Overround (Betting Margin) Explained

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 ODDSDECIMAL ODDSMARGIN
1/1001.0199.01%
1/661.0298.51%
1/501.0298.04%
1/331.0397.06%
1/251.0496.15%
1/201.0595.24%
1/161.0694.12%
1/121.0892.31%
1/101.1090.91%
1/91.1190.00%
1/81.1388.89%
1/71.1487.50%
1/61.1785.71%
1/51.2083.33%
2/91.2281.82%
1/41.2580.00%
2/71.2977.78%
3/101.3076.92%
1/31.3375.00%
4/111.3673.33%
2/51.4071.43%
4/91.4469.23%
1/21.5066.67%
8/151.5365.22%
4/71.5763.64%
8/131.6261.90%
2/31.6760.00%
8/111.7357.89%
4/51.8055.56%
5/61.8354.55%
10/111.9152.38%
1/12.0050.00%
11/102.1047.62%
6/52.2045.45%
5/42.2544.44%
13/102.3043.48%
11/82.3842.11%
7/52.4041.67%
3/22.5040.00%
8/52.6038.46%
13/82.6338.10%
17/102.7037.04%
7/42.7536.36%
9/52.8035.71%
15/82.8834.78%
2/13.0033.33%
21/103.1032.26%
11/53.2031.25%
9/43.2530.77%
23/103.3030.30%
12/53.4029.41%
5/23.5028.57%
13/53.6027.78%
11/43.7526.67%
14/53.8026.32%
3/14.0025.00%
16/54.2023.81%
10/34.3323.08%
7/24.5022.22%
15/44.7521.05%
4/15.0020.00%
9/25.5018.18%
5/16.0016.67%
11/26.5015.38%
6/17.0014.29%
13/27.5013.33%
7/18.0012.50%
15/28.5011.76%
8/19.0011.11%
9/110.0010.00%
10/111.009.09%
11/112.008.33%
12/113.007.69%
14/115.006.67%
16/117.005.88%
18/119.005.26%
20/121.004.76%
22/123.004.35%
25/126.003.85%
28/129.003.45%
33/134.002.94%
40/141.002.44%
50/151.001.96%
66/167.001.49%
80/181.001.23%
100/1101.000.99%
125/1126.000.79%
150/1151.000.66%
200/1201.000.50%
250/1251.000.40%
300/1301.000.33%
400/1401.000.25%
500/1501.000.20%
750/1751.000.13%
1000/11001.000.10%
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