How Bookmaker Margins Work
A bookmaker margin (also called the overround, vig or juice) is the built-in edge a bookie adds to a market so the prices add up to more than 100%. It is the difference between the true probability of an outcome and the price you actually get. The lower the margin, the more of your stake stays with you over time. Across the Irish-facing operators we track, sampled margins range from about 4.3% at Betfair to roughly 8.4% at LiveScore Bet — and on a €100 stake, that gap is real money. This guide shows you how to read a margin, how to calculate it yourself, and which bookmakers price sharper on the sampled markets.
What the overround actually is
Every set of odds implies a probability. Decimal odds of 2.00 imply a 50% chance (1 ÷ 2.00 = 0.50). If a coin toss were priced fairly, both sides would be 2.00 and the two implied probabilities would sum to exactly 100%.
Bookmakers do not price fairly. They shave the odds so the implied probabilities add up to more than 100%. That surplus is the margin. On a two-way market you might see both sides at 1.91 instead of 2.00 — each implies 52.4%, and together they sum to 104.8%. That extra 4.8% is the overround: the theoretical cut the bookie keeps regardless of who wins.
The margin is not a fee you see deducted. It is baked into the price before you ever place a bet. That is why comparing odds across bookmakers matters more than chasing a sign-up offer once.
How to calculate a margin yourself
The method is the same for any market. Convert each price to its implied probability (1 ÷ decimal odds), add them up, then subtract 100%.
Worked example — a Premier League match priced by a bookmaker: - Home win 2.10 → 1 ÷ 2.10 = 47.62% - Draw 3.40 → 1 ÷ 3.40 = 29.41% - Away win 3.75 → 1 ÷ 3.75 = 26.67%
Add them: 47.62 + 29.41 + 26.67 = 103.70%. The margin here is 3.70% over the fair 100%.
For a market with more outcomes — say 20 runners in a handicap at the Galway Races — the same maths applies, but the sum of implied probabilities is usually much higher, because horse racing and other multi-runner markets carry heavier margins than a three-way football result.
A quick rule of thumb: the more selections in a market, the more room a bookmaker has to load margin into each price. Match result markets are typically tighter than first goalscorer, correct score or outright winner markets.
Implied Probability Calculator
What a margin costs you on a €100 stake
Margin compounds over many bets, so the cleanest way to feel it is to compare two prices for the same outcome.
Suppose the fair price for a selection is 2.00 (a true 50% chance). - At a bookmaker offering 1.95, a winning €100 bet returns €195, so €95 profit. - At a sharper price of 1.98, the same €100 winner returns €198, so €98 profit.
That is €3 more profit on a single winning bet, purely from a better price. Now scale it: place 200 bets of €100 across a season and a 3% pricing difference is €600 of expected value you either keep or hand over. This is why the margin figure matters far more than a one-off free bet.
The averaged sampled margins we track make the point concretely: - Betfair — 4.29% average margin (213 markets sampled) - Unibet — 5.73% (191 sampled) - Ladbrokes — 5.83% (193 sampled) - Betway — 6.32% (195 sampled) - Paddy Power — 6.93% (195 sampled) - William Hill — 6.96% (219 sampled) - 888sport — 7.13% (219 sampled) - bet365 — 7.44% (30 sampled) - BoyleSports — 7.51% (195 sampled) - BetVictor — 7.51% (188 sampled) - LiveScore Bet — 8.37% (193 sampled)
Treat these as a guide, not a guarantee. Margins move by sport, by market and by how close it is to kick-off. bet365's figure in particular comes from a small sample of 30 markets, so it carries less weight than operators sampled across 190+ markets.
Why margins differ between bookmakers
Two factors drive most of the variation. First, business model. Betfair operates an exchange as well as a sportsbook, and its 4.29% sampled margin and 53% best-price share reflect that exchange-style pricing tends to run tighter than a traditional sportsbook. Second, market priority. A bookmaker can price the Premier League or Champions League sharply to attract turnover, then run fatter margins on niche markets where fewer bettors compare prices.
Best-price share tells a related story: it is how often an operator posts the top price in the sampled markets. Betfair leads at 53%, followed by Ladbrokes at 22%, Unibet and William Hill both around 17%. BetVictor (6%) and LiveScore Bet (10%) top-price far less often, which lines up with their heavier average margins.
One caveat on interpretation: a low average margin does not automatically mean every price is best. Check the specific market and selection you want, not just the headline figure.
Where to look for tighter margins
If you value price above everything, the sampled data points to Betfair, Unibet and Ladbrokes for the lowest average margins on the markets we track. Betfair also posts the top price most often, which is what you want if you shop around per bet.
If you prioritise depth, live capability or the app experience, you may accept a slightly higher margin. bet365 rates highest in our data for market coverage (9.6) and sports depth (9.5), and Paddy Power (regulated by the GRAI) scores 8.8 for its app — but both carry higher sampled margins than Betfair. That is the trade-off spelled out plainly: choose the tight-margin operator if you bet high volume and compare prices; choose the deep-coverage operator if you want more markets, live streaming or Bet Builder on the same slip.
The practical takeaway for Irish bettors: hold accounts at two or three bookmakers, compare the price for your exact selection, and take the best one. That habit beats any single loyalty. See our odds and comparison pages to line up prices side by side.
Margins on football, horse racing and other sports
Margins are not uniform across sports. Match result markets on major football leagues — Premier League, Serie A, Ligue 1, Champions League — are usually the tightest, because they attract the most turnover and the most price comparison.
Horse racing carries higher margins on average, especially in big-field handicaps where 15–20 runners give the bookmaker more selections to load. GAA, rugby, tennis and golf outright markets also tend to run heavier margins than a simple two-way or three-way football result. When you calculate a margin, always compare like markets: a golf outright with 100+ names in the field is not comparable to a tennis match with two players.
If you mainly bet a specific sport, it is worth sampling a handful of that sport's markets across your shortlisted bookmakers rather than relying on an overall average.
FAQ
What is a bookmaker margin?
It is the amount by which a bookmaker's odds imply more than 100% probability across a market. Also called the overround, vig or juice, it is the built-in edge the bookie keeps regardless of the result. On the operators we track, sampled averages run from about 4.3% up to 8.4%.
How do I calculate the overround?
Convert each price to its implied probability with 1 ÷ decimal odds, add them all up, then subtract 100%. For example, a football match at 2.10 / 3.40 / 3.75 gives 47.62% + 29.41% + 26.67% = 103.70%, so the margin is 3.70%.
Which bookmaker has the lowest margins in Ireland?
On our sampled markets, Betfair has the lowest average margin at 4.29%, followed by Unibet at 5.73% and Ladbrokes at 5.83%. Betfair also posts the top price most often (about 53% of sampled markets). Margins vary by sport and market, so always check your specific selection.
Does a lower margin mean I win more?
Not directly — the outcome still decides whether you win a single bet. But a lower margin means better prices, so over many bets you keep more of your expected value. A 3% pricing difference on 200 bets of €100 is around €600 of expected value.
Why do horse racing margins look higher than football?
Multi-runner markets give bookmakers more selections to spread margin across. A big-field handicap can carry a much higher overround than a three-way football result. Compare like markets when judging value.
Are all these bookmakers legal in Ireland?
The operators listed here are licensed to serve Irish bettors, and several — including Paddy Power, BoyleSports and Novibet — are noted as regulated by the Gambling Regulatory Authority of Ireland (GRAI). The minimum betting age in Ireland is 18. See our legal betting sites page for more.