Fractional odds are expressed as a fraction and are commonly used in the UK, often for horse racing, such as 4/1 or 7/20.
The number to the left of the slash is how many times the outcome is expected to fail. The number on the right shows how many times the outcome is expected to succeed. The underdog typically has a higher number on the left, the favourite a higher number on the right.
To calculate potential winnings, multiply your wager by the quotient, or the result of dividing the fraction.
For example, odds of 4/1 ("four-to-one") mean you stand to make a $4 profit on a $1 bet. If the odds are 1/4 ("one-to-four"), you stand to make $0.25 on a $1 bet.
In either case, should you win, you always receive your original stake back, so if the odds are 4/1 and you wagered $100 you receive a total payout of $500 ($400 winnings plus the original $100 bet).