To consider oneself a serious punter and not know how to “decode” the numbers behind odds is totally incompatible. Before placing a bet, one must understand the three main kinds of odds and learn to use them correctly. Otherwise, it’s just like spending money to passively pass the time, when there are far more entertaining and inexpensive ways to do so…. Fortunately, understanding the numbers behind odds is a simple task which we will try to explain below.
The 3 main categories are decimal odds, fractional and American. Each name suggests the way in which we see them written. Depending on where and what sport we bet, sometimes it is easier to use a different type, although most of us more or less tend to use always the same category.
The most popular category, which is mostly used in Europe, is decimal odds and of course it is offered as an option at any serious bookmaker worldwide. The number of the odds represents how much money you win if you bet 1 unit. Most bookmakers offer odds of 2 decimal places for greater accuracy. For example, if an odd is 2.15, this means that if you bet and win the bet, you will receive 2.15 times the money you bet. If for example you bet 50 euros, you get 50×2.15 = 107.5 euros. Our net profit in this example will be 107.5-50=57.5 euros.
The second most popular category is fractional odds, that are used mainly in the UK. The odds more or less follow the same idea as with decimal units, but express a different meaning. Fractional odds show the player his net gain when he bets a unit and not the total amount to be received as the decimal. For example, the corresponding value for odds 2.15 seen previously will be 23/20 which means that if you make a 20 euro bet, you will earn net profit of EUR 23.
American odds are a different situation. They are based on a percentage scale, giving a positive or a negative result. If the odds are positive, they shows us our net profit based on a bet of one hundred euros/dollars/GBP (eg, 115 means that if you bet 100 euros/dollars/GBP and you win, you will have a net profit of 115 and total return 100+115 = 215). Otherwise, when the odds are negative, they shows us how much you must bet to win 100 euros (for example -110 means that in order to win 110 you have to bet 100, so the total return will be 110+100=210 euros/dollars/GBP or any other currency used.
Decimal odds are easier to use and for this reason they are used more around the world, but the understanding of all other types is also not so difficult. The following table lists the corresponding odds for all three categories in order to make comparisons easier:
| Decimal Odds | Fractional Odds | American Odds |
| 1.01 | 1/100 | -10000 |
| 1.10 | 1/10 | -1000 |
| 1.40 | 2/5 | -250 |
| 1.50 | 1/2 | -200 |
| 2.00 | 1/1 | (-)100 |
| 3.00 | 2/1 | 200 |
| 5.00 | 4/1 | 400 |
| 10.00 | 9/1 | 900 |
| 101.00 | 100/1 | 10000 |