Bookmaker’s Overround
Bookmakers are profit making businesses. To keep them profitable they need to write in a certain amount of margin into each market they offer prices on. An overround of 110% means that the customer must stake a total of €110 spread out over all the selections to guarantee himself a return of €100 regardless of the result. In this way the bookmaker expects to make a profit of €10 for every €110 turnover.
We will first look at how margin is calculated:
For odds displaying in the fractional form X/Y the margin on this is calculated using the formula Y/(X+Y). e.g. the margin on 6/4 = 4/(6+4) = 4/10 = 40%.
For odds displaying in the decimal format this calculation is even easier as you just divide 1 by the decimal and display as a percentage. e.g. the margin on 2.5 (this is the decimal form of 6/4) is 1/(2.5) = 40%.
So if a bookmaker offers odds on a 3-way market with odds on the 3 selections of 1/1 (=50%), 2/1 (=33.33%) and 3/1 (=25%). This results in an overround of 108.33%.
The size of the overround depends on the number of selections and how high profile the event is. These can range from approximately 104% for the Superbowl match betting, 106% for Premier League Soccer match betting, 111% on lower profile soccer leagues, 125% on greyhound races with 6 selections, 130% on soccer correct score market to in the region of 160% on a golf tournament with over 100 golfers. The higher the overround the more margin the bookmakers expect to make from a market, making it increasingly difficult for the bettor to have a profitable bet.
Please see Genie’s chart that converts prices from fractional to decimal odds and displaying the margins on these odds.
| FRACTIONAL ODDS | DECIMAL ODDS | MARGIN |
| 1/100 | 1.01 | 99.01% |
| 1/66 | 1.02 | 98.51% |
| 1/50 | 1.02 | 98.04% |
| 1/33 | 1.03 | 97.06% |
| 1/25 | 1.04 | 96.15% |
| 1/20 | 1.05 | 95.24% |
| 1/16 | 1.06 | 94.12% |
| 1/12 | 1.08 | 92.31% |
| 1/10 | 1.10 | 90.91% |
| 1/9 | 1.11 | 90.00% |
| 1/8 | 1.13 | 88.89% |
| 1/7 | 1.14 | 87.50% |
| 1/6 | 1.17 | 85.71% |
| 1/5 | 1.20 | 83.33% |
| 2/9 | 1.22 | 81.82% |
| 1/4 | 1.25 | 80.00% |
| 2/7 | 1.29 | 77.78% |
| 3/10 | 1.30 | 76.92% |
| 1/3 | 1.33 | 75.00% |
| 4/11 | 1.36 | 73.33% |
| 2/5 | 1.40 | 71.43% |
| 4/9 | 1.44 | 69.23% |
| 1/2 | 1.50 | 66.67% |
| 8/15 | 1.53 | 65.22% |
| 4/7 | 1.57 | 63.64% |
| 8/13 | 1.62 | 61.90% |
| 2/3 | 1.67 | 60.00% |
| 8/11 | 1.73 | 57.89% |
| 4/5 | 1.80 | 55.56% |
| 5/6 | 1.83 | 54.55% |
| 10/11 | 1.91 | 52.38% |
| 1/1 | 2.00 | 50.00% |
| 11/10 | 2.10 | 47.62% |
| 6/5 | 2.20 | 45.45% |
| 5/4 | 2.25 | 44.44% |
| 13/10 | 2.30 | 43.48% |
| 11/8 | 2.38 | 42.11% |
| 7/5 | 2.40 | 41.67% |
| 3/2 | 2.50 | 40.00% |
| 8/5 | 2.60 | 38.46% |
| 13/8 | 2.63 | 38.10% |
| 17/10 | 2.70 | 37.04% |
| 7/4 | 2.75 | 36.36% |
| 9/5 | 2.80 | 35.71% |
| 15/8 | 2.88 | 34.78% |
| 2/1 | 3.00 | 33.33% |
| 21/10 | 3.10 | 32.26% |
| 11/5 | 3.20 | 31.25% |
| 9/4 | 3.25 | 30.77% |
| 23/10 | 3.30 | 30.30% |
| 12/5 | 3.40 | 29.41% |
| 5/2 | 3.50 | 28.57% |
| 13/5 | 3.60 | 27.78% |
| 11/4 | 3.75 | 26.67% |
| 14/5 | 3.80 | 26.32% |
| 3/1 | 4.00 | 25.00% |
| 16/5 | 4.20 | 23.81% |
| 10/3 | 4.33 | 23.08% |
| 7/2 | 4.50 | 22.22% |
| 15/4 | 4.75 | 21.05% |
| 4/1 | 5.00 | 20.00% |
| 9/2 | 5.50 | 18.18% |
| 5/1 | 6.00 | 16.67% |
| 11/2 | 6.50 | 15.38% |
| 6/1 | 7.00 | 14.29% |
| 13/2 | 7.50 | 13.33% |
| 7/1 | 8.00 | 12.50% |
| 15/2 | 8.50 | 11.76% |
| 8/1 | 9.00 | 11.11% |
| 9/1 | 10.00 | 10.00% |
| 10/1 | 11.00 | 9.09% |
| 11/1 | 12.00 | 8.33% |
| 12/1 | 13.00 | 7.69% |
| 14/1 | 15.00 | 6.67% |
| 16/1 | 17.00 | 5.88% |
| 18/1 | 19.00 | 5.26% |
| 20/1 | 21.00 | 4.76% |
| 22/1 | 23.00 | 4.35% |
| 25/1 | 26.00 | 3.85% |
| 28/1 | 29.00 | 3.45% |
| 33/1 | 34.00 | 2.94% |
| 40/1 | 41.00 | 2.44% |
| 50/1 | 51.00 | 1.96% |
| 66/1 | 67.00 | 1.49% |
| 80/1 | 81.00 | 1.23% |
| 100/1 | 101.00 | 0.99% |
| 125/1 | 126.00 | 0.79% |
| 150/1 | 151.00 | 0.66% |
| 200/1 | 201.00 | 0.50% |
| 250/1 | 251.00 | 0.40% |
| 300/1 | 301.00 | 0.33% |
| 400/1 | 401.00 | 0.25% |
| 500/1 | 501.00 | 0.20% |
| 750/1 | 751.00 | 0.13% |
| 1000/1 | 1001.00 | 0.10% |