Calculator
Betting odds calculator
Type a price in any format — American, decimal or fractional — and a stake. You get every other format back, the implied probability, and exactly what the bet pays.
American
−110
Decimal
1.909
Fractional
10/11
Implied probability
52.38%
Profit if it wins
$90.91
Total payout
$190.91
Three ways of writing the same price
American, decimal and fractional odds are not three different prices — they are three notations for one price, and every one of them encodes the same two things: how much a winning bet returns, and what the book thinks the chances are. Converting between them is arithmetic, not interpretation, so if two formats ever seem to disagree, one of them has been copied down wrong.
American odds
The default at US sportsbooks. A negative number is the favourite: −150 means you risk $150 to win $100. A positive number is the underdog: +150 means you risk $100 to win $150. The anchor is always $100, which is why the negative side looks "upside down" — it is quoting the risk, not the win.
Decimal odds
Standard everywhere outside the US, and the format every betting exchange uses. Decimal is the total return per unit staked, stake included: 2.50 returns $2.50 for every $1, which is $1.50 of profit. Implied probability is just 1 ÷ decimal, which is why sharp bettors and every model on this site do their thinking in decimal and only translate back for display.
Fractional odds
The format of horse racing and UK bookmakers. 7/2 pays $7 of profit for every $2 staked. Fractional quotes profit only — your stake comes back on top — which is the single most common source of confusion when Americans read a tote board or a futures sheet. A horse at 2/1 is not "a 50 percent shot"; it is 1 ÷ (2 + 1), or 33.3 percent, before the track's takeout.
Implied probability is the point of all of it
Every price is a probability wearing a costume. −110, 1.91 and 10/11 all say the same thing: about 52.4 percent. That is the number worth remembering, because it is the one you compare against your own estimate. If you think a side wins 55 percent of the time and the price implies 52.4, you have a bet. If you think 51, you don't — no matter how much you like the team. And remember that a book's two sides always sum to more than 100 percent; the surplus is the vig, which you can strip out with the no-vig calculator before making that comparison.
Quick reference
+100 = 2.00 = 1/1 (evens) = 50%. −110 = 1.91 = 10/11 = 52.4%. −150 = 1.67 = 2/3 = 60%. +200 = 3.00 = 2/1 = 33.3%. −200 = 1.50 = 1/2 = 66.7%. +400 = 5.00 = 4/1 = 20%. Learn those six and you can translate any board in your head.