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 the same.
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 it is negative.
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.
Evens is 2.00 in decimal notation, the price at which a winning bet's profit exactly matches the amount staked.
Seeing the same number as decimal and as American or fractional catches misreadings, since any format can express the price and its chance.
No. Converting between decimal, fractional and American notation changes only how the number looks; the probability and the margin stay identical.
Fractional odds set profit against stake, so 5/2 pays five units of profit for every two staked, with the stake returned on top.