Betting Lines Explained: A Complete Guide to Odds, Vig & Line Shopping

Betting lines are expressed in three primary odds formats — American, decimal, and fractional. While they look different, they all communicate the same thing: how much you can win relative to your stake.

American Odds

Common in the U.S., American odds use plus (+) and minus (–) values.

• Positive odds (+200): show how much profit you’d earn from a $100 stake. Example: +200 pays $200 profit on $100 bet.
• Negative odds (–150): show how much you must stake to win $100 profit. Example: –150 requires $150 bet to win $100.

Decimal Odds

Standard in Europe, Australia, and Canada. They show the total return (stake + profit) for every $1 bet.

• Example: 2.50 odds = $2.50 return on $1 stake, which means $1.50 profit.
• Easier to compare across markets since calculations are straightforward (stake × odds = return).

Fractional Odds

Popular in the UK, especially for horse racing. They show profit relative to stake in fractional form.

• Example: 5/2 = $5 profit for every $2 staked.
• 1/4 = $1 profit for every $4 staked (heavily favored outcome).

Conversions

Most sportsbooks allow you to toggle formats. Converting odds into implied probability gives you the clearest view:

Example: Decimal 2.50 = 40% implied probability.

For beginners, mastering formats is the first step in reading betting lines. For a step-by-step walkthrough, check our full guide on how to bet.

The three most common betting lines are the moneyline, point spread, and totals (over/under). Each offers a different way to frame risk, reward, and probability.

Moneyline

A moneyline bet is the simplest line: you’re betting on which team or player wins outright.

• Example: Lakers –150 vs. Celtics +130.
  • A $150 bet on the Lakers returns $100 profit.
  • A $100 bet on the Celtics returns $130 profit.

Direct, easy to understand, but payouts vary widely based on favorites vs. underdogs. For a deeper dive, see our guide on moneyline betting.

Point Spread

The point spread levels the field between favorites and underdogs. Bettors wager on whether the favorite wins by more than the listed points or the underdog loses by fewer.

• Example: Cowboys –7.5 vs. Giants +7.5.
  • Cowboys must win by 8+ to cover.
  • Giants can win outright or lose by ≤7 and still cover.

The spread balances action and makes mismatched games more competitive for bettors.

Totals (Over/Under)

Totals focus on combined points scored by both teams, regardless of who wins.

• Example: Over/Under 210.5 in an NBA game.
  • "Over" wins if the combined score is 211+.
  • "Under" wins if the score is 210 or lower.

Totals are popular because they shift attention from team allegiance to game flow and scoring pace.

Reading a betting line means understanding the odds format, the implied probability behind it, and how much you stand to win versus your stake.

Step 1: Identify the Odds Format

Sportsbooks display odds in American, decimal, or fractional format. Knowing which system you’re looking at is the first step.

• Example: An NFL game lists the Eagles at –120 and the Cowboys at +110.

Step 2: Interpret the Line

• –120 (Eagles): You must wager $120 to profit $100.
• +110 (Cowboys): A $100 bet returns $110 profit.

This indicates the Eagles are the favorite, while the Cowboys are the underdog.

Step 3: Convert to Implied Probability

Odds show payouts, but implied probability shows the bookmaker’s assessment of the chance an event happens. Formula:

• –120: 120 / (120 + 100) = 54.5% chance.
• +110: 100 / (100 + 110) = 47.6% chance.

Step 4: Factor in Vig

If probabilities across both sides add up to more than 100%, the difference is the sportsbook’s margin, or vig. In this case: 54.5% + 47.6% = 102.1%, meaning the book built in a 2.1% edge.

Betting lines shift when sportsbooks adjust odds in response to betting volume, sharp action, or external factors such as injuries and weather. Understanding these shifts helps bettors identify and capitalize on value.

Why Lines Move

• Public Money – Recreational bettors often back favorites or popular teams. When large amounts of public money come in on one side, sportsbooks may adjust the line to balance action.
• Sharp Money – Professional bettors (known as sharps) place large wagers based on models or insider info. Books respect this action more heavily and shift lines accordingly.
• External Factors – Injuries, roster announcements, weather conditions, and even coaching news can trigger immediate adjustments.
• Market Perception – A narrative or hype cycle (e.g., a star player streaking) can push odds even without substantial betting volume.

Example Timeline

Consider an NFL game:

• Opening Line: Chiefs –3 vs. Bills.
• Midweek: Heavy sharp money arrives on the Bills, shifting line to Chiefs –2.5.
• Game Day: Weather forecast shows strong winds, lowering total from 48.5 to 45.

Each move reflects new information or risk management.

Why It Matters

Tracking line movement helps bettors identify where money is flowing and whether they should "bet early" to capture favorable odds or "bet late" to wait for overreactions.

