How Sports Spreads Work — A Bettor's Guide

What Is a Point Spread?

A point spread is the sportsbook's estimate of the margin of victory — adjusted to make both sides of the bet roughly 50/50. If the Lakers are -6.5 against the Mavericks, the book is saying the Lakers are expected to win by about 6.5 points. To "cover" the spread, the Lakers need to win by 7 or more. To win as the Mavericks, you need them to either win outright OR lose by 6 or fewer.

Half points exist for a reason: they eliminate ties. A spread of -7 (a "flat" or "hooked" line) on an NFL favorite means if they win by exactly 7, the bet pushes — your stake refunds. -7.5 means they need to win by 8. That half point is worth more than people realize, especially on key numbers (more on this below).

Juice / Vig — Where the Book Makes Its Money

Standard spread pricing is -110 on both sides. That means to win $100, you risk $110. The extra $10 is the "juice," "vig," or "hold" — the book's built-in margin. Over thousands of bets the book wins ~52.4% of the time just by getting balanced action, because of the juice.

What this means for you: to break even at -110, you have to hit 52.38% against the spread. To beat the book you need somewhere north of 53%. The casual public hits about 49-50% — the vig grinds them out. Sharps hit 53-56% over large samples. The math is brutal but the gap is real.

Look for reduced-juice books or promotions when you can. -105 instead of -110 is a meaningful upgrade in long-term win rate.

Key Numbers in the NFL

NFL games are scored in irregular increments — 3, 6, 7 — which means some margins of victory happen WAY more often than others. The most common margins:

• 3 points — by far the most common margin (a field goal). About 14-15% of all NFL games.
• 7 points — second most common (a touchdown). About 8-9%.
• 6 points — about 6%.
• 10 points — about 6% (field goal + touchdown).
• 14 points — about 5%.

These are the "key numbers." Moving the spread on or off a key number is a much bigger deal than moving between non-key numbers. A spread that closes at -3 vs -3.5 is a roughly 2% swing in cover probability. A spread that closes at -7 vs -7.5 is about a 1-1.5% swing. A spread that closes at -4 vs -4.5 is barely 0.4%.

Practical rule: if the spread is at a key number and the line is moving toward your side, GRAB IT. Don't wait. If the line is moving away from your side and you're about to cross a key number, you've lost a meaningful chunk of value.

Key Numbers in the NBA

NBA margins are more uniform than NFL because of the higher scoring rate, but there are still mini-key numbers:

• 3, 5, 7 — common margins, but no single number dominates the way 3 does in the NFL.
• 9, 12 — slightly elevated frequency due to three-point shooting clusters.

Half-points matter less in the NBA because of the score density. -6.5 vs -7 is a much smaller swing than the same move in the NFL. But the principle still holds: when the line crosses 3 or 7, that's a more meaningful number to be on the right side of.

When To Buy Points (and When Not To)

"Buying" a half point means paying extra juice to move the spread in your favor. Standard cost is 10 cents (e.g., -110 becomes -120) for half a point off most numbers. Across the 3 in the NFL, it costs more — usually 25 cents — because the book knows it.

Rules of thumb:

• Buy through 3 in the NFL. Paying 25 cents to move from -3.5 to -3 underdog (or +2.5 to +3 favorite) is almost always +EV given how often 3 is the final margin.
• Buy through 7 in the NFL. Smaller bump, but still worth the 10-15 cents.
• Don't buy through non-key numbers. Paying 10 cents to move from -8.5 to -8 isn't worth it — the cover probability barely budges.
• Almost never buy in the NBA. The score density makes half points cheap moves with weak EV.

Alt lines (buying or selling multiple points) work the same way. The book prices them with a fat margin, but on key-number crossings they're sometimes the +EV play.

Favorites vs Dogs Against the Spread

Common myth: "dogs cover more often." The truth: dogs and favorites cover at almost exactly 50/50 over the long run, because the line is set to make it that way. What dogs do more often is COVER WITH ROOM — winning by more than expected — because variance hits them positively (an underdog winning outright covers any spread).

Where dogs DO have a small structural edge: home dogs in primetime NFL games (Sunday/Monday/Thursday night) and Sunday morning road dogs in the NFL. Both buckets have historically beaten the spread ~52-53% — small edge but real over large samples.

Where favorites have an edge: division road favorites in the NFL (familiarity offsets the typical road penalty), and elite NBA teams as small favorites against bottom-ranked opponents (the market underweights talent gaps in low-stakes regular-season games). These edges are small and don't survive after the market notices them, but they're real signals while they last.

The Line-Movement Tell

The most important number you can track on any spread is the move from open to current. If a line opens Lakers -6, closes at -7.5, and you bet -7, you got the side AT a worse price than the market settled on. The market disagreed with your read. Over time, betting against the line move is a losing strategy regardless of how individual tickets play out.

Lines move for many reasons: injuries, weather, a starter change, and where the betting volume lands. Neither the move nor the volume tells you who is right. What you can control is the price you take, so compare it with where the line opened and where it closed.

Track the opening line and closing line on every bet you make. Over a large number of bets, it is the one measure that shows whether you are consistently getting better prices than the market settles on.

Common Mistakes Casual Bettors Make

• Betting the spread on a coin-flip game. A pick-em with elevated juice is the worst bet on the board.
• Ignoring half points on key numbers. -3 and -3.5 are completely different bets. The difference matters.
• Chasing big underdogs ATS. +14 cover rate is barely above 50% — the variance is brutal and the juice is full.
• Parlaying spreads with overlapping outcomes. Lakers -7 and Lakers ML look like separate bets, but they're correlated. Most books now block these as a same-game parlay anyway.
• Betting based on TV picks or last week's talking heads. By the time a pundit calls a side on TV, the market has already moved on the info.