An American odds converter takes a price like -150 or +200 and instantly shows you the implied probability — the exact win rate you need to break even — plus the decimal equivalent so you can compare prices across formats.
That is the whole job. Turn a confusing number into a decision number. The chart below does it for every common price you will see on a US sportsbook.
How an American odds converter works
An American odds converter turns a price like -150 or +200 into the implied probability — your break-even win rate — and the decimal equivalent.
What the minus and plus signs mean
The sign is not decoration. It tells you which side is the favorite and which is the underdog.
Minus (-) means favorite. You risk more than you stand to win. -150 means risk $150 to win $100.
Plus (+) means underdog. You risk less than you stand to win. +150 means risk $100 to win $150.
That is it. The rest is arithmetic.
The conversion formulas
There are two formulas. Pick the one that matches the sign.
For negative odds (-N): implied probability equals N divided by (N plus 100). Example: -150 becomes 150 divided by 250 equals 60%.
For positive odds (+N): implied probability equals 100 divided by (N plus 100). Example: +150 becomes 100 divided by 250 equals 40%.
From there, decimal odds are just 1 divided by the implied probability. So 60% implied equals 1 divided by 0.60 equals 1.67 decimal. And 40% implied equals 1 divided by 0.40 equals 2.50 decimal.
Why -110 is the number every spread bettor memorizes
Standard NFL spread juice is -110 on both sides. Convert it: 110 divided by 210 equals 52.38% implied on each side. The two sides sum to 104.76%. That extra 4.76 percentage points is the vig — the sportsbook's margin.
To get the fair, no-vig probability, divide each side by the total: 52.38 divided by 104.76 equals 50% exactly. That is a coin flip, which is what a spread is designed to be. We walk through the full vig-removal math in the vig, juice, and hold explainer.
Real moneyline prices from our odds feed show why conversion matters
We track live moneyline prices across 71 books for NFL games and 10 to 11 books for MLB games. Here is what the board looked like on a recent Sunday.
Packers at Broncos: Denver moneyline -350 to -300 across 71 books . Convert both to implied probability and you see a real difference: -350 implies about 77.8% on Denver, -300 implies 75%. A bettor who shopped got a 2.8-percentage-point edge on implied probability just by picking the right book.
Chiefs at Buccaneers: Tampa Bay moneyline -250 across all 71 books . Zero dispersion — every book agreed. The implied probability is locked at about 71.4% on Tampa Bay. No line shopping edge here, but the converter still tells you the exact break-even rate.
Giants at Dolphins: Miami moneyline +130 to +160 across 71 books . Miami was a +130 dog at some books and a +160 dog at others. That is a massive pricing gap. The implied probability on the Dolphins moneyline swung from about 43.5% to about 38.5% depending on which book you used. Line shopping meaningfully shifted the implied edge.
Ravens at Vikings: Minnesota moneyline -170 to -155 across 71 books . The implied probability on Minnesota ranged from about 63% to about 60.8%. Crossing that gap is worth real expected value. The converter makes that visible instantly.
Commanders at Lions: Detroit moneyline -220 to -140 across 71 books . A wide moneyline range between the highest and lowest offer. That is the difference between Detroit implied at about 68.8% and about 58.3%. If your model says Detroit wins 65% of the time, one book gives you value and the other burns you. The converter is how you know which is which.
The vig hides in the sum — strip it before you decide
Every two-way market sums to more than 100%. That overround is the vig. You cannot evaluate a price until you remove it.
Step 1: Convert both sides to implied probability using the formulas above.
Step 2: Add them. If the total is 104.8%, the vig is 4.8%.
Step 3: Divide each side by the total. That is the fair probability.
We automate this in the odds reader and on the closing line value page so you never have to do the division by hand. But knowing the math means you can spot a bad line in five seconds on your phone.
Decimal odds are easier to think in — switch your app
Decimal odds show total return per $1 staked. 2.50 means a $1 bet returns $2.50 — your $1 back plus $1.50 profit. 1.67 means $1 returns $1.67. The bigger number always pays more. No sign rules, no separate formulas.
Most US sportsbooks let you toggle to decimal in settings. Do it while you learn. The converter above gives you both columns so you can check your work.
Common mistakes the converter prevents
- Thinking +150 means "150% chance." It means 40% implied. The converter makes that instant.
- Ignoring the vig when comparing books. Book A has -105, Book B has -115 on the same side. -105 implies 51.2%, -115 implies 53.5%. That 2.3% gap is free money if you shop.
- Treating heavy favorites as locks. -300 implies 75%. That still loses one in four. The converter reminds you of the real number.
- Chasing big plus numbers. +300 implies 25%. It is only a good bet if the true probability is higher than 25%. The converter is your reality check.
From conversion to edge
Once implied probability is automatic, the rest of the toolkit opens up. Size the bet with the Kelly criterion. Track whether you beat the closing line with closing line value. Keep the bankroll intact with basic bankroll management.
Start now: pull up any game on the odds guide, convert both sides in your head, and check against the chart above. After a few dozen reps the math becomes automatic. You will never look at a betting line the same way again.
What would change our mind
If a sportsbook posted a two-way market that summed to exactly 100% with no vig — we would stop teaching the conversion and start betting every side. Until then, the converter is the first line of defense against overpaying.
Bet responsibly — set limits, never chase losses.
Expected bankroll growth at 55% edge
Expected geometric growth of a $100 bankroll under different Kelly multipliers across 1000 bets at p=0.55, decimal=2. Full Kelly maximises long-run growth but produces the deepest drawdowns; fractional Kelly trades growth for variance.
EV per $100 across win rate × odds grid
Expected value of a $100 stake at each combination of true win rate and market odds. Anywhere the cell is positive you have a long-run profitable bet; the magnitude shows how aggressive Kelly will size it.
