Decoding "reading decimal odds" 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 exactly the same.
Hear it instead
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 racing counters.
Decimal odds are the simplest format for reading a price. The number is the whole return for one unit, stake included, so 2.50 returns two and a half units and the profit is 1.50. The decimal odds formula is just payout equals stake times odds, simple enough to need no calculator. Evens in decimal odds is 2.00, where the profit matches the stake. Decimal odds can never be negative or fall below 1.00, because the return always includes the stake, and most sports betting quotes prices this way.
Fractional odds set profit against stake, so 5/2 pays five units of profit for every two staked, with the stake returned on top.
Evens is 2.00 in decimal notation, the price at which a winning bet's profit exactly matches the amount staked.
A figure such as minus 200 shows the stake needed to win one hundred, which is why a favourite always carries a negative number.
A figure such as +150 shows the profit on a stake of one hundred, and a positive number marks the underdog in the market.
One over the price: 4.00 points to twenty five per cent, and fractional or American prices convert through the same route.