How to read betting odds: American, decimal, and implied probability
Betting odds express two things at once: how much a winning bet pays, and the win probability the price implies. −110 means risk $110 to win $100 (implied 52.4%); +150 means a $100 bet wins $150 (implied 40%); decimal 2.50 means $2.50 back per $1 staked. Convert any format to a probability and every bet becomes comparable.
Odds look like three different languages depending on where you bet. But they all say the same thing — and once you can convert any price into a probability, you can compare bets across books and formats instantly.
American odds (+150, -200)
A minus number is how much you risk to win $100 (-200 = risk $200 to win $100). A plus number is how much you win on a $100 bet (+150 = win $150 on $100). Minus = favorite, plus = underdog.
Decimal odds (2.50, 1.50)
Decimal is simpler: it's your total return per $1 staked, including your stake. 2.50 means $1 returns $2.50 ($1.50 profit). Multiply your stake by the decimal to get your payout. Many bettors prefer decimal because the math is trivial — and Bankroll Guardian lets you switch the whole app to whichever you like.
Converting to implied probability
Implied probability is the chance the price represents. For decimal odds it's just 1 ÷ decimal (2.50 → 40%). For American, a -200 favorite implies 200 ÷ 300 = 67%, and a +150 dog implies 100 ÷ 250 = 40%. That percentage is the bridge between any two formats.
Why implied probability is the number that matters
Once everything is a probability, betting becomes a simple question: do you think the real chance is higher than the implied chance? If a price implies 40% and you believe it's 45%, that's a value bet. The raw odds are just packaging; the probability is the decision.
One catch: the vig
Add up both sides' implied probabilities and you'll get more than 100% — the extra is the book's margin (the vig). To find the "true" odds you remove it, which is called de-vigging. That's the foundation of finding genuine value, and it's worth its own read.
Fractional odds (5/2, 8/11)
Fractional odds — common in the UK and horse racing — show profit over stake. 5/2 means you win $5 for every $2 you stake, so a $100 bet returns $250 profit — the same as +250 or 2.50 decimal. A fraction smaller than one, like 8/11, is a favorite: you win $8 for every $11 risked. To turn any fraction into decimal, divide and add one (5 ÷ 2 + 1 = 3.50); its implied chance is 1 ÷ 3.50 ≈ 29%.
Bankroll Guardian is a bet-tracking and analytics tool — not a sportsbook, and none of this is betting advice. Betting carries risk; please bet responsibly.