American odds — also called moneyline odds — are the standard format at US sportsbooks. Once you understand the two signs and one small piece of arithmetic, every line on the board becomes readable. This guide walks through it with worked examples, then shows how to spot the sportsbook’s margin so you know what you are really being charged.

Minus numbers: favourites

A minus sign marks the favourite. The number tells you how much you must risk to win $100.

At -150, you risk $150 to win $100. If your bet wins, you get $250 back: your $150 stake plus $100 profit. Scale it to any amount — the ratio holds. A $30 bet at -150 wins $20 (30 ÷ 150 × 100), returning $50 total.

The bigger the minus number, the heavier the favourite. -110 is close to a coin flip; -500 means the book sees the outcome as very likely, so you risk $500 to win just $100.

Plus numbers: underdogs

A plus sign marks the underdog. The number tells you the profit on a $100 risk.

At +200, a $100 bet wins $200, returning $300 total. A $25 bet at +200 wins $50, returning $75. The bigger the plus number, the longer the odds and the larger the potential payout relative to your stake.

Converting odds to implied probability

Odds are just probability wearing a payout costume. Converting them back to a percentage tells you what the price is really saying about the chances.

Favourites (minus): implied probability = odds ÷ (odds + 100), using the number without its sign.

For -150: 150 ÷ (150 + 100) = 150 ÷ 250 = 60%. The market is pricing this outcome as a 60% chance.

Underdogs (plus): implied probability = 100 ÷ (odds + 100).

For +200: 100 ÷ (200 + 100) = 100 ÷ 300 = 33.3%. The market sees roughly a one-in-three chance.

You do not need to memorise these. Drop any American price into our odds converter and it returns the implied probability plus the decimal and fractional equivalents. But understanding the maths helps you sanity-check a line at a glance.

Spotting the vig

Here is the part that protects your bankroll. In a fair two-way market, the two implied probabilities would add up to exactly 100%. They never do — the extra is the sportsbook’s built-in margin, called the vig or juice.

Take a typical spread priced -110 on both sides. Each side converts to 110 ÷ (110 + 100) = 52.4%. Add them: 52.4% + 52.4% = 104.8%. That extra 4.8% is the vig. It is why you must win more than half your -110 bets just to break even.

Do the same on any market: convert both sides, add them, and subtract 100. A market that sums to 102% is sharper (cheaper for you) than one that sums to 108%. Our margin calculator does this in one step so you can compare books before you bet. Shopping for lower margins is one of the few edges available to every bettor — and it is completely within your control.

How American odds compare to decimal and fractional

The same price shows up in three costumes around the world:

  • American: +200
  • Decimal: 3.00 (total return per $1 staked, including your stake)
  • Fractional: 2/1 (profit relative to stake)

A quick bridge: decimal odds of 2.00 equal +100 (or -100) — an even-money bet. Anything above 2.00 is an underdog in American terms; anything below is a favourite. If a sportsbook or offshore site shows decimals, the odds converter flips it back to the American format you know.

Putting it to work

Read every line as a probability first. When you see -150, think “60% and I’m paying vig on top.” When you see +200, think “33% chance, decent payout if it lands.” Then check the margin so you know how much the book is skimming.

If you are choosing where to bet, our best betting sites list and full sportsbook reviews flag which operators consistently price at tighter margins — that directly affects your long-run return more than any single pick ever will.

American odds are not complicated once the signs click. Minus is the favourite and shows risk-to-win-$100; plus is the underdog and shows profit-on-$100. Convert to probability, sum the market, and you will always know exactly what the sportsbook is charging you.

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