Decoding "How odds work in betting?" starts with notation. Betting odds come in three formats that say the same thing in different ways. Decimal odds show the total return per unit staked, American odds show a win on a hundred or the stake needed to win a hundred, and fractional odds show profit against stake. What changes between them is the notation; the price and the margin inside it stay the same.
Decimal odds vs American odds is a question of habit more than value. Both describe the same probability and the same margin, so neither format pays more. The case for why decimal odds are better is practical: the return is visible at once, comparing two prices needs no sign rules, and multiplying the legs of a combination bet works directly. American odds suit anyone who thinks in wins per hundred, and fractional odds still appear at the racing counter.
Converting between the formats takes one step each. Fractional to decimal odds means dividing the fraction and adding one, so 5/2 becomes 3.50. American odds to decimal works the same way: a positive number is divided by one hundred and one is added, and for a negative number one hundred is divided by the number, ignoring its sign, before adding one. Decimal odds to American odds reverses the path: above 2.00, subtract one and multiply by one hundred.
American odds work from a base of one hundred. A positive number, such as +150, shows the profit on a stake of one hundred, so positive betting odds mean the pick is the underdog. A negative number, such as -200, shows the stake needed to win one hundred, which is why betting odds are negative on a favourite. The American odds formula for profit is stake times the number over one hundred when it is positive, and stake times one hundred over the number when negative.
No. Converting between decimal, fractional and American notation changes only how the number looks; the probability and the margin stay identical.
Evens is 2.00 in decimal notation, the price at which a winning bet's profit exactly matches the amount staked.
Fractional odds set profit against stake, so 5/2 pays five units of profit for every two staked, with the stake returned on top.
A figure such as +150 shows the profit on a stake of one hundred, and a positive number marks the underdog in the market.
The whole return for one unit staked, stake included, so a price of 2.50 returns two and a half units, of which 1.50 is profit.