How do I read horse racing odds when I bet?

At most
bookies, horse racing odds are shown in decimal format. That indicates that the
number you see will show how much cash you’ll have if you win the bet, which
includes your original wager. For example, if you bet $1 at 3.00 odds, winning
will imply you now have $3 – your original dollar, and the $2 you have won.

There
are some other ways that horse race odds are shown around the world, but most
on-line betting sites will permit you to use quebrado odds or any other major
technique you prefer. One unusual process that should be described is the
method used to show payouts in the United States. This method is related to
decimal odds, but that assumes a $2 bet at all times. After a race, you may see
that a successful horse paid $6.00. That figure is based on a $2 bet;
basically, this is the same as 3.00 in decimal odds. 

The main types of odds are:

Decimal Odds, Fractional Odds, American Odds

It is best that you find which type makes most sense for you, and most online bookmakers and betting exchanges will have settings where you can choose the type you prefer.

Personally I prefer Decimal Odds. The way that decimal odds works is as follows:

For Decimal: 3.00 odds means that for every dollar you bet, if your bet wins you get 3x the amount back. So if you bet $200, if it wins you get a return of $600.

Fractional Odds are shown as a fraction. E.g. 2/1

The simplest way of looking at this is that, the right hand side is equivalent to the bet amount, and the left hand side is the profit. In the example above of 2/1 for every $1 you bet, you get $2 of profit (total return is $3). So its the same as the decimal bet, just shown in a different way. This is a popular way to display odds in UK.

American Odds, the example above would be shown as a +200. For every $1 you bet, you get a profit of $2. If you were to bet on a heavy favorite, e.g. 1.10 decimal odds, it would be shown as -1,000 in American Odds.

You can also find odds converter websites online, simply go on google and type in 'odds converter' and you can enter in the odds and sites will have a tool to show you the odds in whatever type you prefer.