Calculate the actual odds of horses for Inside Track horse racing in the GTA Online casino.
 

Enter the odds for all 6 horses in the race and hit the Calculate button. If the true odds show in green then the odds are in your favour and you should bet larger amounts. If the true odds are in red then the odds are not in your favour and you should bet the minimum or not bet at all.
The Inside Track: True Odds Calculator is hosted here
 

Fractional odds are a different way of writing the percentage chance the horse will win.
For instance:

• If a horse has 3/1 odds, then the chance of it winning is 25% (100 / (3 + 1)).
• If a horse has EVENS or 1/1 odds, then the chance of it winning is 50% (100 / (1 + 1)).
• If a horse has 19/1 odds, then the chance of it winning is 5% (100 / (19 + 1)).

The fractional odds, when represented as percentages, should all add up to 100%.
For example, when you have a 6 horse race and one horse in this race has odds of EVENS (50%) then the remaining 5 horses will have fractions which add up to 50% between them, for a total 100% overall. It always adds up to 100%, because there is a 100% chance one (and only one) horse will win the race.
 

The odds for horse racing in GTA Online are not calculated the same; as very rarely do the fractions add up to 100%. The odds for the 6 horses in each race are picked randomly (from set pools), which means the total percentage can range from 52.4% to 140.38%. Therefore behind the scenes the odds get adjusted to make it 100%.

Now, in a race where percentages all add up to 100%, when you bet on a EVENS horse there is 50% chance you will win and double your money (for every $1 you put in, you get $1 back). However, in a race where percentages all add up to 75%, the odds for each horse get increased evenly to make it up to 100% total. This means the horse which had EVENS/50% odds actually has a 66.67% chance of winning (to compensate for the missing 25%). The probability of this horse winning has increased a lot, but the money you win does not get adjusted. So the probability of you winning is the same but without you getting a reduced payout if it does, you would still double your money. This is when we want to bet larger amounts, as we have an incresed chance of winning.

In the alternate scenario where all percentages add up to more than 100%, for instance 120%, the opposite is happening; the odds are getting reduced to bring the total back down to 100%. In this scenario the EVENS horse no longer has a 50% chance of winning, it is reduced to 41.67%. This is when we want to bet the absolute minimum because we have a reduced chance of winning (not betting at all would be preferable, but that is only an option in the Main Event).