If you’re new to sports betting — or even if you’ve placed a few bets and still feel a little foggy on what the numbers actually mean — this is the guide you need. Understanding how odds work isn’t just academic. It’s the foundation of making smart bets instead of just guessing.
What Are American Odds?
In the US, odds are displayed in what’s called the American format — a number with a plus (+) or minus (–) sign in front of it. That sign tells you everything.
The Plus Side: Underdogs
A +150 means you bet $100 to win $150. The plus sign always tells you your profit on a $100 bet. Simple.
The Minus Side: Favorites
A -150 means you need to bet $150 to win $100. The minus sign tells you how much you need to risk to profit $100. The bigger the number, the bigger the favorite — and the more you’re laying down to win less.
Quick example: -200 means you bet $200 to win $100. +200 means you bet $100 to win $200. Keep that relationship in your head and American odds will click immediately.
Point Spreads: Betting Beyond Win/Loss
A moneyline is just picking a winner. But a point spread introduces a margin. The sportsbook handicaps the favorite to make both sides attractive to bettors.
Let’s say you’re betting on a game in the NFL:
- Team A -3.5 (favorite)
- Team B +3.5 (underdog)
If you bet on Team A -3.5, they need to win by 4 or more points for you to win. If you bet Team B +3.5, they can lose by up to 3 points and you still cash. Spreads are the most popular bet type in football and basketball — you’ll see them everywhere from the NBA to college hoops.
The half-point (.5) eliminates pushes (ties). A spread of exactly -3 with no half-point means if Team A wins by exactly 3, everyone gets their money back — that’s a push.
Totals (Over/Under): Betting on the Score
A total — also called the over/under — is a number the sportsbook sets for the combined score of both teams. You bet whether the actual total will be higher (over) or lower (under).
Example: The total for tonight’s NHL game is set at 5.5. If you take the over, you need both teams to combine for 6+ goals. Under means 5 or fewer total goals.
Totals are huge in MLB betting, where run environments vary wildly depending on the pitching matchup, ballpark, and weather. A windy day at Wrigley can swing a total by 1.5 runs.
Implied Probability: What Odds Actually Mean
Odds aren’t just about how much you win — they reflect how likely the sportsbook thinks an outcome is. That’s called implied probability. Here’s how to convert:
For Negative Odds (Favorites)
Implied probability = |odds| ÷ (|odds| + 100)
-150 → 150 ÷ 250 = 60%
For Positive Odds (Underdogs)
Implied probability = 100 ÷ (odds + 100)
+150 → 100 ÷ 250 = 40%
Why does this matter? Because if you think a team has a 55% chance of winning but the odds only imply 45%, you have an edge. That’s the whole game — finding spots where your estimate is better than the sportsbook’s.
Practical Tips: Shopping Lines and Closing Line Value
Shop Your Lines
Different sportsbooks will often have slightly different odds on the same game. If one book has Team A at -110 and another has them at -105 — that’s real money over hundreds of bets. Always have at least 2–3 books and compare before placing.
What Is Closing Line Value (CLV)?
Closing line value is whether the odds you bet at were better than the final line when the game started. Sharp bettors — the ones who actually beat the books long-term — consistently bet lines before they move against them. If you’re regularly getting +120 on sides that close at +105, that’s a good sign you’re finding value. CLV isn’t perfect, but it’s one of the few objective benchmarks for betting quality over time.
Bottom Line
Reading odds is a skill that compounds. Once moneylines click, spreads make sense. Once spreads click, totals and implied probability follow naturally. The whole point is to go from “I like this team” to “I think this line is off and here’s why.” That shift in thinking is what separates recreational bettors from consistent ones.