For a deeper dive into spotting trends and timing wagers, see our full guide on betting picks, where expert analysis highlights sharp-vs-public dynamics.

The vig (also called juice) is the built-in commission a sportsbook charges on every line, ensuring profit regardless of outcome. The vig is why standard point spread odds are often listed as –110 on both sides. If you bet $110 to win $100, that extra $10 represents the bookmaker’s margin.

Example of Vig in Action

Consider an NFL spread where both teams are listed at –110:

• Bet $110 on Team A → profit $100 if they cover.
• Bet $110 on Team B → profit $100 if they cover.

Combined implied probability:

• –110 = 52.38% chance per side.
• 52.38% + 52.38% = 104.76%.

That extra 4.76% above 100% is the vig. It’s the bookmaker’s edge, guaranteeing long-term profitability even if bets are evenly split.

Why Vig Matters to Bettors

• Reduces Expected Value: Vig tilts payouts slightly against bettors.
• Varies Across Sportsbooks: Some books offer –105 lines instead of –110, which significantly reduces the house edge.
• Key in Line Shopping: Understanding vig makes it clear why comparing odds between books is critical.

Bettors who ignore vig underestimate the true cost of betting. Factoring it into every wager is essential for managing bankroll and spotting value opportunities.

Line shopping — comparing odds across multiple sportsbooks — is one of the simplest and most effective ways to maximize long-term profitability in sports betting.

Why Line Shopping Matters

Small differences in odds can have a big impact over time. For example:

• Book A lists Team X at –110.
• Book B lists the same team at –105.

A bettor wagering $100 saves $5 in risk for the same profit. Over hundreds of bets, this reduces losses and boosts expected value.

Practical Example

An NBA game total is set at 210.5 points:

• Sportsbook A: Over/Under –110.
• Sportsbook B: Over –105, Under –115.

Choosing Over –105 instead of –110 improves your long-term ROI, even though it seems like a small margin.

Tactics for Line Shopping

• Use Multiple Sportsbooks: Register with several regulated operators to compare odds before betting.
• Focus on Vig: A line at –105 instead of –110 means less vig, increasing your edge.
• Check Market Timing: Some lines are softer at open, while others become sharper closer to game time.
• Leverage Comparison Tools: Odds aggregators make it easier to find the best prices in real time.

Line shopping isn’t about chasing every tiny edge — it’s about consistently placing wagers at the most favorable price. Over time, this can be the difference between being a losing bettor and breaking even or even winning.

Beyond standard moneyline, spread, and totals, sportsbooks post props, exotic lines, and derivative markets that give bettors additional ways to find value.

Prop Bets

Props (short for proposition bets) focus on specific outcomes rather than the overall result. These can be player-based (e.g., "LeBron James Over/Under 25.5 points") or team-based (e.g., "Which team scores first?"). Props often have softer lines, making them attractive for bettors who specialize in certain matchups. For a deeper breakdown, see our full guide to prop betting.

Exotic Lines

Exotic markets include unusual or event-specific wagers that fall outside traditional categories. Examples include alternate spreads/totals, parlay combinations, or betting on unique events, such as coin tosses in the Super Bowl.

Derivative Markets

Derivative bets are tied to segments of the main game line. For instance:

• First-half totals instead of full-game totals.
• Quarter spreads in basketball.
• Team totals for specific sides.

These allow bettors to isolate edges in game flow without committing to the full outcome.

Advanced betting lines give savvy bettors more options to exploit inefficiencies. However, they require discipline, as sportsbooks often widen the vig on props and exotics compared to standard lines.

Most bettors lose money on betting lines because they misunderstand odds, ignore movement, or fail to shop for value. Avoiding these mistakes is essential for long-term improvement.

• Misreading Odds Formats. Confusing American, decimal, or fractional odds leads to poor stake calculations and unrealistic expectations.
• Ignoring Line Movement. Betting too early or too late without monitoring shifts can result in taking a worse price than what was available.
• Neglecting Vig. Failing to account for juice means underestimating the true cost of a bet and overvaluing potential returns.
• Betting Into Inflated Lines. Popular teams often attract substantial public funding, which can inflate odds. Chasing them after movement reduces your edge.
• Skipping Line Shopping. Settling for one sportsbook’s price instead of comparing multiple books leaves long-term value on the table.

Betting lines are the backbone of sports wagering. They determine payouts, reflect market sentiment, and reveal the sportsbook’s edge through vig. Mastering how lines work is essential for anyone serious about betting.

By learning how to read odds, track line movement, factor in vig, and shop for the best prices, bettors can transform raw numbers into actionable insights. Advanced markets like props and derivatives expand the opportunities but require even greater discipline.

To continue building your knowledge beyond betting lines, explore BettingRanker’s complete library of betting guides, where you’ll find strategies and resources designed to help you bet smarter and with confidence.