American Odds vs Decimal Odds: How to Convert and Compare

Open a US sportsbook and you’ll see odds like -110 or +140. Open Kalshi, a betting exchange, or most sportsbooks outside the US and you’ll see the same bet priced as 1.91 or 2.40. Same bet, same risk, same payout – just written in a different language. If you’re comparing prices across platforms to find value, and you can’t translate between the two formats in your head, you’re going to misjudge which side is actually offering the better number.

That mistranslation is an easy way to leave edge on the table. Here’s how the two formats work, how to convert between them, and why it matters more than it looks like it should.

The short answer

American odds tell you either how much you’d win on a $100 bet (positive numbers, like +140) or how much you’d need to risk to win $100 (negative numbers, like -110). Decimal odds tell you your total payout – stake included – for every $1 wagered. A decimal odds of 2.40 means a $1 bet returns $2.40 total if it wins: your original dollar plus $1.40 in profit.

They’re two different ways of expressing the exact same implied probability. Neither format is “better” – American is the US sportsbook standard, decimal is the standard almost everywhere else, including most betting exchanges and prediction markets. If you’re pricing a bet against a Kalshi contract or a European book, you need to convert one of them before you can compare apples to apples.

Converting American odds to decimal

For positive American odds, the formula is:

decimal = (American odds / 100) + 1

For negative American odds, the formula is:

decimal = (100 / absolute value of American odds) + 1

Worked example: a moneyline sitting at +140 converts to (140 / 100) + 1 = 2.40. A moneyline at -110 converts to (100 / 110) + 1 = 1.91.

Notice the “+1” in both formulas. That’s the stake being added back in. American odds show you profit; decimal odds show you total return. Forgetting that +1 is the single most common conversion mistake, and it’ll make every decimal numbers you calculate look artificially low.

Converting decimal odds to American

Going the other direction, the rule depends on whether the decimal odds are 2.00 or higher.

If decimal odds are 2.00 or higher: American odds = (decimal odds – 1) x 100

If decimal odds are below 2.00: American odds = -100 / (decimal odds – 1)

Worked example: decimal odds of 2.40 convert to (2.40 – 1) x 100 = +140. Decimal odds of 1.91 convert to -100 / (1.91 – 1) = -109.9, which rounds to -110 – matching the American number we started with above.

That 2.00 threshold matters because it’s the break-even point. Decimal odds of 2.00 mean even money – risk $1 to win $1 profit, identical to +100 in American terms. Above 2.00, you’re getting paid more than you risk (underdog pricing). Below 2.00, you’re risking more than you stand to win (favorite pricing).

Where you’ll actually run into both formats

American odds are the default on every US-facing sportsbook – DraftKings, FanDuel, BetMGM, Caesars, all of it. That’s the format most US bettors learn first, and it’s the one built into most bet slips and same-game parlay calculators.

Decimal odds show up in three places that matter for +EV bettors specifically. First, prediction market exchanges like Kalshi quote contracts in cents on the dollar, which converts cleanly to decimal math since a contract price is just an implied probability times 100. Second, most odds-comparison and line-shopping tools default to decimal because it’s easier to do implied-probability math on without a sign flip for favorites versus underdogs. Third, if you ever bet through an offshore or international book, decimal is the house format there too.

The practical result: the moment you start comparing a US sportsbook line against a Kalshi-anchored fair value line, or against any third-party odds tool, you’re crossing formats whether you notice it or not. That’s the exact situation where a silent conversion error turns into a real bankroll mistake.

Common mistakes that cost real money

Two errors show up constantly, and both are conversion errors, not judgment errors.

The first is comparing raw numbers across formats without converting either one – treating a decimal 1.91 as “worse” than an American +140 just because 1.91 is a smaller number on the page. They can’t be compared directly; only their implied probabilities can.

The second is forgetting that decimal odds already include the stake and American odds don’t. Bettors who mentally treat decimal 2.40 as “$2.40 profit on a $1 bet” instead of “$2.40 total return, $1.40 of it profit” will consistently overestimate how much a decimal-quoted bet actually pays – which throws off any expected-value calculation built on top of it.

Why this matters for +EV betting

Positive expected value betting is about comparing a bet’s true probability of winning against the price you’re being offered, then betting when the price is better than the true odds justify. That comparison only works if every price is in the same units.

If you’re checking a sportsbook’s -115 against a Kalshi contract trading at 47 cents, or against a fair-value line quoted as 1.87 in decimal, you can’t eyeball which number is better. -115 doesn’t look “bigger” or “smaller” than 1.87 in any intuitive way – you have to convert both into implied probability first. -115 implies roughly 53.5% (115 / 215). Decimal odds of 1.87 imply roughly 53.5% too (1 / 1.87). Once you convert, you can see instantly whether they actually match, or whether one side is pricing the outcome differently than the other – which is exactly where a betting edge tends to show up.

Skip the conversion step, or do it wrong under time pressure before a line moves, and you’ll either miss a real edge or think you found one that isn’t there. Small formula errors compound the same way small pricing errors do: they don’t show up on any single bet, they show up in your long-run results.

A quick sanity check you can run in your head

You don’t need to memorize both formulas perfectly to avoid the worst mistakes. Two quick checks catch most errors:

Decimal odds should never be below 1.00 – if your conversion produces that, you made a sign error. And decimal odds of exactly 2.00 should always convert back to +100, never -100 or +99 – that’s your anchor point for checking whether a formula was applied correctly in either direction.

How Automatehive Edge handles this

Edge prices every +EV alert against a fair-value line anchored to Kalshi’s exchange pricing, then compares it to the sportsbook’s posted number – automatically, in the background, before you ever see the alert. You’re not asked to convert formats or do implied-probability math under time pressure while a line is moving. The comparison Edge shows you is already normalized, so what you’re looking at is the actual gap between the sportsbook’s price and the fair-value benchmark, not a formatting artifact that looks like a gap but isn’t one.

That matters because the biggest hidden cost in manual odds-shopping isn’t missing value – it’s misreading value that was never really there, because two numbers in different formats happened to look far apart when they were actually close, or vice versa.

The takeaway

American and decimal odds are just two dialects for the same underlying probability. Converting between them is simple arithmetic, but doing it correctly and consistently, especially under the time pressure of a moving line, is where most manual odds comparisons quietly go wrong. Know the formulas, check your work against the 2.00 = +100 anchor point, and don’t compare prices across formats until you’ve converted them into the same language.

If you’d rather skip the mental math entirely, that’s exactly what automated fair-value comparison is for. See how it works at automatehive.net/edge.

Not betting advice. Bettors must be 21+. Bet responsibly — only wager what you can afford to lose. Gambling problem? Call 1-800-GAMBLER.