How to read American odds and implied probability
Negative odds show how much you bet to win 100 (-150: bet 150 to win 100). Positive odds show how much 100 wins (+130: bet 100 to win 130). The implied chance of -150 is 60%; of +130, about 43.5%.
The formulas
Negative odds: chance = odds ÷ (odds + 100), using the number without the minus. -150 → 150 ÷ 250 = 60%.
Positive odds: chance = 100 ÷ (odds + 100). +130 → 100 ÷ 230 = 43.5%.
Decimal odds: negative → 1 + 100 ÷ odds (−150 → 1.67); positive → 1 + odds ÷ 100 (+130 → 2.30).
Break-even
The implied chance is also the win rate you need to break even at that price over many bets. At -110 that is 52.4%.
Parlays
Multiply the decimal odds of each leg. Two legs at -110 (1.909 each) make 3.64, or about +264.
Questions
What does -110 mean?
Bet 110 to win 100. It implies a 52.4% chance, which is the break-even win rate at that price.
Is + or - odds the favourite?
The minus side is the favourite. The bigger the minus number, the bigger the favourite.