Reading betting lines
American, decimal, and fractional odds explained from first principles. How to read a moneyline, a spread, and a total without memorizing tables.
Three odds formats are in common use. They look different. They mean the same thing. Once you can convert between them in your head, every line on every sportsbook becomes a quoted probability with a markup.
American odds
The default in the United States. A line of -110 means you risk 110 to win 100. A line of +150 means you risk 100 to win 150. The number is a ratio expressed against a 100-unit stake on one side or a 100-unit win on the other.
BET SIDE A AT -120 RISK $120 TO WIN $100 PAYOUT $220 (stake + profit) BET SIDE B AT +180 RISK $100 TO WIN $180 PAYOUT $280 (stake + profit)
The convention: a minus sign in front of the number means the side is favored (you risk more than you win). A plus sign means the side is the underdog (you win more than you risk).
Decimal odds
Standard outside the United States and used by most modeling platforms because the math is cleaner. The decimal is the multiplier on your stake including the stake. A line of 1.91 means each $1 you risk returns $1.91 if you win. The profit is $0.91. The stake is the same $1 either way.
DECIMAL ODDS 1.91 $100 STAKE × 1.91 = $191 RETURNED PROFIT $91 DECIMAL ODDS 2.50 $100 STAKE × 2.50 = $250 RETURNED PROFIT $150
Decimal odds are usually quoted to two decimal places. The implied probability is simply 1 divided by the decimal price.
Fractional odds
The traditional UK format. Fractional odds express the profit relative to the stake as a fraction. A line of 5/2 (read as five to two) means a $2 stake returns $5 in profit, plus your stake back. A line of 1/4 means a $4 stake returns $1 in profit.
Converting between formats
You do not need to memorize a table. Two formulas cover all three formats.
AMERICAN → DECIMAL if odds < 0: decimal = 1 + (100 / |odds|) if odds > 0: decimal = 1 + (odds / 100) DECIMAL → IMPLIED PROBABILITY prob = 1 / decimal EXAMPLES -120 → 1 + 100/120 = 1.833 → 54.5% implied +180 → 1 + 180/100 = 2.800 → 35.7% implied -110 → 1 + 100/110 = 1.909 → 52.4% implied
The implied probability converter does this for you and shows the book's hold on a two-sided market. A reader who works through this article once should be able to read American odds at a glance and convert to implied probability without the tool.
Implied Probability
// WB://TOOLS/IMPLIED-PROBConversions
Probability and hold
Two-sided market. Total implied probability over 100% indicates the book's hold. Fair probability re-normalizes to 100%.
How to read a moneyline
A moneyline is a price on which side wins, straight up. No spread, no total. Read it as the cost of a winner and the payout on a winner.
| Team | American odds | Decimal | Implied prob |
|---|---|---|---|
| Yankees | -145 | 1.69 | 59.2% |
| Red Sox | +125 | 2.25 | 44.4% |
The two implied probabilities sum to 103.6%, not 100%. The 3.6 percentage points above 100 are the book's hold. That excess is the price the bettor pays for the privilege of accessing the market on either side.
How to read a spread
A spread (sometimes called the line, the handicap, or the points) is a number applied to the final score. The favorite gives points; the underdog gets points. The bet pays based on whether the favorite wins by more than the spread or the underdog stays within the spread (or wins outright).
| Team | Spread | Price |
|---|---|---|
| Chiefs | -3.5 | -110 |
| Bills | +3.5 | -110 |
If you bet the Chiefs at -3.5, the Chiefs must win by 4 or more for your bet to win. If you bet the Bills at +3.5, the Bills must lose by 3 or fewer (or win) for your bet to win. The price next to the spread is a separate line on its own. -110 on each side means the book is taking 4.5% hold on a balanced spread market.
How to read a total
The total is a number representing the book's expectation of the combined score of both teams. You bet over (the actual combined score will be higher than the number) or under (the combined score will be lower).
| Total | Price |
|---|---|
| Over 224.5 | -110 |
| Under 224.5 | -110 |
Pricing on totals works the same as spreads. Equal money on each side at -110 nets the book ~4.5% hold. Pricing also moves in response to expected pace, weather (in baseball and football), pitching matchups (in baseball), or rest (in basketball).
What to read next
Once you can read odds, the natural next step is the bet types beyond moneyline, spread, and total: bet types explained. To go deeper on what the implied probability tells you about the bet's value, work through expected value.