin operators run 4–5% on Premier League 1X2; others run 5.5–6.5% on the same market. Over hundreds of bets, this difference is substantial.
Yes. Each additional leg in an accumulator multiplies the overround. A 5-leg acca with 5% margin per leg results in a combined overround of approximately 27.6%. Acca boosts partially offset this.