Point spreads are determined in an effort to attract an equal amount of action (money wagered) on each team. For example, if the Colts are playing the Texans, odds makers will make Indy a 17-point favorite, or Colts -17, or Colts 17. This means if you bet on the Colts, they must win by more than 17 (42-3, 45-20, etc.) Then, of course, if you take Houston +17, the Texans must not lose by more than 17 (21-17, etc.). If the game ends with a 17-point margin of victory (24-7), the game is considered a push or tie. No money is lost by either party.
Most wagers also require a 10% house fee, juice or vig. To win $50 on the Colts, you would need to bet $55. Ofen, the juice will increase or decrease instead of the line moving. Again, this is all designed to maintain an equal amount of action on each side or team.
From a former bookie, the best piece of advice I can give you is to remember there’s a lot more people that know a lot more than you do whose job it is to make these point spreads. Casinos will never lose. The public is a Meatnormous Loser when it comes to betting on sports. Use that to your advantage. Don’t be afraid go against what appears to be the obvious bet. Look for lines that look strange or too good to be true. Bet on small underdogs (Redskins +2 at the Giants) and take the big favorites (Steelers -10 at Baltimore). And always bet the same amount on a very limited number of games.