What Are Betting Odds?
Betting odds serve two purposes at once: they tell you how likely a sportsbook believes an outcome is, and they tell you how much you'll be paid if you're right.
A common misconception is that odds represent a sportsbook's prediction. They don't — not exactly. Odds are a pricing mechanism designed to attract roughly balanced action on both sides of a market while building in a profit margin for the house. The implied probability is real, but the primary job of the line-setter is risk management, not forecasting.
There are three main formats for expressing odds: American, decimal, and fractional. They convey the same information in three different languages.
American Odds Explained
American odds — also called moneyline odds — are the standard format at US sportsbooks. They're built around a $100 reference point, though you don't need to bet exactly $100.
Negative odds (favorites)
A minus sign indicates the favorite. The number shows how much you must risk to win $100 in profit.
Example: −150
- Bet $150 to win $100 profit
- Total payout if you win: $250 ($150 returned + $100 profit)
The larger the negative number, the heavier the favorite — and the lower the return relative to risk.
Positive odds (underdogs)
A plus sign indicates the underdog. The number shows how much profit you earn on a $100 bet.
Example: +200
- Bet $100 to win $200 profit
- Total payout if you win: $300 ($100 returned + $200 profit)
Odds quick-reference
| Odds | Implied probability | Profit on $100 bet |
|---|---|---|
| −300 | 75.0% | $33.33 |
| −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 |
| +500 | 16.7% | $500.00 |
Implied Probability: Converting Odds to a Win Percentage
Implied probability converts odds into the win percentage they represent — how often a bet needs to win for you to break even.
Negative odds: |Odds| ÷ (|Odds| + 100) × 100
→ −150: 150 ÷ 250 × 100 = 60.0%
Positive odds: 100 ÷ (Odds + 100) × 100
→ +200: 100 ÷ 300 × 100 = 33.3%
Add up the implied probabilities for both sides of any bet and they'll sum to more than 100%. That excess is the vig — the sportsbook's built-in margin. At standard −110/−110 both sides = 52.4%, totalling 104.8%. The extra 4.8% goes to the house regardless of which side wins.
This means you need 52.4% wins at −110 just to break even — not 50%.
What Is the Vig?
The vig (vigorish), also called juice or overround, is the sportsbook's commission embedded directly into every line.
Vig by market type
| Bet type | Typical vig | Break-even win % |
|---|---|---|
| Spreads / totals (−110/−110) | 4.76% | 52.38% |
| Reduced juice (−105/−105) | 2.44% | 51.22% |
| Player props (−115/−115) | 6.54% | 53.49% |
| Player props (−120/−120) | 9.09% | 54.55% |
| Parlays (2-leg, −110/leg) | ~10% | — |
| Futures | 15–50%+ | — |
The practical implication: props require a higher win rate to break even than spreads. A 53% win rate that's profitable at −110 may lose money at −120.
How to Calculate Payouts
Profit and total payout are different numbers. This is the single most common confusion on bet slips.
- Profit = what you win net above your stake
- Total payout = profit + your original stake returned
Positive odds: Profit = Stake × (Odds ÷ 100)
→ $60 at +200: $60 × 2 = $120 profit. Total payout: $180.
Negative odds: Profit = Stake × (100 ÷ |Odds|)
→ $60 at −150: $60 × 0.667 = $40 profit. Total payout: $100.
Why Odds Change Before a Game
Odds move continuously between posting and game time. Key drivers:
Sharp action: Professional bettors place large, analytically driven bets. Their money moves lines faster than mass recreational volume.
Public money: Recreational bettors systematically overbet favorites and popular players. Books shade lines to account for this — the Ohtani over is never priced neutrally.
Breaking news: A starting pitcher change, injury, or weather shift can move totals significantly within minutes. Sharp bettors react faster than books can adjust.
Reverse line movement (RLM): When the line moves against the side receiving the majority of bets. If 80% of bets are on Team A but the spread moves against them, that signals sharp backing of Team B.
The closing line — the final odds at game time — reflects all available information. Consistently getting better odds than the closing price is called Closing Line Value (CLV) and is the most reliable signal of genuine betting edge.
Line Shopping: Why the Same Bet Has Different Prices
Different sportsbooks post different odds on the same game. Getting −108 instead of −112 consistently — across hundreds of bets — adds up to meaningful real money.
- $100 bet at +120 vs +110: $10 more profit per bet
- Across 200 similar bets: $2,000 additional for identical betting decisions
- Getting −105 vs −110 on spreads: saves ~$4.55 per $100 wagered
Maintain accounts at 3+ licensed books. Check FanDuel and DraftKings for MLB props (FanDuel is widely considered the sharpest secondary market for MLB).
How to Find Value in Odds
Expected value (EV): The average profit or loss per bet if placed infinitely many times.
EV = (Win Probability × Profit) − (Loss Probability × Stake)
+EV example: Underdog at +150 (33.3% implied). You estimate 42% true probability.
EV = (0.42 × $150) − (0.58 × $100) = $63 − $58 = +$5.00
−EV example: Fair coin flip at −110 (you have no edge):
EV = (0.50 × $90.91) − (0.50 × $100) = −$4.55
That's the vig. Every zero-edge bet costs you 4.55 cents per dollar in expected value.
The key discipline: only bet when you have a genuine reason your probability estimate is higher than what the odds imply.
Common Mistakes with Odds
Confusing profit with total payout. "Potential payout" on a bet slip includes your stake returned. Profit is the net gain above that.
Thinking 50% wins = break even. It doesn't. At −110, break-even is 52.4%. Props at −120 require 54.5%.
Not shopping lines. One sportsbook means systematically missing better prices across hundreds of bets.
Overbetting heavy favorites. −300 requires 75% accuracy just to break even. One upset wipes out multiple wins.
Treating odds as sportsbook predictions. Odds are pricing tools calibrated for balanced action — not pure probability estimates.
Frequently Asked Questions
What do the + and − signs mean? Minus (−) = favorite: the number shows how much to risk to win $100 profit. Plus (+) = underdog: the number shows profit on a $100 bet.
What does −110 mean? Risk $110 to win $100 profit. The extra $10 is the vig. At −110, you need 52.38% wins to break even.
Do I have to bet exactly $100? No. $100 is a reference point. The math scales to any wager size.
Why do odds change before a game? Sharp bettor action, breaking injury news, lineup changes, and weather shifts all move lines. The closing line at game time reflects the most complete information.
Are parlays a good bet? Mathematically no — the vig compounds on every leg. Sportsbooks earn 2–4× more margin on parlays than on straight bets. They're entertainment at a steep markup, not a sustainable strategy.
Continue learning: Sports Betting Bankroll Management · The Ultimate Guide to MLB Props · The Beginner's Guide to Sports Betting
Put It to Use
See how these odds concepts apply to today's MLB slate: