# Decimal Betting Odds

June 20, 2011

Odds are probably the most important numbers to understand in sports betting since they indicate how much money a bet can win and how likely an outcome is. Historically several systems of quoting odds have developed in different parts of the world. The three most prominent of them are fractional, decimal and moneyline or American odds.

### Why Decimal Odds?

In Betfair (and thus in matched betting) decimal odds are used because they are precise, easy to understand and easy to make calculations with. If you are new to sports betting, don’t bother with other types of odds but use the decimal ones.

If you are used to another system of quoting odds, you will need to convert them to decimal odds to use Betfair and to make money  as described in our matched betting guide. When you are using bookies, make sure to choose decimal odds to be displayed to avoid confusion in matched betting.

### Understanding Decimal Odds

As I mentioned before, decimal odds are easy to do calculations with. If you place a back bet that wins, you will have your initial stake multiplied by the odds after the bet; if your back bet loses, you lose the amount of your bet. An example: If the odds for Fortuna to win are 2.8 and you place a £10 back bet, you can profit £18 and get your initial £10 stake back if Fortuna wins, which means that you will have £28 together.

If Fortuna loses, you lose our stake. After a successful back bet your bank equals stake multiplied by odds; to calculate your profits you have to subtract your initial profits from this number (or simply let Betfair do the job for you).

If you place a lay bet at the same odds, the amount of money that you would risk on a back bet (your stake) becomes your potential profit, while the potential profit of a back bet becomes the money you risk or your liability. Basically a lay bet is the exact opposite of a back bet – whenever you back a selection on Betfair there is someone laying it and vice versa.

The same example from a laying perspective: A £10 lay bet wins £10 (regardless of the odds) if the selection doesn’t win, but loses its liability (£18 at the odds of 2.8) if the selection wins. The profit of a lay bet always equals your initial stake, meaning that you double it if the selection doesn’t win. The liability you lose if a selection wins equals your stake multiplied by the odds minus your stake (£10*2.8-£10).

Another benefit of decimal odds is that their reciprocal (1/odds) equals the implied probability of an outcome. In the example above the likelihood of Fortuna winning is 35.71% (1/2.8), assuming that the odds are accurate.

Do I Really Have to Understand all These Confusing Numbers?

While it is good if you do understand them, you can still use Betfair if you don’t because it automatically does all these calculations for you. To enable them check Display “what if” figure in Profit and Loss Display section that can be found by clicking on More Options button on the top of any betting market. If Display P&L net of commission is checked, it will also take into account Betfair commission. Just remember that back bets are always blue unlike lay bets that are pink. ### Converting to Decimal Odds

If you ever need to convert fractional odds to decimal ones, do the division and add 1. For example, 9/5 equals 2.8 in decimal odds (9/5=1.8, 1.8+1=2.8).

To convert negative moneyline odds get rid of the negative symbol, take 100 and divide it by the moneyline amount, then add 1. For example, -200 is 1.50 in decimal odds (-200à200 100/200=0.5 0.5+1=1.5)

To do that with positive moneyline odds divide them by 100 and add 1. 180 equals 2.8 (180/100+1=2.8).

Luckily, you don’t have to perform all these complicated calculations yourself – there is a handy converter on the right side of the Betfair screen.

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