Stop Guessing, Start Reading: Decode American Odds Before Kickoff
Photo: Dick Thomas Johnson from Tokyo, Japan, CC BY 2.0, via Wikimedia Commons
Ever stared at a sportsbook screen and wondered why one team has a minus sign and the other has a plus? You're not alone. Every Sunday, millions of Americans open their betting apps, see numbers like -135 and +220, and make decisions based on gut feel alone. Here at OnBet66, we think the numbers should work for you, not confuse you. Let's crack the code together.
What Those Plus and Minus Signs Actually Mean
American odds are built around one simple benchmark: $100. That's it. Everything on the board is anchored to a Benjamin.
The minus sign (-) tells you the favorite. The number shows how much cash you need to risk to win $100. So if the Chiefs are -150, you'd wager $150 to pocket a $100 profit. The bigger the number, the heavier the favorite — a -300 line means the market really believes in that team.
The plus sign (+) tells you the underdog. Here the number shows how much you'd win on a $100 bet. An underdog at +220 means a $100 stake returns $220 in profit if they pull off the upset. Bigger plus number, bigger payout, bigger long shot.
Quick example from an NFL Sunday:
- Bills -140 vs. Jets +120
Bet $140 on Buffalo to win $100. Or throw $100 on New York and collect $120 if they shock everyone at MetLife Stadium. Both bets risk what you put up — the difference is just how the sportsbook prices each side.
Implied Probability: The Number Behind the Number
Here's where casual bettors separate from sharp ones. Every odds line hides a percentage — the sportsbook's estimate of how likely that outcome is. It's called implied probability, and converting it takes about ten seconds.
For favorites (minus odds):
Implied probability = odds ÷ (odds + 100)
So -200 becomes 200 ÷ 300 = 66.7%. (Yes, 66 — the universe is telling you something.)
For underdogs (plus odds):
Implied probability = 100 ÷ (odds + 100)
So +150 becomes 100 ÷ 250 = 40%.
Why does this matter? Because once you can translate odds into percentages, you can start asking the only question that matters in sports betting: do I think this team's real chance of winning is higher than what the book is charging?
Spotting Value: Where the Money Is Actually Made
A value bet isn't a bet on the team you think will win. It's a bet where your assessment of the probability beats the implied probability in the odds.
Say the Celtics are priced at -160 against the Heat. That's an implied probability of about 61.5%. If your research — injuries, rest, home court, recent form — tells you Boston wins this matchup closer to 70% of the time, you've found value. The sportsbook is undercharging you for a likely outcome.
Flip it around: an MLB moneyline with the Rockies at +180 implies roughly 35.7%. Even if you like Colorado's chances at Coors Field, you need to genuinely believe they win more than 36% of the time to make that bet worthwhile. Most bettors never do this math. The ones who do last a lot longer.
Moneylines vs. Spreads: Two Different Animals
Moneylines are straightforward — pick the winner. Spreads add a handicap to level the playing field.
When the Lakers are -5.5 against the Kings, they don't just need to win; they need to win by 6 or more for your bet to cash. Sacramento at +5.5 covers even in a tight 3-point loss. Spread prices are usually near -110 on both sides, meaning you risk $110 to win $100 either way. The odds reading skills you just learned still apply — it's the same minus/plus logic, just attached to a margin instead of a winner.
Your Game Day Cheat Sheet
Print this out, screenshot it, tape it to your second monitor. These are the conversions worth memorizing:
| Odds | Implied Probability | $100 Bet Pays |
|---|---|---|
| -300 | 75.0% | $33.33 |
| -200 | 66.7% | $50.00 |
| -150 | 60.0% | $66.67 |
| -110 | 52.4% | $90.91 |
| +100 | 50.0% | $100.00 |
| +150 | 40.0% | $150.00 |
| +200 | 33.3% | $200.00 |
| +300 | 25.0% | $300.00 |
Three rules of thumb to go with it:
- Favorites around -110 to -150 are near coin flips with a slight lean — proceed with confidence, not certainty.
- Anything past -250 means you're risking a lot to win a little. One upset ruins your week.
- Underdogs above +200 are lottery tickets. Small stakes only, unless you've got a genuine edge.
The Rookie Mistakes to Avoid
Even with the math down, newcomers trip over the same rocks. Don't blindly back big favorites — the juice eats you alive over a season. Don't ignore line movement; a number shifting from -3 to -4.5 tells you where sharp money is going. And never bet a game you haven't priced yourself. If you can't attach a rough win probability to a team, you're not betting — you're guessing with extra steps.
The bottom line? Odds are just a language, and now you speak it. The next time you open the board on a Friday night, those plus and minus signs won't look like noise. They'll look like prices — and you'll know exactly when something's on sale.
