Compare Lines Calculator

How to Compare Different Spread Lines

When you see -3 at -115 at one sportsbook and -3.5 at +100 at another, which line is actually better value? You can't just compare the juice — you need to account for the probability value of the spread difference.

The Math Behind Line Comparison

This calculator uses historical margin of victory frequency data for each sport. In the NFL, for example, 15.5% of games are decided by exactly 3 points, and 9.5% by exactly 7 points. A half-point through these key numbers is worth significantly more than through non-key numbers.

NFL Key Numbers

• 3: 15.5% of games decided by exactly 3 — a half-point through 3 is worth ~7.75%
• 7: 9.5% of games — half-point worth ~4.75%
• 10: 5.8% of games — half-point worth ~2.9%
• 14: 5.3% of games — half-point worth ~2.65%

Example: -3 (-115) vs -3.5 (+100)

Line A: -3 at -115 = 53.5% implied probability
Line B: -3.5 at +100 = 50.0% implied probability
Half-point value through 3 in NFL: 7.75%
Line A is better by approximately 7.75% - 3.5% = 4.25%