They are three ways to write the same price. American odds sit around 100 with a plus or minus (+150, -110). Decimal odds show your total return per unit staked (2.50). Fractional odds show profit relative to stake (3/2). All three imply the same probability.

If the decimal is 2.00 or higher, subtract 1 and multiply by 100, so 2.50 becomes +150. If it is below 2.00, divide -100 by the decimal minus 1, so 1.50 becomes -200. The converter above does it instantly.

+150 means a $100 winning bet profits $150, for a total return of $250. Positive American odds always show the profit on a $100 stake. The price implies about a 40% chance.

-110 means you risk $110 to profit $100, the standard price on a point spread. Negative odds show how much you must stake to win $100. It implies about a 52.4% break-even rate.

Convert the price to decimal and divide 1 by it. For 2.50 decimal, 1 divided by 2.50 is 40%. Beating that break-even number over time is the whole game.