Definition
Line shopping means checking multiple sportsbooks before placing a bet so you can take the best available price or point spread. The “line” is the number attached to a wager, such as Chiefs -3, Over 47.5, or Yankees -120.
For American odds, implied probability is:
Negative odds: odds / (odds + 100) using the absolute value
Positive odds: 100 / (odds + 100)
Better odds lower the break-even rate needed for the same bet.
Worked Example
You want to bet Team A to win.
Book 1 offers Team A at -110.
Book 2 offers Team A at -105.
Book 3 offers Team A at +100.
A $110 bet at -110 wins $100.
A $105 bet at -105 wins $100.
A $100 bet at +100 wins $100.
The implied probability at -110 is 110 / (110 + 100) = 52.38%.
The implied probability at +100 is 100 / (100 + 100) = 50.00%.
If your projection says Team A wins 52% of the time, -110 is below break-even, while +100 is above break-even.
Why It Matters
Line shopping helps a bettor turn the same opinion into a better expected value by reducing the price paid. It matters most in high-volume betting, tight markets, point spreads near key numbers, and props where prices vary across books.