You can learn how do betting odds work in the fractional format involves the use of a simple formula (profit = stake/denominator x numerator). The left side of the odds (numerator) is the profit, while the right side shows the stake (denominator). Accordingly, if you bet $100 at 3/1 (3 to 1), you stand to win $300 in profit. Conversely, if you bet $100 at 1/3 (1 to 3), your profit comes in at $33.33.